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Doctoral Degrees (Plant Breeding)

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    Breeding bambara groundnut (vigna subterranea (L.) verdc) for enhanced yield and nutritional quality in South Africa.
    (2023) Majola, Nomathemba Gloria.; Shimelis, Hussein.; Gerrano, Abe Shegro.
    Bambara groundnut (Vigna subterranea (L.) Verdc.; 2n= 2x = 22) is a nutrient-dense grain legume cultivated in sub-Saharan Africa (SSA) and Asia. The current food systems in tropical and subtropical regions depend on the cultivation and use of a few commodity crop species. This causes most indigenous crop species, such as Bambara groundnut, to remain neglected by researchers and underutilised in the value chains. Underutilised crop species have received limited research and development attention from researchers and policymakers, and hence, their economic value, production methods, seed enterprises, product development and commercialisation are not yet fully explored. Due to a lack of systematic genetic improvement, the yield of most underutilised crops is low (<0.85 ton ha-1) and stagnant. Unlocking Bambara groundnut’s economic and value-adding potential as an essential multipurpose food and cash crop will enhance food and nutritional security in developing countries. Research on Bambara groundnut in South Africa is relatively peripheral and there are no known improved varieties of this crop with high yield and nutritional quality. Therefore, specific objectives of this study were: (1) to document the progress made on Bambara groundnut production, utilisation and genetic improvement in SSA to discern the key production constraints, genetic resources and analysis, breeding methods and gains on yield and nutrition to guide breeding; (2) to assess them genotype-by-environment interaction (GEI) effect on grain yield and to select best adapted Bambara groundnut genotypes in South African target production areas for breeding; (3) to determine the compositions of phytochemicals and mineral elements present in Bambara groundnut genetic pool to identify superior and contrasting genotypes to guide product development and breeding; (4) to determine the magnitude of the genetic diversity and population structure of Bambara groundnut collections of South Africa using high throughput single nucleotide polymorphisms (SNP) markers to complement phenotypic and nutrition profile data for genotype selection and breeding; and (5) to determine the combining ability effects and gene action conditioning yield and related traits in Bambara groundnut genotypes to identify the best combiner donor parents and progenies for genetic advancement, cultivar development and release. The first part of the study reviewed progress on Bambara groundnut production, utilisation and genetic improvement in SSA. The study presented key production constraints, genetic resources and analysis, breeding methods and genetic gains on yield and nutritional quality. Modern crop management, production technologies, and value chains are yet to be developed in Africa to achieve economic gains from Bambara groundnut production and marketing. Improved crop management and post-harvest handling technologies, modern varieties with high yield and nutritional quality, value addition and market access are among the key considerations in current and future Bambara groundnut research and development programs. Information presented will guide sustainable production and effective crop breeding to pursue food and nutrition security and improved livelihoods through Bambara groundnut enterprises. In the second chapter of the study, 75 Bambara groundnut genotypes were evaluated across seven selected environments using a 5 x 15 alpha lattice design with three replications. The study revealed significant (p<0.05) differences among genotypes (G), environments (E) and GEI effects on grain yield. A high proportion of the observed variation was due to GEI (36.62%), followed by environment (35.63%) and genotype (24.16%) effects. Grain yield across environments ranged from 1.4 ton ha-1 for ARC Bamb-68 to 0.10 ton ha-1 for ARC Bamb-74. Genotype ARC Bamb-68 (0.96 ton ha-1), ARC Bamb-9 (0.88 ton ha-1) and ARC Bamb-54 (0.84 ton ha-1) attained the highest grain yield across locations, while ARC Bamb-74 exhibited the lowest grain yield of 0.16 ton ha-1. The genotype and genotype-by-environment biplot identified ARC Bamb-17, ARC Bamb-14, ARC Bamb-20, ARC Bamb-18, ARC Bamb-14, and ARC Bamb-26 as the most stable genotypes across locations, while ARC Bamb-18 and ARC Bamb-54 were specifically adapted to Loskop and Brits. The Mafikeng site was ideal for Bambara groundnut evaluation, genotype differentiation, and large-scale seed production. The selected genotypes with high grain yields and stability are valuable genetic resources as breeding parents for Bambara groundnut improvement in South Africa. In the third chapter of the study, 75 genetically diverse Bambara groundnut genotypes were field evaluated across four environments using a 15 x 5 alpha lattice design with three replications during the 2020-2021 cropping season. Genotypes were profiled for fat, phenolic and flavonoids contents at the Agricultural Research Council (ARC) analytical laboratory in South Africa. Further, the genotypes were assessed for the contents of the following minerals: calcium (Ca), iron (Fe), potassium (K), phosphorus (P), zinc (Zn) and nitrogen (N). The nutritional content of the test genotypes varied significantly (P<0.05), which were affected by the genotype and environment interactions. The Ca, Fe, K and Zn content varied from 150.70 to 216.53, 4.30 to 16.77, 771.99 to 1155.89 and 5.50 to 7.17 mg.100 g−1 dry seed sample, respectively. Genotypes, including ARC Bamb-2, ARC Bamb-19, ARC Bamb-73, ARC Bamb-56, ARC Bamb-37, ARC Bamb-3 and ARC Bamb-69 exhibited the highest fat content (>6.00 %). ARC Bamb-40 and ARC Bamb-59 recorded a higher mean Fe content of 16.00 mg.100 g−1. ARC Bamb-2 was the top-performing genotype with high fat content (6%), Ca (211.93 mg.100 g−1), and Zn (7.17 mg.100 g−1 ). Ca, K, and N contents displayed strong correlations (r>0.60, P<0.05). Phosphorus and Zn contents exhibited moderate correlations with Ca. Overall, the study selected genotypes ARC Bamb-73, ARC Bamb-19, ARC Bamb-9 and ARC Bamb-2 with high compositions of essential nutrients for product development or breeding. The selected genetic resources are valuable for trait integration and developing new breeding populations with enhanced nutrient compositions and agronomic and market-preferred traits. In the fourth part of the study, the magnitude of the genetic diversity and population structure of South Africa Bambara groundnut collections was determined using high throughput single nucleotide polymorphisms (SNP) markers. Ninety-three genotypes were genotyped with 2286 SNP markers and phenotyped with some unique complementary morpho-agronomic traits of the crop. The mean genetic diversity value was 0.32, revealing moderate genetic differences among the assessed genotypes. Cluster and structure analyses grouped the tested genotypes into two distinct categories. Further, the analysis of molecular variance partitioned the total genetic variation into among genotypes (90%), within genotypes (8%) and among populations (2%). The results revealed two heterotic groups for hybridisation and selection programs. The following unique genotypes were selected: ARC Bamb-37 (with spreading growth type), ARC Bamb-49 (bunch type), ARC Bamb-61 (semi-bunch) and ARC Bamb-83 (spreading) using the SNP markers and desirable agronomic traits. The study provided new insight on Bambara groundnut genetic profiles of South African collections, which will assist in conservation strategy and management of the crop for effective breeding. The final part of the study assessed combining ability effects and gene action conditioning yield and related traits in Bambara groundnut genotypes to identify the best combiner donor parents and progenies for genetic advancement and breeding. Ten contrasting parents were selected and crossedusing a 10 × 10 half-diallel mating design, and 45 progenies developed. The progenies and their parents were field evaluated using a 5 × 11 alpha lattice design with two replications in two contrasting locations in South Africa. Data was collected on agronomic traits and subjected to statistical analyses to compute genetic parameters. Genotype × location interaction effect was significant (P < 0.05) for the studied agronomic traits. General combining ability (GCA) and specific combining ability (SCA) effects were significant in most assessed agronomic traits, including yield per plant. The GCA × location and SCA × location interaction effects were significant for most traits. A Baker’s ratio of < 1 were recorded for most assessed traits, indicating the preponderance of non-additive gene effects conditioning the traits. The parental lines such as ARC Bamb-25, ARC Bamb-8 and ARC Bamb-55 recorded positive and desirable GCA effects for yield per plant. The progenies ARC25×ARC8, ARC44×ARC9 and ARC6×ARC9 had desirable SCA effects for yield per plant, ARC44×ARC8, ARC44×ARC68, ARC42×ARC8 for higher number of secondary branches per stem, ARC25 ×ARC8 for early maturity, ARC42×ARC55 for higher number of pods per plant and ARC42 ×ARC57 for increased seed width. The new families selected in the current study are useful breeding populations and will be subjected to selection and multilocation evaluation to release the best-performing varieties. Overall, the present study appraised the present production constraints, genetic resources and analysis, breeding methods and genetic gains on yield and nutritional quality to guide future breeding. Moreover, new Bambara groundnut breeding populations were developed with enhanced yield and nutritional compositions for genetic advancement and multilocation selection for variety release and adoption in South Africa.
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    Genetic characterization of citron watermelon (citrullus lanatus var. citroides [L.H. Bailey] mansf. ex greb.) and development of experimental hybrids.
    (2023) Ngwepe, Mantlo Richard.; Shimelis, Hussein.; Mashilo, Jacob.
    Citron watermelon (Citrullus lanatus var. citroides [L.H. Bailey] Mansf. ex Greb.) is indigenous to sub-Saharan Africa (SSA) with multiple uses, including human food and animal feed. Its succulent leaves are used as leafy vegetables, while the ripened yellow and orange-fleshed fruits are used to prepare various traditional dishes, and the seeds are roasted and consumed as snack. It is an emerging potential rootstock for producing grafted sweet watermelon (Citrulus lanatus var. lanatus) to improve fruit yield and biotic and abiotic stress tolerance. It is also a source of novel genes for breeding in sweet watermelon to improve fruit yield, quality and disease resistance. Citron watermelon in SSA is mainly cultivated using unimproved landrace varieties. Landraces exhibit marked phenotypic variation for fruit shape, size, skin colour patterns, and seed coat colours. Phenotypic and genetic variation among South African citron watermelon landraces is yet to be systematically assessed for diverse use and cultivar design. The overall goal of this study was to initiate a pre-breeding program for citron watermelon through identification and selection of unique and complementary genotypes for production, value-adding and breeding. The specific objectives of this study were: i. To determine the extent of genetic diversity among South African citron watermelon landrace accessions using selected simple sequence repeat (SSR) markers to identify genetically divergent accessions for trait integration and variety development; ii. To assess the phenotypic diversity of citron watermelon landrace accessions of South Africa and to select desirable genotypes with suitable agronomic and horticultural traits for direct production, breeding and conservation; iii. To estimate variance components, heritability and genetic advance of phenotypic traits in citron watermelon to guide the selection of superior genotypes for direct production and breeding; iv. To determine the combining ability and hybrid performance of citron watermelon genotypes for agronomic traits for breeding. In the first study, 48 citron watermelon landrace collections widely grown in the Limpopo Province of South Africa were genotyped using 11 selected SSR markers. The SSR markers amplified a total of 24 alleles, with a mean expected heterozygosity value of 0.38, indicating moderate genetic diversity among the studied accessions. Analysis of molecular variance attributed 8%, 75%, and 17% of the molecular variation between populations, among accessions and within accessions, respectively. Three distinctive genetic groups were identified based on cluster analysis. The following distantly related genotypes are recommended as breeding parents namely: WWM03, WWM04, WWM15, WWM16, WWM18, WWM22, WWM23, WWM24, WWM25, WWM26, WWM28, WWM33, WWM34, WWM35, WWM38, WWM39, WWM41, WWM66, WWM76, WWM78, WWM81, WWM84, WWM86 and WWM89 (selections from Cluster I), WWM14, WWM37, WWM42, WWM44, WWM46, WWM50, WWM65, WWM79, WWM85 and WWM87 (Cluster II), and WWM38, WWM47 and WWM48 (Cluster III). These are useful parental lines for pre-breeding to develop and release new varieties with multiple uses. In the second study, 36 selected citron watermelon landrace accessions were evaluated under field conditions across two environments using a 6 × 6 lattice design with three replicates. Data on key qualitative and quantitative traits were collected and subjected to non-parametric and parametric statistical analyses. The accessions showed wide phenotypic variation and unique traits for genetic improvement. Positive and significant correlations (p < 0.001) were recorded between total fruit yield per plant with plant height (r = 0.64), number of harvestable fruits (r = 0.70), number of marketable fruits (r = 0.73) and marketable fruit yield (r = 0.96). Seed yield per plant positively and significantly (p < 0.001) correlated with number of male flowers (r =0.68), plant height (r = 0.61) and total fruit yield (r = 0.79). Principal component analysis identified nine components which accounted for 86.38% of total variation amongst accessions for assessed phenotypic traits. The study recommended citron watermelon accessions such as WWM14, WWM16, WWM39, WWM41, WWM67 and WWM79 for use as leafy vegetables owing to their profuse branching ability and longer vine production. Whereas accessions including WWM03, WWM17, WWM35, WWM40, WWM50, WWM67, WWM79 and WWM85 are selected with larger fruit size. Accessions WWM05 and WWM09 are sour-flesh types which are suitable genetic stocks for breeding sweet-and-sour and sweet dessert watermelons. Orange-fleshed accessions such as WWM03, WWM04, WWM46, WWM64, WWM66 and WWM67 are recommended for fresh consumption, cooking, processing or variety design. Accessions WWM02, WWM03, WWM08, WWM14, WWM16, WWM23, WWM38, WWM40, WWM41 and WWM67 have red and white seed coat colour which are superior selections to prepare roasted citron watermelon seed snack. In the third study, variance components, heritability and genetic gains of phenotypic traits were estimated involving 36 accessions of citron watermelon grown under field conditions across two test environments using a 6 × 6 lattice design with three replicates. High broad-sense heritability and genetic advance as percent of the mean were recorded for fruit length at 83.86 and 4730.45%, seed length (77.73 and 1731.27%), hundred seed weight (73.73 and 4027.36%), fruit diameter (70.44 and 2949.64%) and fruit weight (70.39 and 8490.05%), respectively. Step-wise regression analysis revealed marketable fruit yield and total number of fruits per plant explaining 89% (R2 = 0.89) of total variation for total fruit yield per plant, whereas number of seed per fruit and hundred seed weight explained 92 (R2 = 0.92) of total variation for seed yield per fruit. Citron watermelon landrace accessions WWM03, WWM14, WWM16, WWM39, WWM65, WWM67 and WWM79 with high total fruit yield and seed yield per fruit were selected for production or breeding programme. In the fourth study, five selected parental genotypes were crossed in a 5 × 5 half-diallel mating design to develop 10 hybrids. The 15 families (five parents and 10 F1 hybrids) were evaluated across two environments using a randomized complete block design (RCBD) with three replications. General combining ability (GCA) and specific combining ability (SCA) effects were significant (p < 0.001) for most traits. Environment × GCA was non-significant, whereas Environment × SCA effects were significant (p < 0.001) for most traits. The ratios of GCA/SCA variances were less than unity for most traits, indicating non-additive gene action of the traits. Broad-sense heritability varied from low to moderate, implying variable selection response of the assessed traits among the F1 hybrids. The parental genotypes WWM16 with positive GCA effects for fruit and seed yield and WWM66, with positive GCA effects for the number of seeds per fruit and seed yield, were identified for hybrid breeding. The following F1 hybrids, namely: WWM04 × WWM16, WWM03 × WWM66 and WWM16 × WWM50 with positive SCA effects on total fruit yield per plant and marketable fruit yield per plant, and WWM04 × WWM50, WWM03 × WWM16 and WWM03 × WWM66 with positive SCA effects for number of seeds per fruit and total seed yield were identified. The study identified novel and best-performing F1 hybrids of citron watermelon for economic traits and are recommended for multi-environmental evaluations, variety registration and commercialization. Overall, the study revealed genetic and phenotypic variation in citron watermelon to select and recommend suitable genotypes for production and for breeding new generation varieties based on market needs and consumer preferences. The study recommends accessions such as WWM14, WWM16, WWM39, WWM64, WWM67, WWM76 and WWM79 with high fruit yield, and WWM03, WWM04, WWM14, WWM15, WWM16, WWM24, WWM28, WWM37, WWM46, WWM66 and WWM68 exhibiting high fruit and seed yield for breeding or direct production. The parents WWM04, WWM03 and WWM16 were identified as good combiners for fruit or seed yield and related-component traits for future breeding. The F1 hybrids derived from these parents, including WWM04 × WWM16, WWM03 × WWM16, WWM03 × WWM66, WWM16 × WWM50, and WWM04 × WWM50 were best performing for economic traits and new breeding population development.
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    Pre-breeding of okra (abelmoschus esculentus [L.] moench) for drought tolerance.
    (2023) Mkhabela, Sonto Silindile.; Shimelis, Hussein.; Gerrano, Abe Shengro.
    Okra (Abelmoschus esculentus [L.] Moench; 2n = 2x = 130) is an important vegetable and oil crop. It is extensively grown in tropical and subtropical regions with limited and erratic rainfall conditions. A lack of improved cultivars with drought tolerance hinders the production of okra in sub-Saharan Africa (SSA). Considerable phenotypic and genotypic variation present in okra genetic resources from SSA useful for cultivar design with enhanced fresh pod and oil yields and drought tolerance. However, the genetic diversity in SSA’s okra germplasm collection is yet to be explored for breeding targeting economic and horticultural traits. There has been limited progress in the breeding of okra for drought tolerance. Therefore, the specific objectives of this study were i) to determine the response of selected okra genotypes to drought stress using fresh fruit yield and yield-related traits to identify and select candidate genotypes for drought tolerance breeding, ii) to determine genetic diversity present among okra accessions using simple sequence repeats (SSR) and complementary phenotypic markers and to select genetically divergent and superior parental accessions for pre-breeding, iii) to assess the levels of drought tolerance in preliminarily selected okra accessions based on leaf gas exchange and chlorophyll fluorescence to determine best-performing genotypes for drought-tolerance breeding and iv) to determine the combining ability and heterosis of selected okra accessions for yield and yield-related traits to identify superior parents and progenies for breeding. The first part of the study involved 26 okra genotypes that were evaluated in glasshouse and field environments under drought-stressed (DS) and non-stressed (NS) conditions using a 13 × 2 alpha lattice design with two replications. The findings revealed significant (P < 0.05) genotype x testing environment x water condition interaction effects for most traits, allowing for the selection of okra genotypes suited for drier conditions. Yield per plant (YPP) positively and significantly correlated with fresh pod length (FPL) (r = 0.66; P ≤ 0.001), dry pod weight (DPW) (r = 0.80; P ≤ 0.001) and number of pods per plant (NPP) (r = 0.58; P ≤ 0.001) under DS condition in the field environment. The study identified genotypes with high yield and other desirable phenotypic attributes, which are useful genetic resources for future crosses and the selection of promising progenies based on combining abilities analyses and heritability under water-limited environments. In the second study, 26 preliminarily selected okra accessions were assessed using nine highly polymorphic SSR markers and phenotyped under DS and NS environmental conditions using a 13 × 2 alpha lattice design with two replications. The SSR markers revealed a mean heterozygosity value of 0.54, indicating moderate genetic diversity among the tested okra accessions. Cluster analysis based on phenotypic and SSR markers differentiated the accessions into three distinct genetic groups. Pod yield per plant (PYPP) was positively and significantly correlated with fresh pod length (FPL) (r = 0.81), above-ground biomass (ABG) (r = 0.69), and harvest index (HI) (r = 0.67) under DS conditions, and FPL (r = 0.83) and AGB (r = 0.60) under NS conditions. Genetically complementary accessions such as LS04, LS05, LS06, LS07, LS08, LS10, LS11, LS15, LS18, LS23, LS24, and LS26 were identified for their high yield potential and related yield-improving traits under DS conditions. The identified accessions were recommended as parents for hybridization and selection programs to improve the yield potential of okra under drought-stressed environments. In the third part of the study, 26 genetically diverse okra accessions were screened for physiological traits response under NS and DS conditions in a controlled glasshouse environment using a 13 × 2 alpha lattice design and three replications in two growing seasons. Statistical analyses revealed a significant genotype × water condition interaction effect for transpiration rate (T), net CO2 assimilation (A), intrinsic water use efficiency (WUEi), instantaneous water use efficiency (WUEins), minimum fluorescence (Fo′), maximum fluorescence (Fm′), maximum quantum efficiency of photosystem II photochemistry (Fv′/Fm′), the effective quantum efficiency of PSII photochemistry (ɸPSII), photochemical quenching (qP), nonphotochemical quenching (qN) and relative measure of electron transport to oxygen molecules (ETR/A). The results suggested variable drought tolerance of the studied okra accessions for selection. Seven principal components (PCs) contributing to 82% of the total variation for assessed physiological traits were identified under DS conditions. Leaf gas exchange parameters, T, A and WUEi, and chlorophyll fluorescence parameters such as the ɸPSII, Fv′/Fm′, qP, qN, ETR and ETR/A had high loading scores and correlated with WUEi, the ɸPSII, qP and ETR under DS conditions. The study identified drought-tolerant accessions, namely LS05, LS06, LS07 and LS08 based on high A, T, Fm′, Fv′/Fm′ and ETR, and LS10, LS11, LS18 and LS23 based on high AES, Ci, Ci/Ca, WUEi, WUEins, ɸPSII and AES. The selected genotypes are high yielding (≥5 g pods/plant) under drought stress conditions. The data presented will complement phenotypic data and guide breeding for water-limited agroecologies. Eight selected okra genotypes were crossed in the fourth part of the study to generate new genetic combinations and breeding populations. The parents were selected based on their high yield potential and tolerance to drought stress. The genotypes were sourced from the Agricultural Research Council-Vegetable, Industrial and Medicinal Plants (ARC-VIMP), South Africa, assembled from diverse regions of origin. The selected eight parents were crossed using an 8 × 8 half diallel mating design during the 2021 cropping season. The parents were planted under field conditions at the ARC-VIMP research station during the 2021/2022 growing season. Subsequently, 28 new generations were developed. The crosses and eight parents were field evaluated using a 12 × 3 lattice design with three replications. The genotypes were evaluated under NS and DS conditions at two locations, namely the ARC – Loskop and ARC – Brits sites. Significant (P<0.01) effects of genotype, environment, and genotype × environment interaction was recorded for fresh pod yield and component traits. General combining ability (GCA) and specific combining ability (SCA) effects were significant (P<0.05) for most traits, indicating the role of additive and non-additive gene action underlying the inheritance of the assessed traits. The GCA × environment and SCA × environment interaction effects were significant for days to flowering (DTF), number of leaves per plant (NOL), fresh pod length (FPL), number of fresh pods per plant (NFPP) and pod yield per plant (PYP). Parental genotypes LS09, LS10 and L24 showed positive GCA effects for PYP under DS conditions and were selected to be valuable germplasm for variety design to widen genetic variability for drought tolerance and yield-related traits. Crosses LS01 × LS17, LS01 × LS18, LS09 × LS10, LS09 × LS18, LS09 × LS24, LS15 × LS18, LS15 × LS21, LS15 × LS24 and LS17 × LS21 expressed positive SCA effects for PYP under DS condition and are recommended for genetic advancement, production, and commercialization in water-scarce environments of South Africa. Overall, the study discerned considerable genetic diversity among the evaluated okra genotypes. Further, the study selected parental lines and new families with good product profiles, drought tolerance and combining ability for genetic advancement and variety design for water-limited environments in South Africa and similar agroecologies.
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    Genetic analysis for drought tolerance and biomass allocation in newly developed populations of bread wheat (triticum aestivum L.).
    (2023) Shamuyarira, Kwame Wilson.; Shimelis, Hussein Ali.; Chaplot, Vincent A. M.; Figlan, Sandiswa.
    Bread wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD) is the most lucrative commodity crop cultivated worldwide. Wheat productivity is crucial for economic gains and food security to the growing global population. Global wheat production is affected by recurrent droughts that are further exacerbated by a changing climate characterized by rising temperatures and erratic rainfall. In response to these challenges, most wheat breeding programs have focused on increasing harvest index to improve grain yield and drought adaptation without considering below-ground root biomass. In recent years there has been a growing interest in using crops such as wheat to store some of the atmospheric carbon previously lost from soils due to past agricultural practices to sustain soil quality and to mitigate climate change. Increasing biomass allocation of new wheat genotypes to the root system may enhance carbon (C) extraction from the atmosphere and transfer to crop tissues and to soils through carbon sequestration while increasing resilience to drought stress by improving water and nutrient uptake. Therefore, this study aimed at improving drought tolerance and C sequestration ability of wheat for production under dryland farming systems. The specific objectives were: to provide information based on a retrospective quantitative genetic analysis on combining ability studies of wheat for yield and yield-related traits to predict potential genetic gains achievable in improving biomass allocation for drought tolerance and soil carbon storage; to determine the extent of genetic variation present in wheat germplasm collections for biomass allocation and drought tolerance based on complementary phenotypic and root attributes and high-density single nucleotide polymorphism (SNP) markers to select breeding parents; to estimate the magnitude of the relationships between root biomass and yield components and to identify influential traits to optimise genotype selection for enhanced biomass allocation, drought tolerance and carbon sequestration potential in bread wheat (Triticum aestivum L.); to determine the general and specific combining ability, maternal effects and the mode of gene action controlling the major yield-related traits and biomass allocation in wheat to identify good combiners for breeding and enhanced carbon sequestration, and; to determine the genetic variability of newly developed wheat populations for grain yield and biomass allocation under different water stress conditions to select the best-performing families for advancement. The first study compared data on the general combining ability (GCA) and specific combining ability (SCA) effects of wheat for yield and related traits under optimum and drought-stressed conditions from 40 studies worldwide. Days to heading (DTH), plant height (PH), number of tillers per plant (TN), kernels per spike (KPS), 1,000-kernel weight (TKW), shoot biomass (SB), and grain yield (GY) exhibited wide variation for GCA and SCA effects. Progeny performance increased by 14.30 and 4.04% for SB and GY, respectively, compared with parental values under optimum water conditions. The number of tillers and SB exhibited positive associations with GY (0.45 ≤ r ≤ 0.85, p < 0.05) under both water conditions. Meta effect sizes for drought stress were negative. The highest meta-effect sizes were calculated for DTH (−4.5) followed by SB (−2.0), whereas KPS (−1.25) had the lowest. The genetic gains for PH, SB, and other yield components showed that divergent crosses involving complementary parents could enhance biomass allocation patterns in wheat. This could be used as a basis for improving biomass allocation to roots. In the second study, a total of 97 bread wheat genotypes were evaluated in field and greenhouse trials under drought-stressed and non-stressed conditions and genotyped using 16 382 high-density single nucleotide polymorphism (SNP) markers. The analysis of molecular variance showed that the intrapopulation variance was very high at 99%, with a small minimal inter-population variance (1%). The genetic distance, polymorphic information content and expected heterozygosity varied from 0.20 to 0.88, 0.24 to 1.00 and 0.29 to 0.58, respectively. The cluster analysis based on SNP data showed that 44% and 28% of the assessed genotypes maintained their genetic groups compared to hierarchical clusters under drought-stressed and non-stressed phenotypic data, respectively. The joint analysis using genotypic and phenotypic data resolved three heterotic groups and allowed the selection of genotypes BW140, BW152, BW157, BW162, LM30, LM47, LM48, LM52, LM54 and LM70. The selected genotypes were the most genetically divergent, with high root biomass and grain yield and are recommended for production or breeding. The third study evaluated 100 wheat genotypes consisting of 10 parents and 90 derived F2 families under drought-stressed and non-stressed conditions at two different sites. Data were collected for DTH, days to maturity (DTM), PH, TN, spike length (SL), spikelets per spike (SPS), KPS, TKW, SB, root biomass (RB), total plant biomass (PB), root-to-shoot ratio (RS) and GY. There was significant (p < 0.05) genetic variation in most assessed traits except TN and RS. Root biomass had significant positive correlations with grain yield under drought-stressed (r = 0.28) and nonstressed (r = 0.41) conditions, but a non-significant correlation was recorded for RS and grain yield. Notably, both root and shoot biomass had significant positive correlations under both water regimes, revealing the potential to increase both traits with minimal biomass trade-offs. The highest positive direct effects on grain yield were found for KPS and PB under both water regimes. The present study demonstrated that selection based on KPS and PB rather than RS will be more effective in ideotype selection of segregating populations for drought tolerance and carbon sequestration potential. In the fourth study, the above dataset from the ten parental lines and their F2 progeny were subjected to combining ability analysis using a full-diallel mating design. Significant differences were recorded among the tested families revealing substantial variation for PH, KPS, RB, SB, PB and GY. Additive gene effects conditioned PH, SB, PB and GY under drought, suggesting the polygenic inheritance for drought tolerance. Strong maternal and reciprocal genetic effects were recorded for RB across the testing sites under drought-stressed conditions. The parental line LM75 maintained the GCA effects in a positive and desirable direction for SB, PB and GY. Early generation selection using PH, SB, PB and GY will improve drought tolerance by exploiting additive gene action under drought conditions. Higher RB production may be maintained by a positive selection of male and female parents to capture the significant maternal and reciprocal effects found in this study. The fifth study showed higher phenotypic coefficient of variation (PCV) than the genotypic coefficient of variation (GCV) for PH, KPS, SB, RB, PB and GY. Moderate heritability of 41.61% and 45.14% and genetic advance as a percentage of the mean (GAM) of 3.49% and 3.58% were observed for RB under drought and for KPS under non-stressed conditions, respectively. Based on correlation and principal component analysis, geometric mean productivity (GMP) and stress tolerance index (STI) were identified as the most efficient drought tolerance indices for selecting drought-tolerant families with high RB. Direct crosses such as BW162 × LM75, BW152 × LM75, LM70 × LM75, LM71 × LM75 and LM26 × LM75 and reciprocal crosses LM48 × BW140, LM71 × LM26, LM70 × BW152, LM70 × BW141 and LM75 × LMBW152 were identified as drought tolerant and are recommended for genetic advancement. The high root biomass production of these families will contribute to carbon inputs through rhizodeposition in agricultural soils. Further research studies should investigate the link between changes in biomass allocation and atmospheric carbon transfer to soils for improving soil quality and mitigating climate change. The present study revealed that maternal and reciprocal effects should be considered when selecting root biomass and biomass allocation traits. Also, the study identified drought tolerant genotypes and developed new families with high biomass production for enhanced carbon sequestration. The identified families should be advanced for variety development and further evaluated for their net carbon contribution to the soil.
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    Pre-breeding of sorghum [sorghum bicolor (L.) moench] for drought tolerance in the semi-arid zones of Nigeria=Ukulungisela ukuzalanisa kweSorghum [Sorghum bicolor (L.) Moench] Yokubekezelela Isomiso Ezindaweni Ezomile ZaseNigeria.
    (2023) Yahaya, Muhammad Ahmad.; Shimelis, Hussein Ali.
    Sorghum [Sorghum bicolor (L.) Moench] is a staple food crop serving millions of people in Africa and Asia's arid and semi-arid agro-ecologies. Sorghum is widely cultivated in Northern Nigeria, serving diverse value chains, including the food and feed sectors and the brewery industry. However, the potential production and productivity of sorghum in Africa, including Northern Nigeria, is constrained by severe drought stress associated with climate change. Furthermore, smallholder farmers in Nigeria still cultivate low-yielding and drought-susceptible unimproved sorghum landraces. Developing drought-tolerant sorghum cultivars adapted to semi-arid regions would enhance yield gains and stability with desirable product profiles according to the needs of the farmers and the marketplace. Therefore, the overall objective of this study was to improve sorghum productivity in Nigeria by developing new generation, locally adapted and drought-tolerant varieties. The specific objectives of this study were to: (1) present the current opportunities and constraints to sorghum production in Nigeria and make recommendations as a guide to new variety design and sustainable production, (2) determine drought tolerance and genotype-byenvironment interaction (GEI) effect on grain yield of a population of African sorghum genotypes to identify high-yielding and drought-adapted genotypes for production and breeding, (3) assess the genetic diversity and deduce the population structure among 200 sorghum accessions to guide the selection of contrasting parents for pre-breeding and breeding of drought-tolerant sorghum cultivars and (4) determine the combining ability, heterosis and gene action conditioning agronomic traits and grain yield among sorghum genotypes to select genetically superior and contrasting parental genotypes and new families for drought tolerance breeding, cultivar release and commercialization. In the first chapter, a participatory rural appraisal (PRA) study was conducted in three selected sorghum growing zones in Northern Nigeria involving 250 farmers. Socio-economic data were collected through surveys and focus group discussions. Results showed that sorghum was cultivated mainly by males (80%) who had grade 6-12 level of education (31.3%), with a productive age of 21-45 years (75.7%) and a household family size of below five members (52.3%). Low-yielding landrace varieties such as Kaura (37.4%) and Fara-fara (29.3%) were the most widely cultivated types across the study zones due to their good grain quality. The major farmers' preferred traits from a sorghum variety were high yield, drought tolerance and Striga resistance. The study recommends integrated sorghum technology development incorporating the described preferences of the farmers for sustainable production and economic gains of the crop. The second chapter examined 225 sorghum genotypes assembled from diverse origins to determine drought tolerance and GEI effects on grain yield. The collections were evaluated under non-stressed (NS), pre-anthesis drought stress (PreADS), and post-anthesis drought stress (PoADS) conditions under field and greenhouse environments. The additive main effect and multiplicative interaction (AMMI) analysis revealed that genotype (G), environment (E), and GEI were significant (p<0.05) and accounted for 38.7, 44.6, and 16.6% of the total explained variation in grain yield, in that order. AMMI 4 was the best-fitting model for genotype selection with better grain yield. Based on AMMI 4 and the Best Linear Unbiased Predictors (BLUPs) analyses, genotypes Yar Lazau and Dangama Wulchichi, with a grain yield of 5.6 t/ha and 6.3 t/ha, were selected as being suitable for non-stressed conditions, respectively. Genotypes ICNSL2014-022-4 and Takumbo with BLUPs of 2.5 t/ha and 2.6 t/ha were best-suited for pre-anthesis drought stress conditions, whereas genotypes Danyar Bana and Gagarau - 4 with BLUPs of 4.2 t/ha and 4.3 t/ha are recommended for post-anthesis drought-prone environments, respectively. The identified sorghum genotypes are valuable genetic resources to develop novel drought tolerance cultivars or for production in dry agro-ecologies of sub-Saharan Africa characterized by pre-and-post anthesis drought stress. In the third chapter, diversity arrays technology (DArT) –derived single nucleotide polymorphism (SNP) markers were used to assess the genetic diversity and discern the population structure of 200 sorghum accessions to select complementary lines for breeding. The markers have moderate discriminatory power, with the polymorphism information content ranging between 0.09 to 0.38. The average gene diversity value (0.32) was high, while the average observed heterozygosity (0.15) was relatively low, a typical value for autogamous crop species like sorghum. The population structure and cluster analyses revealed four main clusters with a high level of genetic diversity among the accessions studied. The variation within populations (41.5%) was significantly higher than that among populations (30.8%) and between samples within a structure (27.7%). The high genetic variation within the population could be attributed to the preservation of sorghum landraces by farmers and differences in the genetic constitution, adaptation and parentage. The study identified distantly related sorghum accessions such as Samsorg 48, Kaura Red Glume (from Cluster 1); Gadam, AS 152 (Cluster 2); CSRO1, ICNSL2014−062 (Cluster 3); and Yalai, Kafi Mori (Cluster 4) useful in developing new gene pools and novel genotypes for the West and Central Africa (WCA) sorghum breeding programs. Based on the phenotypic and genotypic data, 12 contrasting parents were selected for breeding population development with high yield and drought tolerance. In the last chapter, 12 contrasting sorghum parents were selected from a diverse set of 225 genotypes exhibiting variable agronomic traits, including high grain and drought tolerance and farmer-preferred attributes. The 12 parents were crossed using a half-diallel mating design to create 66 F1 progenies. The F1 progenies, the parents, and two check varieties were evaluated under three environments in Nigeria. The results revealed the presence of significant variations amongst test genotypes allowing the selection of suitable parents and hybrids for traits of interest. The contribution of the specific combining ability (SCA) variance to total variance was higher than that of the general combining ability (GCA) for most of the studied traits, indicating that nonadditive gene action was more dominant in conditioning trait inheritance. GCA x environment and SCA x environment interaction effects were significant (p<0.05) for days to anthesis, aboveground biomass and grain yield. Parental genotypes Samsorg 7, Masakwa, and SSV2008091, recorded significant and positive GCA effects for grain yield and are useful germplasm resources for breeding high-yielding cultivars. Crosses AS 152 x SSV2008091, Samsorg 7 x Kurumbasau, AS 152 x ICNSL2014-022-8, and Masakwa x Hindatu exhibited high and positive SCA effects and were the top performers recording above-ground biomass yield of 29.3, 23.4, 27.2 and 16.5 t/ha and grain yield of 6.4, 6.6, 6.6 and 6.5 t/ha, in that order. The crosses exhibited high parent heterosis for grain yield and other agronomic traits, revealing that hybrid breeding is an effective strategy for boosting sorghum production. The newly selected F1 progenies had higher yields than the local checks and are recommended for hybrid or pure line breeding and variety release in Nigeria's drought-prone areas and similar sub-Saharan Africa (SSA) agro-ecologies after continuous selection and multi-environment testing. Overall, the study identified drought stress as the most critical sorghum production constraint in Northern Nigeria. Also, the study highlighted significant genetic diversity among the test genotypes. Best performing genotypes Yar Lazau, ICNSL2014-022-4 and Danyar Bana were selected as suitable for non-stressed, pre-anthesis and post-anthesis drought stress conditions, respectively. The selected genotypes are recommended for production or breeding in droughtprone areas. In addition, the study identified drought-tolerant and early-maturing genotypes (e.g., Samsorg 7, Masakwa, and SSV2008091) with good general combining ability effects for breeding population development and heterosis breeding in the semi-arid region of Northern Nigeria. IQOQA Amabele [Sorghum bicolor (L.) Moench] iyisivuno sokudla okuyinhloko esiphakela izigidi zabantu e-Afrika kanye ne-agro-ecologies eyomile necishe koma yase-Asia. Amabele atshalwa kakhulu eNyakatho yeNigeria, asetshenziselwa uchungechunge lwezinto ezahlukahlukene, kufaka phakathi imikhakha yokudla kanye nomkhakha wokuphiswa kotshwala. Kodwa-ke, ukukhiqizwa okungenzeka kanye nomkhiqizo wamabele e-Afrika, kufaka phakathi iNyakatho yeNigeria, kucindezelwa ukucindezeleka okukhulu kwesomiso okuhambisana nokuguquka kwesimo sezulu. Ngaphezu kwalokho, abalimi abancane eNigeria basalima amabele akhiqiza kancane nesezindaweni ezizwelayo esomisweni. Ukuthuthukisa kokutshalwa kohlobo lwamabele abekezelela isomiso ezifundeni ezomile kungathuthukisa ukuzuza kwesivuno nokuzinza ngamaphrofayili omkhiqizo ofiselekayo ngokwezidingo zabalimi kanye nendawo yemakethe. Izinhloso ngqo zalolu cwaningo zazithi: (1) ukwethula amathuba amanje kanye nezingqinamba zokukhiqiza amabele eNigeria futhi wenze izincomo njengesiqondiso sokuklama izinhlobonhlobo ezintsha kanye nokukhiqizwa okuqhubekayo, (2) ukunquma ukubekezelela isomiso kanye nomphumela wokusebenzisana kwegenotype-by-environment (GEI) ekuvuneni okusanhlamvu kwabantu be-African sorghum genotypes ukuhlonza amagenotypes aphezulu futhi avumelaniswe nesomiso sokukhiqiza nokuzala, (3) ukuhlola ukuhlukahluka kwezakhi zofuzo nokuthola isakhiwo sokusabalala phakathi kokufinyelela kwamabele angama-200 ukuqondisa ukukhethwa kwabazali abahlukile bokuzalanisa kwangaphambili nokuzalanisa amacultivars amabele abekezelela isomiso futhi (4) ukunquma ikhono lokuhlanganisa, iheterosis kanye nesenzo segene esilungisa izici ze-agronomic kanye nesivuno sokusanhlamvu phakathi kwamagenotypes amabele ukukhetha amagenotypes aphakeme ngofuzo futhi ahlukile wabazali kanye nemindeni emisha yokuzalanisa ukubekezelelana kwesomiso, ukukhululwa kwecultivar nokuthengisa. Esahlukweni sokuqala, ucwaningo lwe- participatory rural appraisal (PRA) lwenziwe ezindaweni ezintathu ezikhethiwe zokukhulisa amabele eNyakatho yeNigeria ezibandakanya abalimi abanga-250. Imininingwane yezenhlalo nezomnotho yaqoqwa ngokusebenzisa inhlolovo kanye nezingxoxo zeqembu lokugxila. Imiphumela ikhombise ukuthi amabele alinywa ikakhulukazi ngabesilisa (80%) ababenezinga lemfundo lebanga le-6-12 (31.3%), abaneminyaka ekhiqizayo yeminyaka engama-21-45 (75.7%) kanye nobukhulu bomndeni wasekhaya obungaphansi kwamalungu amahlanu (52.3%). Izinhlobo zomhlaba ezithela kancane ezifana neKaura (37.4%) neFara-fara (29.3%) zaziyizinhlobo ezitshalwa kakhulu kuzo zonke izindawo zokufunda ngenxa yekhwalithi yazo enhle yokusanhlamvu. Izici ezikhethiwe zabalimi abakhulu ezivela ezinhlobonhlobweni zamabele zaziyisivuno esiphezulu, ukubekezelela isomiso nokumelana neStriga. Ucwaningo luncoma ukuthuthukiswa kobuchwepheshe obuhlanganisiwe bamabele okufaka izintandokazi ezichaziwe zabalimi zokukhiqiza okuqhubekayo kanye nokuzuza kwezomnotho kwesivuno. Isahluko sesibili sihlole amagenotypes anga-225 amabele ahlanganiswe kusuka ezimvelaphini ezahlukahlukene ukunquma ukubekezelela isomiso nemiphumela ye-GEI ekuvuneni okusanhlamvu. Amaqoqo ahlolwe ngaphansi kwezimo ezingacindezelekile, ezinon-stressed (NS), ukucindezeleka kwesomiso sangaphambi kwe-anthesis, ipre-anthesis drought stress (PreADS), kanye nepost-anthesis drought stress (PoADS) ngaphansi kwezindawo zensimu kanye negreenhouse. Umphumela oyinhloko wesengezo kanye nokuhlaziywa kokusebenzisana kwemultiplicative (AMMI) kuveze ukuthi igenotype (G), imvelo okuyi-environment (E), ne-GEI yayibalulekile (p<0.05) futhi yaba ngama-38.7, 44.6, ne-16.6% wokuhlukahluka okuphelele okuchaziwe kwesivuno sokusanhlamvu, ngaleyo ndlela. I-AMMI 4 yayiyimodeli efaneleka kakhulu yokukhethwa kwegenotype ngesivuno esingcono sokusanhlamvu. Ngokusekelwe ekuhlaziyweni kwe-AMMI 4 kanye neBest Linear Unbiased Predictors (BLUPs), amagenotypes uYari Lazau noDangama Wulchichi, ngesivuno sokusanhlamvu se-5.6 t / ha ne-6.3 t / ha, bakhethwa njengabafanele izimo ezingacindezelekile, ngokulandelana. IGenotypes ICNSL2014-022-4 neTakumbo enama-BLUP we-2.5 t / ha ne-2.6 t / ha yayilungele kakhulu izimo zokucindezeleka kwesomiso sangaphambi kwe-anthesis, kanti amagenotypes Danyar Bana noGagarau - 4 nge-BLUPs ye-4.2 t / ha ne-4.3 t / ha kunconywa ezindaweni ezithambekele esomisweni ngemuva kwe-anthesis, ngokulandelana. Igenotypes yamabele ehlonziwe iyimithombo yofuzo eyigugu ukuthuthukisa amacultivars okubekezelela isomiso senoveli noma ukukhiqizwa kuma-agro-ecologies omile e-Afrika engezansi kweSahara ebonakala ngokucindezeleka kwesomiso sangaphambi kokuthunyelwe kwe-anthesis. Esahlukweni sesithathu, idiversity arrays technology (DArT) – nezimpawu amaderived single nucleotide polymorphism (SNP) kwasetshenziselwa ukuhlola ukuhlukahluka kwezakhi zofuzo nokuqonda isakhiwo senani sokufinyelela kwamabele okungama-200 ukukhetha imigqa ehambisanayo yokuhiqiza. Izimpawu zinamandla okubandlulula ngokulinganisela, ngokuqukethwe kolwazi lwepolymorphism okuphakathi kuka-0.09 kuya ku-0.38. Inani elijwayelekile lokuhlukahluka kwezakhi zofuzo (0.32) laliphezulu, kanti isilinganiso sabona iheterozygosity (0.15) yayiphansi kakhulu, inani elijwayelekile lezinhlobo zezitshalo ze-autogamous njengamabele. Isakhiwo senani kanye nokuhlaziywa kweqoqo kwaveza amaqoqo amane aphambili anezinga eliphezulu lokuhlukahluka kwezakhi zofuzo phakathi kokufinyelela kokufundiwe. Ukuhlukahluka ngaphakathi kwenani (41.5%) kwakuphakeme kakhulu kunalokho phakathi kwenani (30.8%) naphakathi kwamasampula ngaphakathi kwesakhiwo (27.7%). Ukuhlukahluka okuphezulu kwezakhi zofuzo ngaphakathi kwenani kungabangelwa ukulondolozwa komhlaba wamabele ngabalimi kanye nokwehluka komthethosisekelo wofuzo, ukuzivumelanisa nezimo kanye nokuba ngumzali. Ucwaningo luveze ukufinyelela kwamabele okuhlobene kude njengeSamsorg 48, i-Kaura Red Glume (kusuka ku-Cluster 1); Gadam, AS 152 (Cluster 2); CSRO1, ICNSL2014−062 (Cluster 3); noYalai, uKafi Mori (Cluster 4) owusizo ekuthuthukiseni amachibi amasha ezakhi zofuzo kanye namagenotypes amasha ezinhlelo zokuzalanisa amabele zaseNtshonalanga naphakathi ne-Afrika (WCA). Ngokusekelwe emininingweni yephenotypic negenotypic, abazali abayi-12 abaphikisanayo bakhethwa ukuthuthukisa inani lesivuno esiphezulu nesinokubekezelela isomiso. Esahlukweni sokugcina, imithombo eyi-12 eyahlukene yamabele yakhethwa esethini ehlukahlukene yamagenotypes anga-225 abonisa izici eziguquguqukayo ze-agronomic, kufaka phakathi okusanhlamvu okuphezulu nokubekezelela isomiso kanye nezici ezikhethiwe zomlimi. Imithombo eyi-12 yaxutshwa kusetshenziswa umklamo wokukhwelana wesigamu sediallel ukudala inzalo ye-66 F1. Inzalo ye-F1, imthombo, kanye nezinhlobo ezimbili zokuhlola zahlolwa ngaphansi kwezindawo ezintathu eNigeria. Imiphumela yaveza ukuba khona kokuhlukahluka okuphawulekayo phakathi kwamagenotypes okuhlola okuvumela ukukhethwa kwemithombo efanelekayo kanye namahybrid ezici ezithakazelisayo. Umnikelo ispecific combining ability (SCA) ukuhlukahluka kokuhlukahluka okuphelele kwakuphakeme kunalokho kwekhono igeneral combining ability (GCA) iningi lezici ezifundiwe, okubonisa ukuthi isenzo segene esingangeziwe sasibusa kakhulu esimweni sefa lesici. I-GCA x imvelo kanye ne-SCA x imvelo kwakubalulekile (p<0.05) ezinsukwini kuya ku-anthesis, ngaphezu kwebiomass yomhlaba kanye nesivuno sokusanhlamvu. Amagenotypes awumthombo i-Samsorg 7, i-Masakwa, ne-SSV2008091, aqophe imiphumela ebalulekile futhi emihle ye-GCA yesivuno sokusanhlamvu futhi ayimithombo ewusizo yegermplasm yokuzalanisa amacultivars aphezulu. Ukuxutshwa kwe-AS 152 x SSV2008091, i-Samsorg 7 x Kurumbasau, i-AS 152 x ICNSL2014-022-8, ne-Masakwa x Hindatu kubonise imiphumela ephezulu futhi emihle ye-SCA futhi yayingabadlali abaphezulu abaqopha isivuno se-biomass esingaphezulu komhlaba we-29.3, 23.4, 27.2 ne-16.5 t / ha kanye nesivuno sokusanhlamvu se-6.4, 6.6, 6.6 no-6.5 t / ha, ngaleyo ndlela. Ukuxuba kwabonisa iheterosis ephezulu yomthombo wesivuno sokusanhlamvu nezinye izici ze-agronomic, eveza ukuthi ukuzalanisa ihybrid kuyindlela ephumelelayo yokukhulisa ukukhiqizwa kwamabele. Inzalo esanda kukhethwa ye-F1 yayinesivuno esiphezulu kunokuhlolwa kwendawo futhi inconywa ukuzalanisa umugqa wehybrid noma ohlanzekile kanye nokukhishwa kwezinhlobonhlobo ezindaweni zaseNigeria ezithandwa isomiso kanye ne-agro-ecologies efanayo yesub-Saharan Africa (SSA) ngemuva kokukhethwa okuqhubekayo nokuhlolwa kwemvelo eningi. Sekukonke, ucwaningo lwaveza ukucindezeleka kwesomiso njengengcindezi ebucayi kakhulu yokukhiqiza amabele eNyakatho Nigeria. Futhi, ucwaningo lwaqhakambisa ukuhlukahluka okuphawulekayo kwezakhi zofuzo phakathi kwamagenotypes okuhlola. Amagenotypes enza kahle kakhulu uYar Lazau, ICNSL2014-022-4 noDanyar Bana akhethwa njengafanelekile ezimweni zokucindezeleka ezingacindezelekile, zangaphambi kwe-anthesis kanye nezimo zokucindezeleka kwesomiso ngemuva kwe-anthesis, ngokulandelana. Amagenotypes akhethiwe anconywa ukukhiqizwa noma ukuzala ezindaweni ezithambekele esomisweni. Ngaphezu kwalokho, ucwaningo lwaveza amagenotypes abekezelela isomiso futhi avuthwa ekuqaleni (isib., iSamsorg 7, iMasakwa, ne-SSV2008091) ngemiphumela emihle ejwayelekile yokuhlanganisa ikhono lokuthuthukiswa kwenani elizalayo kanye nokuzalanisa iheterosis esifundeni esomile saseNyakatho Nigeria.
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    Breeding investigations for developing durable resistance to maize lethal necrosis disease (MLND) and its causal viruses in Kenya.
    (2021) Karanja, James Kamau.; Derera, John.; Gubba, Augustine.; Mugo, Stephen.; Wangai, Ann.
    Maize is an important staple food in Kenya, grown in almost all agro-ecological zones, and accounts for about 40% of daily calories. The country produces an average of 3.51 million tons of maize grain (39 million x 90 kg-bags) which does not match the demand. The production is limited by emerging pests and diseases, such as fall army worm (FAW) and maize lethal necrosis (MLN) disease. The MLN disease is caused by synergisim between maize chlorotic mottle virus (MCMV) and sugar cane mosaic virus (SCMV). The FAW and MLN cause serious challenges for maize production due to the lack of suitable cultural control methods and tolerant maize germplasm. As a result, farmers and government agencies have challenged maize breeders to develop varieties that are resilient to climage change. This study focused on breeding investigations for developing durable resistance to maize lethal necrosis disease and its causal viruses in Kenya. The specific objectives were to 1) identify maize germplasm lines that are tolerant to MLN and its causative viruses (SCMV and MCMV) for use in making hybrid combinations; 2) to understand the genetic divergence and background of these genotypes to aid in developing high yielding and stable MLN resistant maize hybrids; and 3) to assess the impact of MLN, SCMV, and MCMV on maize production in Kenya. Experiments were conducted in Kenya during the 2015, 2016, 2017 and 2018 seasons in both screen house and open fields. Diallel crosses were used to characterize maize inbred lines, from CIMMYT, KALRO, and Ohio, for reactions to SCMV, MCMV and MLN disease. A set of selected and pre-commercial maize hybrids were used to assess MLN impact on maize production in Kenya. The study revealed that MLN is important for maize production, with high incidence and severity levels observed in all commercial maize varieties in Kenya. Disease severity, yield and its attributes significantly varied (P < 0.05) at V3, V7 and VT inoculation stages. The greatest effect was observed at V3 stage with increased number of rotten cobs observed at VT. Percentage yield loss was proportional to the percentage of disease incidence, severity and effect on yield attributes which varied from variety and season. This calls for the development and deployment of improved maize hybrids with MLN tolerance/resistance in the MLN-prone areas to enhance maize production. The study further identified eight inbred lines with low disease severity < 3.0 at 56dpi indicating their tolerance/resistane to SCMV, MCMV and MLN. The maize inbred lines MLN001 and MLN006, displayed high levels of resistance to MCMV, while MLN042 and MLN041 had the highest resistance to SCMV. Strong sources of MLN resistance, such as MLN013, MLN019, N211, and KS23-6, should be used in developing MLN-resistant hybrids. Inbred lines CML312, CML442, MLN013, N211 and MLN 019 are identified as good combiners for yield and earliness. The nature of gene effects was established as one including additive, and that genotype x location effects were significant for conditioning MLN resistance in maize hybrids. The presence and impact of SCMV and MCMV viruses in the field need to be investigated to aid in developing more robust MLN resistant varieties. MNL001, MLN013, MLN018, and MLN019 and their derived crosses need to be evaluated across maize agro-ecologies and seasons to understand MLN disease, the role of environment and the interaction of MCMV and Potyviruses.
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    Improving dry beans (phaseolus vulgaris L.) of middle American gene pool for canning and nutritional quality traits, and drought tolerance in Zimbabwe.
    (2022) Mutari, Bruce.; Sibiya, Julia.; Gasura, Edmore.
    Among the different dry beans market classes, navy bean is a modern and specialised niche market-oriented product for domestic and foreign markets. Given the high navy bean import bill, increased prevalence of drought, and micronutrient malnutrition in Zimbabwe, the development of drought tolerant, high yielding and biofortified bean cultivars with superior canning quality offers a sustainable solution to the aforementioned challenges. Therefore, the objectives of this study were: (1) to identify farmers’ perceived production and marketing constraints, preferred traits and cultivars of navy bean, and strategies used to mitigate drought and heat stress in the south east lowveld region of Zimbabwe, (2) to evaluate the adaptability and stability of navy bean genotypes for grain yield and nutritional quality traits (Fe and Zn) across multiple locations in Zimbabwe, (3) to investigate the impact of drought stress on agronomic, shoot, physiological, canning and nutritional quality traits of navy beans, and identify drought tolerant genotypes with superior canning and nutritional quality, (4) to determine combining ability effects and mode of gene action of grain yield and yield-attributing traits in navy bean under drought stressed and non-stressed environments and select best combiners for effective breeding, (5) to quantify genome-wide marker-trait association of agronomic and physiological traits in dry beans under non-stressed (NS) and drought stressed (DS) conditions and to identify candidate markers for marker-assisted selection (MAS). A participatory rural appraisal (PRA) study conducted in four villages of the Lowveld region of Zimbabwe showed that the most important constraints to navy bean production were drought stress (79.5%), heat stress (56.5%), load shedding (50%), susceptibility to pod shattering (37.5%) and poor soil fertility (32.5%). Farmer-preferred traits included tolerance to drought and heat, early maturing varieties and disease resistance. Marketing constraints included nonpayment for produce in hard currency, lack of diversity in terms of off-takers, high inflation, low grain producer price, and delayed payment. Suggested mitigation strategies were mulching (18%), ridges (12%), reduced acreage (11%), and cultivating to retain more soil moisture (11%) for drought stress, while irrigating at night (32%), and adjusting planting dates (29%) were used to manage heat stress. A study on the evaluation for adaptability and stability of 84 navy bean genotypes for grain yield (GYD), seed Fe and seed Zn across four locations over two seasons in Zimbabwe was done using additive main effects and multiplicative interaction (AMMI), AMMI stability value (ASV) and yield stability index (YSI). This resulted in the identification of six genotypes (G14, G49, G37, ICA BUNSIxSXB405/3C-1C-1C-8, NAE70 and CZ108-53) with high GYD, good GYD stability and desirable seed Fe and Zn concentrations above breeding targets of 90 and 40 ppm, respectively. The vertex genotypes ZABRA16575-26F22, ICA BUNSIxSXB405/4C-1C-1C-8 and NAE13 combined specific adaptation and high GYD with desirable micronutrient density. Furthermore, the impact of drought stress on agronomic and shoot traits, canning and nutritional quality of navy beans was conducted on 110 navy bean genotypes in 2019 and 2020 at Save Valley Experiment Station, Zimbabwe under drought stressed (DS) and non-stressed (NS) field conditions. Across environments, the genotype effect on agronomic, shoot, physiological, canning and nutritional quality traits was significant (p < 0.001; p < 0.05). Broad-sense heritability estimates were high for all canning quality traits and moderate to high for most agronomic and nutritional quality traits. Under DS conditions, the predicted genotype values (Ĝ) for seed micronutrient concentrations ranged from 72.3 (NAVY LINE-48) to 120 ppm (ZABRA16575-51F22) for Fe, 31.3 (NAVY LINE-46) to 60.8 (NAE70) for Zn, while washed drained weight (WDW) varied from 224.8 (Protea) to 310 (G24), and GYD ranged from 494 (SIRAJ) to 2619 kg/ha (ZABRA16573-78F22). Terminal drought stress reduced mean stomatal conductance (SC), leaf chlorophyll content (LCC), GYD, number of mature pods per plant, number of seeds per pod, number of seeds per plant and 100-seed weight by 80, 42, 28, 26, 3, 30 and 3%, respectively. Seed Fe concentration and leaf temperature (LT) increased by 1.4% and 34% in the DS environments, respectively, whereas seed Zn decreased by 0.9%. Terminal drought stress adversely impacted the canopy biomass, pod harvest index, hydration coefficient, WDW, uniformity, shape of seed and degree of splitting. The effect of DS was less severe on the degree of clumping and percent washed drained weight. ZABRA16575-86F22 had better mean ranks across four GYD based drought tolerance indices, canning and nutritional quality traits under DS compared to the standard checks. Combining ability analysis of 28 F2 progenies generated from an 8 x 8 half-diallel mating design and evaluated under DS and NS conditions resulted in significant general and specific combining ability (GCA; SCA) effects (p < 0.05) under both DS and NS for most traits. This indicated the importance of both additive and non-additive gene effects in the expression of the traits. Parents with best GCA for most of the studied traits were CZ113-13, G97, NAVY LINE-60, and G550 under NS, and ZABRA16575-73F22, G37, G97 and G550 under DS. ZABRA16575-73F22 and NAVY LINE-60 were tolerant to DS with high values for drought tolerance index (DTI) and geometric mean productivity (GMP) and low values for percentage grain yield reduction (%GYR) and drought susceptibility index (DSI). There were significant (p < 0.001; p < 0.05) positive correlations for number of pods per plant (NPPP) and 100-seed weight (SW; g) with GYD under both DS and NS. Using an andean and middle-american diversity panel (AMDP) comprising of 185 dry beans genotypes, genome-wide marker-trait association analysis of agronomic and physiological traits in dry beans under DS and NS conditions was conducted. Genotyping was done using 24,450 Diversity Arrays Technology (DArT) markers, while the following traits: days to 50% flowering (DFW), plant height (PH), days to physiological maturity (DPM), grain yield (GYD), 100-seed weight (SW), leaf temperature (LT), leaf chlorophyll content (LCC) and stomatal conductance (SC) were recorded. Principal component and association analysis were conducted using filtered 9370 DArTseq markers. Population structure analysis revealed two sub-populations, which correspond to the andean and middle-american gene pools. Markers explained 0.08 – 0.10, 0.22 – 0.23, 0.29 – 0.32, 0.43 – 0.44, 0.65 – 0.66 and 0.69 – 0.70 of the total phenotypic variability (R2) for SC, LT, PH, GYD, SW and DFW, respectively under DS conditions. A total of 68 significant (p < 10-03) marker-trait associations (MTAs) and 22 putative candidate genes were identified under contrasting water regimes. Most of the identified genes had known biological functions related to regulating drought stress response, growth and development under drought stress. In conclusion, the identified farmer-preferred traits, marketing, and production constraints should be considered by the breeding programme in Zimbabwe during the development of improved cultivars. Stable genotypes identified to be drought tolerant and to possess desirable micronutrient density, superior canning and nutritional quality should be used as parents for crossing with other cultivars to improve micronutrient density, GYD and GYD stability and also recommended for deployment in their respective mega-environments. Good general and specific combiners with desirable values of drought tolerance indices and high significant positive effects under DS should be used further in breeding for drought stress tolerance. The identified markers should be validated for use in marker-assisted breeding for drought tolerance.
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    Developing pre-breeding tools for the miracle plant [Synsepalum dulcificum (Schumach & Thonn.) Daniell]: implications for genomic selection strategies optimization = Ukuthuthukisa amathuluzi okuzalanisa ngaphambilini esitshalo esiyisimangaliso [Synsepalum dulcificum (Schumach & Thonn.) Daniell]: imithelela yokuthuthukisa amasu okukhetha i-genomic.
    (2022) Tchokponhoué, Dèdéou Apocalypse.; Sibiya, Julia.; Achigan-Dako, Enoch Gbenato.
    The miracle plant [Synsepalum dulcificum (Schumach & Thonn) Daniell] is an evergreen orphan shrub species originating in West Africa that produces red berries known as miracle fruits. As a unique natural source of miraculin, miracle fruits stand as a singular natural sweetener with huge applications and economic potential. Unfortunately, the lack of systematic breeding history in the species currently hinders the full exploitation of the species potential at both the local and international levels. This study was undertaken with the goal of generating information that can be used to initiate a proper breeding and large-scale cultivation program of the species in its center of origin, West Africa, with a focus on three countries (Ghana, Togo, and the Republic of Benin). The objectives of the study were: i) to determine current management practices and end-users’ preferred traits to identify key breeding traits and formulate sound breeding objectives, ii) to evaluate the natural phenotypic diversity in the species to identify potential parental lines/populations for breeding purposes, to assess genomic diversity and population structure in the species to reshape breeding strategies, and to model the determinants of the local communities’ willingness to invest in the species cultivation to articulate promotion strategies in the species. To assess trait preferences by the miracle plant end-users (farmers, consumers, and processing companies) in the study area, semi-structured interviews and focus-group discussions were held with 300 individual respondents from various socio-cultural backgrounds and one processing company each in Benin and Ghana. The results revealed that farmers in Ghana currently manage the species better than their counterparts in Benin, with men being overall the main owners of the species. Our results offer an impetus for West Africa region-wide cultivar development, as both farmers’ and consumers’ preferences for breeding traits were >80% similar among the six sociolinguistic groups and the three agroecological zones considered in the study area. The preference for breeding traits was 60% similar among farmer, consumer and processing company user groups. Out of the 23 potential breeding traits identified in the study area, fruit size, fruit miraculin content, fruit yielding, early maturity, fruit edible ratio and seed part ratio represent priority breeding traits. Interestingly the traits (fruit size and miraculin content) were consistently ranked as the top two desired traits by all three end-user groups of the species. The classification conducted on 203 individual trees (accessions) sampled from seven populations in the Upper Guinea forest block (Ghana) and the Dahomey Gap (Ghana, Togo, and Benin) block revealed the existence of three natural phenotypic groups in the species. While in terms of population performance, the Volta population in the Dahomey Gap outperformed the six other populations for almost all the end-users’ desired traits assessed. Cluster 3, which encompassed accessions from all seven populations sampled, presented the best performance based on end-users’ preferences and, therefore, represents a potential source of elite accessions. Overall, variability ranged from low to moderate in traits evaluated [coefficient of variation: 9.65% (fruit length) – 53.34% (tree diameter at ground level] and the inferred core collection points to the Dahomey Gap as a center of diversity of the miracle plant. Despite the expected heterozygosity of HS = 0.14 suggesting a low diversity in the miracle plant, the molecular assessment done on 322 individuals revealed a strong population differentiation in the species (FST =0.69). Populations in the Upper Guinea forest block strongly diverged from those in the Dahomey Gap block, and our data supported the existence of a barrier (which we speculated to be the Lake Volta in Ghana) disrupting connectivity between those two West African rainforest block populations of the miracle plant. Corroborating the findings of the phenotypic assessment, the genome-wide diversity analysis also defined three genetic groups. Conveying a higher resolution to the population structuring, the genomic analysis highlighted an ecoregional structuring of the miracle plant population in the study area. The DNA polymorphism and demographic history analyses indicated the Western Dahomey Gap as the likely centre of origin of the miracle plant, thus refining the previously postulated West Africa origin of the species. The Volta population was confirmed as an exceptional breeding population with regards to its high allelic richness and heterozygosity. Our findings also suggest that sociolinguistic groups in Benin valued the miracle plant more than those in Ghana, to the extent that the species diversity was affected, as fitness organs such as roots and bark were highly targeted for medicinal uses. Nonetheless, these sociolinguistic groups in Benin were also more willing to engage in the miracle plant cultivation compared with those in Ghana. However, for this to be effective, market structuring and improved variety (early fruiting) development combined with awareness raising are needed to accelerate local community engagement in the species cultivation in the entire study area. Collectively, these results advance our knowledge of the miracle plant and form the basis for breeding initiatives in the species. The implications of these findings regarding optimization of a genomic selection strategy for accelerated genetic gains achievement in agronomic and functional traits of this species is discussed. Iqoqa Isitshalo esiyisimanga [Synsepalum dulcificum (Schumach & Thonn.) Daniell] wuhlobo lwembewu yesihlahla esingavamile esidabuka eNtshonalanga ne-Afrika, esaziwa ngokuthi siwumsuka ohlukile wemiracuin, isinandisi seglycoprotein esisetshenziswa ngezindlela ezahlukene. Yize kunjalo ukugqama kwaso kahle kukhinyabezwa ukungabi bikho kokuchuma kahle kwaso emlandweni wezimbewu. Lapha, injulalwazi emgwaqohlaka onezigaba zokuzalana kwale mbewu kuyacaciswa kanye nokubaluleka kokugxila esizindeni sokuqoqa ukuthuthuka kwaso ngenhloso yokuqondisisa, kwavezwa. Indlela enokubambisana yasetshenziswa ukuhlonza ubukhulu balesi sithelo, okuqukethwe yisithelo okuyimiraculin, ukuthela kwesitshalo, inani lokukhula kwesithelo, ukuvunwa kwesithelo singakashayi isikhathi, impilo yesitshalo eshalofini, kanye nobuncwaba besithelo njengezinto ezinqala ezidingeka ezitshalweni kulabo abazisebenzisayo eNtsonalanga ne-Afrika. Kwaqapheleka izinga eliphezulu elincamelekayo elifanayo lembewu, hhayi nje kuphela kubatshali, kepha nakubathengi bezitshalo ezahlukene ze-agroecological zones nakulabo abavela kwizindawonhlalo zolimi olwahlukene. Amaqoqo amathathu afanayo acwaningwa kulesi sitshalo eNtshonalanga ne-Afrika, kuphindelelwa ukusebenza kwaso kusezingeni eliphezulu u-0.8. Imiphumela yaveza iDahomey Gap njengomongo wokwehluka kwembewu. Le mininingo efuzene ibe isifakazelana ngesingle nucleotide polymorphism (SNP) markers eyizi-2704 iyinye. Yize-ke noma ukwehluka kwamamolekhyuli kube sezingeni eliphansi embewini (He = 0.14), kwase kuqina ukwehluka emiphakathini phakathi kwe-upper Guinea kanye neDahomey Gap, lokhu kwaze kwafakazelwa ukuhlaziywa KOHLAKA, okwaqagula ulibofuzo oluthathu esixhokweni esihambelana ne-Upper Guinea (UG), neWestern Dahomy Gap (WDG) neCentral Dahomy Gap (CDG). Imiphumela yethu yeseka umlando oguqukayo kulolu libofuzo lapho khona imiphakathi ye-UG ne-CDG kungenzeka ithole ukunwebeka kanti i-WDG iphakathi nendawo. Ekugcineni, yize noma imbewu yayiningi eGhana uma iqhathaniswa neBenin, amaqoqo enhlalolimi eBenin ayikhathalele imbewu kakhulu kunalabo baseGhana. Ulwazi olumangazayo ngembewu nobukhona bohwebo kuqaguleke njengezinye zezinto ezilawula inhlalosiko yokutshalwa kwale mbewu eNtshonalanga ne-Afrika. Le miphumela yethula ulwazi olubalulekile olungasetshenziswa ezinhlelweni zokuzalaniswa kwembewu.
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    Breeding for high leaf yield and minerals content in Gynandropsis gynandra (L.) Briq.
    (2022) Houdegbe, Aristide Carlos.; Sibiya, Julia.; Achigan-Dako, Enoch Gbenato.
    Gynandropsis gynandra (Spider plant) is an African leafy vegetable rich in minerals, vitamins, and health-promoting compounds with great potential in addressing malnutrition. The species is used as food and medicine and provides substantial incomes for smallholder’s farmers with an increasing interest for its cultivation in Africa. Spider plant is also an important resource for pharmaceutical industries. However, its production is still hampered by low leaf yield, early flowering, pests and disease and poor seed germination, resulting from the lack of improved cultivars. Our study intended to develop high yielding and nutrient-dense cultivars for farmers through merging modern molecular and classical plant breeding tools to increase income generation and improve nutrition and health. Specifically, the study: i) assessed the phenotypic variability among advanced lines of spider plant using biomass and related traits; ii) profiled the leaf mineral content among advanced lines of G. gynandra; iii) determined the combining ability, gene action and heterosis of mineral content in spider plant; iv) identified the genetics of the inheritance of biomass and related traits in spider plant; and v) deciphered genomic regions associated with combining ability and heterosis of biomass and related traits in G. gynandra. The evaluation of 71 advanced lines of spider plant derived from accessions originating from Asia, East, Southern and West Africa using biomass and related traits revealed significant difference among lines and principal component analysis grouped them into three clusters: Asia (Cluster 1), West Africa (Cluster 2), and East/Southern Africa (Cluster 3). The West and East/Southern African groups were comparable in biomass productivity and superior to the Asian group. Specifically, the West African group had high dry matter content and flowered early while the East/Southern African group was characterized by broad leaves and late flowering. The maintenance of lines’ membership to their group of origin strengthens the hypothesis of geographical signature in cleome diversity as genetic driver of the observed variation. The leaf mineral profile of 70 advanced lines of spider plant derived from accessions originating from Asia, East, Southern and West Africa revealed significant variation among lines and zinc, calcium, phosphorus, copper, magnesium, and manganese as landmark elements in the genotypes. East and Southern African genotypes were clustered together in group 1 with higher phosphorus, copper and zinc contents than Asian and West African lines, which clustered in group 2 and were characterized by higher calcium, magnesium and manganese contents. An additional outstanding group 3 of six genotypes (three, two, and one from Asia, Southern Africa and Eastern Africa, respectively) was identified with high iron, zinc, magnesium, manganese and calcium contents and potential candidates for cultivar release. Significant differences (P < 0.001) were observed among and between experimental hybrids and parents for the levels of all mineral contents. Significant general and specific combining ability effects together with variance components analysis revealed that both additive and nonadditive gene action controlled mineral content with a predominance of nonadditive gene action. Mid- and best-parent heterosis ranged from -84.98 and 404.79% for minerals. Parents with good general combining ability were identified, as well as crosses with high specific combining ability and heterosis. There were significant and moderate to strong correlations between mean hybrid performance, specific combining ability effects and heterosis levels and low to moderate correlations between general combining ability and mean parents’ performance. Similar to leaf mineral content, significant differences (P < 0.001) were observed among and between hybrids and parents for fourteen agronomic traits. Hybrids outperformed their parents with more than 50% for total and edible fresh biomass, showing the existence of hybrid vigour. Mid- and best-parent heterosis varied between -51.89% and 192.10% with only positive heterosis effects for leaf area and total fresh biomass, characterized by an average mid-parent heterosis greater than 50%. Significant general and specific combining ability (GCA and SCA) effects together with variance component analysis revealed that both additive and nonadditive gene action, controlled biomass and related traits in the species with the predominance of additive gene action. Moderate to high broad- and narrow-sense heritability was observed for most agronomic traits, except for dry matter content. The environment significantly interacted with genotype, GCA and SCA. Parents with good GCA and crosses with high SCA and heterosis were identified. There were significant changes from parents to hybrids in the association of harvest index and time to 50% flowering with biomass per plant and leaf traits on the one hand and between harvest index and dry matter content on the other hand. A core set of 594 diversity array technology sequencing (DArt-seq) markers were identified and differentiated the 38 parental lines into three clusters linked with the provenance of the original accession. Using this set of markers, a genome-wide association analysis revealed two markers linked to heterosis level for flowering time, a single marker for edible biomass, one marker for total fresh biomass and one marker for the number of primary branches. Specifically, the marker MABiomLa1 was a pleiotropic marker and was associated with heterosis level for biomass and leaf area. In contrast, no consistent markers associated with combining ability were observed for general combining ability and might be due to the low number of parents and the density of markers used. The study thus revealed that reciprocal recurrent selection would be a sound breeding strategy for G. gynandra improvement with the development of hybrid cultivars to exploit heterosis. These findings showed that G. gynandra could be used as a model plant to study the genetic mechanism underlying heterosis in orphan leafy vegetables. The identified markers open room for implementing marker-assisted selection in the species for better exploitation of heterosis.
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    Pre-breeding sesame (Sesamum indicum L.) for improved yield, and oil quality and quantity in Ethiopia = Ukuzalanisa kwangaphambili i-Sesame (Sesamum indicum L.) ukuze kuvunwe u-oyela okuthuthukisiwe, oyikhwalithi nomningi e-Ethiopia.
    (2022) Teklu, Desawi Hdru.; Shimelis, Hussein.
    ABSTRACT Pre-breeding Sesame (Sesamum indicum L.) for Improved Yield, and Oil Quality and Quantity in Ethiopia Sesame (Sesamum indicum L.; 2n = 2x = 26) is a multi-purpose industrial oilseed crop serving the food, feed, and cosmetic industries globally. Sesame is Ethiopia’s most valuable export crop after coffee (Coffea arabica L.), contributing to socio-economic development. However, the productivity of the crop is low (<0.6 ton ha-1) and stagnant in Ethiopia and other major sesame growing regions in sub- Saharan Africa due to a multitude of production constraints. The low yield of sesame is attributable to lack of high-yielding and well-adapted varieties, with less capsule shattering; resistant/tolerant to biotic and abiotic stresses; a lack of modern crop production technologies and well developed infrastructure. Sesame remains a largely under-researched and underutilized crop in Ethiopia despite its economic value in the local, regional and international trades. There is a need for a dedicated sesame genetic improvement programme to develop and deploy new improved varieties with farmer- and market-preferred traits. Therefore, the specific objectives of this study were: i) to document sesame production opportunities and constraints and farmer-and market-preferred varieties and traits in eastern and southwestern Ethiopia as a guide for breeding; ii) to determine the variance components, broad-sense heritability (h2b) and association of seed and oil yield-related traits in Ethiopian sesame germplasm for effective breeding; iii) to determine the extent of genetic variation among 100 diverse sesame germplasm collections of Ethiopia using phenotypic traits and simple sequence repeat (SSR) markers and select distinct and contrasting genotypes for breeding and iv) to determine the genetic diversity and relationships among Ethiopia’s sesame germplasm collections using seed oil content and fatty acid compositions and diagnostic SSR markers and select genetically unique and promising parental lines for breeding. Different but complementary research activities were conducted to attain the objectives. The first study was conducted using a participatory rural appraisal (PRA) involving 160 farmers in two selected sesame growing regions and four districts in Ethiopia. A considerable proportion of the respondent farmers (56.0%) reported cultivating sesame using seeds of unknown varieties often sourced from the informal seed sector. The most important constraints to sesame production in the study areas were lack of access to improved seeds (reported by 83.0% of respondents), low yield potential of the existing varieties (73.8%), diseases (69.4%), and low market price (68.8%). These constraints were attributed to the lack of a dedicated breeding programme, formal seed sector, strong extension services, and well-developed pre-and post-harvest infrastructures. The most important market-preferred traits of sesame included true-to-type seed, white seed colour, and high seed oil content. Reasonable market price, resistance to crop diseases, drought tolerance, resistance to crop insect pests, higher seed yield, higher thousand-seed weight, higher oil content, white seed colour, early maturity, and good oil qualities such as aroma and taste were the vital farmer-preferred attributes in order of significance. Hence, these traits should be integrated in current and future sesame breeding programs. The second study evaluated 100 sesame germplasm under field conditions at two locations using a 10 x 10 lattice design with two replications. The findings revealed a higher genotypic coefficient of variation and h2b values for the number of primary branches (NPB), number of secondary branches (NSB), thousand seed weight (TSW), seed yield per hectare (SYH) and oil yield per hectare (OYH), suggesting that high genetic gains can be achieved through selection. Higher direct effects of OYH and number of seeds per capsule (NSPC) were recorded affecting SYH, while SYH, number of capsules per plant (NCPP) and TSW had a higher direct effect on OYH. Genotypes Hirhir Kebabo Hairless-9, Setit-3, Orofalc ACC-2, Hirhir Humera Sel-6, Setit-1 and ACC-NS-007(2) were selected for further breeding based on their high seed yield, oil content and oil yield. In the third part of the study, 100 sesame entries were field evaluated at two locations in Ethiopia for agro-morphological traits and seed oil content using a 10 × 10 lattice design with two replications. Also, test genotypes were profiled using 27 polymorphic SSR markers at the Oil Crops Research Institute of the Chinese Academy of Agricultural Sciences. Analysis of variance revealed significant (p≤ 0.05) entry by environment interaction for plant height, internode length, number of secondary branches, and grain yield. Genotypes such as Hirhir Kebabo Hairless-9, Setit-3, Orofalc ACC-2, Hirhir Humera Sel-6, ABX = 2-01-2, and Setit-1 recorded grain yield of >0.73 ton ha−1. Grain yield had positive and significant (p < 0.01) associations with oil yield (r = 0.99), which is useful for simultaneous selection. Moderate gene diversity and polymorphic information content values of 0.30 and 0.25 were recorded based on SSR analysis, respectively. The genotypes were separated into two and four major distinct groups based on cluster and population structure analyses, respectively, thus enabling selection and subsequent crossing to develop breeding populations for cultivar development. Based on phenotypic and genomic divergence, the following superior and complementary genotypes were selected: Hirhir Humera Sel-6, Setit-3, Hirhir Kebabo Hairless Sel-4, Hirhir Nigara 1st Sel-1, Humera-1 and Hirhir Kebabo Early Sel-1 (from cluster II-a), Hirhir kebabo hairless-9, NN-0029(2), NN0068-2 and Bawnji Fiyel Kolet, (from cluster II-b). The selected genotypes will serve as parents for sesame breeding program in Ethiopia. Iqoqa I-Sesame (Sesamum indicum L.; 2n = 2x = 26) iyisitshalo sembewu kawoyela enezinhloso eziningi ephakela izimboni ukudla, izimboni eziphakelyo, nezimboni zezimonyo emhlabeni jikelele. I-Sesame iyisitshalo esiyigugu kakhulu sase-Ethiopia esithunyelwa ngaphandle ngemuva kwekhofi (i-Coffea arabica L.), esinegalelo ekuthuthukisweni kwenhlalakahle yezomnotho. Nokho, ukukhiqiza kwezitshalo kuphansi ngomklamo ka (<0.6 ton ha-1) futhi kumile e-Ethiopia nakwezinye izindawo ezinkulu ezitshala i-sesame e-sub-Saharan Africa ngenxa yobuningi bezingqinamba zokukhiqiza. Isivuno esiphansi se-sesame sibangelwa wukuntuleka kwezinhlobo ezikhiqiza kakhulu futhi eziguquguqukayo, ezinokuqhekeka okuncane kwekhepsuli; ukucindezeleka kwe-biotic kanye ne-abiotic; ukuntuleka kobuchwepheshe besimanje bokukhiqiza izitshalo nengqalasizinda ethuthuke kahle. I-Sesame isalokhu iyisitshalo esingacwaningiwe futhi esisetshenziswa kancane e-Ethiopia naphezu kokubaluleka kwayo kwezomnotho ekuhwebeni kwasekhaya, kwesifunda kanye nakwamanye amazwe. Kunesidingo sohlelo oluzinikele lokuthuthukisa izakhi zofuzo ze-sesame ukuze kuthuthukiswe futhi kusetshenziswe izinhlobo ezintsha ezithuthukisiwe ezinezimpawu ezikhethwa abalimi nezimakethe. Ngakho-ke, izinhloso eziqondile zalolu cwaningo kwakuyilezi: i) ukubhala amathuba nezingqinamba zokukhiqiza i-sesame kanye nezinhlobo nezici ezikhethwa abalimi nezimakethe empumalanga naseningizimu-ntshonalanga ye-Ethiopia njengomhlahlandlela wokuzalanisa; ii) ukunquma izingxenye ezihlukene, ukutholakala komqondo obanzi (h2b) kanye nokuhlotshaniswa kwezici ezihlobene nembewu nesivuno sikawoyela ku-germplasm ye-sesame yase-Ethiopia ukuze zizale ngempumelelo; iii) ukunquma izinga lokuhlukahluka kofuzo phakathi kwamaqoqo e-sesame germplasm ayikhulu (100) ahlukahlukene ase-Ethiopia kusetshenziswa izimpawu ze-phenotypic kanye nezimpawu eziphindaphindayo ezilandelanayo, phecelezi, i-Simple Sequence Repeat (SSR) nokukhetha izinhlobo zofuzo ezihlukile nezihlukile zokuzalanisa kanye iv) ukunquma ukuhlukahluka kofuzo kanye nobudlelwano phakathi kwamaqoqo e-sesame germplasm yase-Ethiopia kusetshenziswa okuqukethwe kukawoyela wembewu kanye nokuqanjwa kwe-esidi enamafutha kanye nezimpawu zokuxilonga ze-SSR bese ukhetha imigqa yabazali eyingqayizivele nethembisayo yokuzalanisa. Kwenziwa imisebenzi yocwaningo eyahlukene kodwa ehambisanayo ukuze kuzuzwe izinjongo. Ucwaningo lokuqala lwenziwa kusetshenziswa i-participatory rural appraisal (PRA) ebandakanya abalimi abayikhulu namashumi aysithupha (160) ezifundeni ezimbili ezikhethiwe ezitshala i-sesame kanye nezifunda ezine e-Ethiopia. Ingxenye enkulu yabalimi abaphendulile (56.0%) babike ukuthi balima i-sesame besebenzisa izimbewu zezinhlobo ezingaziwa ezivame ukutholakala emkhakheni wembewu ongekho emthethweni. Izithiyo ezibaluleke kakhulu ekukhiqizweni kwe-sesame ezindaweni zocwaningo kwaba ukuntula ukufinyelela kwembewu ethuthukisiwe (okubikwe ngabangu- 83.0% abaphendulile), isivuno esiphansi sezinhlobo ezikhona (73.8%), izifo (69.4%), kanye nentengo ephansi yemakethe (68.8%). Lezi zingqinamba zidalwe ukushoda kohlelo oluzinikele lokuzalanisa, umkhakha wembewu osemthethweni, izinsiza eziqinile zokwandisa, kanye nengqalasizinda ethuthuke kahle ngaphambi nangemuva kokuvuna. Okubaluleke kakhulu izici ezikhethwa yizimakethe ze-sesame zihlanganisa imbewu yohlobo lwangempela, umbala wembewu emhlophe, nokuqukethwe kwamafutha embewu ephezulu. Intengo enengqondo yemakethe, ukumelana nezifo zezitshalo, ukubekezelela isomiso, ukumelana nezinambuzane zezitshalo, isivuno esiphezulu sembewu, isisindo sembewu eyinkulungwane, uwoyela ophakeme, umbala wembewu emhlophe, ukuvuthwa ngaphambi kwesikhathi, kanye nezimfanelo ezinhle zikawoyela njengephunga nokunambitha kwaba izici ezibalulekile ezikhethwa ngumlimi ngokulandelana kokubaluleka. Ngakho-ke, lezi zici kufanele zihlanganiswe ezinhlelweni zamanje nezesikhathi esizayo zokuzalanisa ama-sesame. Ucwaningo lwesibili luhlole i-germplasm ye-sesame eyikhulu (100) ngaphansi kwezimo zensimu ezindaweni ezimbili kusetshenziswa idizayini ye-lattice engu-(10 x 10) enezimpinda ezimbili. Okutholakele kuveze inani eliphakeme le-genotypic coefficient ye-variation kanye namanani e-h2b yenani lamagatsha ayisisekelo, (i-NPB), inombolo yamagatsha esibili, phecelezi, number of secondary branches (NSB), isisindo sembewu eyinkulungwane, (i-TSW), isivuno sembewu ngehektha ngalinye, (i-SYH) kanye nesivuno samafutha ngehektha ngalinye, (i-OYH), ephakamisa ukuthi izinzuzo eziphezulu zofuzo zingatholakala ngokukhethwa. Imiphumela eqondile ephakeme ye-OYH kanye nenani lembewu nge-capsule ngayinye (NSPC) zarekhodwa ezithinta i-SYH, kuyilapho i-SYH, inani lamaphilisi ngesitshalo ngasinye (NCPP) kanye ne-TSW ibe nomthelela oqondile ophezulu ku-OYH. I-Genotypes u-Hirhir Kebabo Hairless-9, i-Setit-3, i-Orofalc ACC-2, i-Hirhir Humera Sel-6, i-Setit-1 kanye ne-ACC-NS-007(2) bakhethelwe ukuqhubeka nokuzalaniswa ngokusekelwe emvuzweni yabo ephezulu yembewu, okuqukethwe kukawoyela namafutha. Engxenyeni yesithathu yocwaningo, okufakiwe okuyinkulungwane (1000) kwe-sesame kwahlolwa ezindaweni ezimbili e-Ethiopia ukuze kutholwe izici ze-agro-morphological kanye nokuqukethwe kwamafutha embewu kusetshenziswa idizayini ye-lattice engumashumi aphindwe kashumi (10 × 10) enezimpinda ezimbili. Futhi, ukuhlolwa kohlobo lwe-genotype kwenziwa iphrofayili kusetshenziswa omaka be-SSR be-polymorphic abangamashumi amabili nesikhombisa (27) e-Oil Crops Research Institute ye-Chinese Academy of Agricultural Sciences. Ukuhlaziywa kokuhluka kuveze okubalulekile (p ≤ 0.05) ukungena ngokusebenzelana kwemvelo ngobude besitshalo, ubude be-internode, inombolo yamagatsha esibili, nesivuno sokusanhlamvu. Ama-Genotypes afana no-Hirhir Kebabo Hairless-9, i-Setit-3, i-Orofalc ACC-2, i-Hirhir Humera Sel-6, i-ABX = 2-01-2, kanye ne-Setit-1 erekhodiwe isivuno sokusanhlamvu esingu->0.73 ton ha−1. Isivuno sokusanhlamvu sasinezivumelwano ezinhle nezibalulekile (p <0.01) nesivuno samafutha (r = 0.99), okuwusizo ekukhetheni ngesikhathi esisodwa. Ukuhlukahluka kwezakhi zofuzo okumaphakathi kanye namanani okuqukethwe kolwazi lwe-polymorphic we-0.30 no-0.25 arekhodwa ngokusekelwe ekuhlaziyweni kwe-SSR, ngokulandelanayo. Izinhlobo ze-genotype zahlukaniswa zaba amaqembu amabili namaqembu amane, amakhulu, ahlukene ngokusekelwe ekuhlaziyweni kweqoqo kanye nesakhiwo sabantu, ngokulandelana, ngaleyo ndlela kuvumela ukukhetha nokuwela okulandelayo ukuze kuthuthukiswe imiphakathi yokuzalanisa futhi kuthuthukiswe izimila. Ngokusekelwe ekwehlukeni kwe-phenotypic kanye ne-genomic, lawa ma-genotype alandelayo aphezulu futhi ahambisanayo akhethiwe: u-Hirhir Humera Sel-6, u-Setit-3, u-Hirhir Kebabo Hairless Sel-4, u-Hirhir Nigara 1st Sel-1, u-Humera-1 no-Hirhir Kebabo Early Sel-1 (kusuka ku-cluster II-a), i-Hirhir kebabo hairless-9, i-NN-0029(2), i-NN0068-2 kanye ne-Bawnji Fiyel Kolet, (kusuka ku-cluster II-b). Ama-genotype akhethiwe azosebenza njengabazali bohlelo lokuzalanisa u-sesame e-Ethiopia.
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    Breeding maize (Zea mays L.) for resistance to Striga asiatica and S. hermonthica, and compatibility to Fusarium oxysporum f.sp. strigae in Tanzania.
    (2021) Lobulu, Loatha John.; Shimelis, Hussein.; Laing, Mark Delmege.
    Abstract available in PDF.
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    Genetic, agro-morphological diversity and genome- wide association studies in sweetpotato (ipomoea batatas (L) lam.) accessions from Zimbabwe.
    (2021) Chingwara, Victor.; Sibiya, Julia.; Gasura, Edmore.
    Abstract available in PDF.
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    Breeding groundnut for drought tolerance.
    (2021) Tesfamariam, Abady Seltene.; Shimelis, Hussein.; Janila, Pasupuleti.
    Groundnut (Arachis hypogaea L.) is one of the world’s most important grain legumes for its quality edible oil and higher protein content. It is the major cash crop in the semiarid tropics where production is mainly under rain-fed condition. Recurrent drought is the major cause of low yields of groundnut in sub-Saharan Africa (SSA). Farmers in SSA grow unimproved groundnut varieties which are vulnerable to drought stress and insect pests and disease attack. Therefore, there is need to develop drought tolerant, locally adapted and high yielding groundnut varieties for sustainable production of the crop. Breeding groundnut for drought tolerance requires inexpensive, reproducible and high throughput screening systems. Understanding the agromorphological, physiological and molecular bases of drought tolerance aid in the development and release of new varieties with drought tolerance. Therefore, the objectives of this study were: (1) to assess farmers’ perceived production constraints, variety choice, and preferred traits of groundnut in eastern Ethiopia to guide future groundnut variety development and release, (2) to determine drought tolerance, kernel and fodder yield and quality amongst diverse groundnut genotypes for direct production or breeding, (3) to assess the genetic diversity and population structure among 100 groundnut genotypes using agronomic traits and high density single nucleotide polymorphism (SNP) markers, (4) to determine the combining ability effects of eight selected drought tolerant groundnut parental lines and their F2 families under drought-stressed (DS) and non-stressed (NS) conditions to select best performing parents and families for drought tolerance breeding. In the baseline work, participatory rural appraisal studies were conducted in two major groundnut-producing districts (Babile and Fedis) in eastern Ethiopia. The following data were collected involving 150 participant farmers: demographic descriptors, groundnut farming system, farmers’ knowledge about improved groundnut varieties, constraints to groundnut production, market access, and varietal trait preference. Chi-square and t-test analyses were conducted to determine statistical significance among the parameters across districts. Participant farmers identified drought stress (reported by 90% of respondents), poor soil fertility (88%), poor seed supply systems (67%), pre-harvest diseases (root rot and leaf spot) (59.5%), low yielding varieties (52.5%), low access to extension services (41.5%), low access to credit (21.5%) and limited availability of improved varieties (18.5%) as the major groundnut production constraints. The study identified the following farmer-preferred traits: high shelled yield (reported by 27.67% of respondents), early maturity (16.84%), and tolerance to drought stress (13.67%), market value (11.17%), good grain quality (10%), adaptability to local growing conditions (5.8%), and resistance to diseases (5.17%). Therefore, the aforementioned production constraints and farmer-preferred traits are key drivers that need to be integrated into groundnut breeding and variety release programs in eastern Ethiopia. In the second study, 100 groundnut genotypes were evaluated at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)/India during 2018/19 and 2019/20 under drought-stressed (DS) and non-stressed (NS) conditions using a 10 x 10 alpha lattice design with two replications. Seed and haulm samples collected at physiological maturity from DS and NS experiments to estimate Kernel and haulm quality parameters using near infrared spectroscopy (NIRS). Data were collected on kernel yield (KY), oil content (OC), oil yield (OY), protein content (PC), palmitic acid content (PAC), stearic acid content (SAC), oleic acid content (OAC) and linoleic acid content (LAC), haulm yield (HY) and fodder quality parameters such as the contents of dry matter (DM), ash, nitrogen (NC), neutral detergent fiber (NDFDM), acid detergent fiber (ADFDM), acid detergent lignin (ADLDM), in vitro digestibility (IVOMD) and metabolizable energy (ME). Data were subjected to parametric and non-parametric statistical analyses. Combined analysis of variance revealed significant (P< 0.05) genotype differences for all assessed traits. Genotype × water regime interaction effects were significant for KY, OC, ash content, NC, NDFDM and ADLDM. Kernel yield positively and significantly (P<0.05) correlated with oil yield (r = 0.99), LAC (r = 0.13), ash (r = 0.32), NDFDM (r = 0.54) under DS condition. Haulm yield was positively and significantly (P<0.05) correlated with OC (r = 0.24), NDFDM (r = 0.19), ADFDM (r = 0.18) and ADLDM (r = 0.17) under DS condition. Cluster analysis grouped the test genotypes into 12 distinct genetic groups. The study identified genotypes, ICGV 10178, ICGV 01260, ICGV 06175 and ICGV 10379 with high kernel and haulm yields, and CGV 181017, ICGV 01491, ICGV 15019, ICGV 181026, ICGV 16005 and ICGV 181063, with high oleic acid content. Furthermore, genotypes, ICGV 7222, ICGV 10143, ICGV 6040, ICGV 03042, ICGV 06175, ICGV 01260, ICGV 99241, ICGV 96266, ICGV 171027 and ICGV 01491, were selected with relatively better drought tolerance. The selected genotypes are recommended for further breeding and variety release under drought stress environments. In the third study, 99 of the test genotypes were profiled with 16, 363 SNP markers. The following phenotypic data collected during the second study were used for complementing the SNP data: days to 50% flowering (DF), SPAD chlorophyll meter reading (SCMR), Plant height (PH), number of primary branches (PB), specific leaf area (SLA), leaf relative water content (LRWC), total biomass (TBM), pod yield (PY), harvest index (HI), hundred seed weight (HSW), shelling percentage (SHP) and kernel yield per plant (KY) and days to maturity (DM). Analysis of variance, Pearson’s correlation coefficient, principal component and stress tolerance index were calculated. Pod yield per plant (PY), seed yield per plant (SY) and harvest index (HI) were significantly (p < 0.05) affected by genotype × environment interaction effects. Genotypes, ICGV 07222, ICGV 06040, ICGV 01260, ICGV 15083, ICGV 10143, ICGV 03042, ICGV 06039, ICGV 14001, ICGV 11380 and ICGV 13200, exhibited higher pod yield under both drought-stressed and nonstressed conditions. Pod yield exhibited significant (p < 0.05) correlation with SY, HI and total biomass (TBM) under both test conditions. Based on the principal component analysis, PY, SY, HSW, SHP and HI contributed maximum variability for yield under the two water regimes. Hence, selection of these traits could be successful for screening of groundnut genotypes under droughtstressed and non-stressed conditions. Model-based population structure analysis grouped the studied genotypes into three sub-populations, whilst cluster analysis resolved the collections into five clusters based on pedigree, selection history, and market type. Cluster III and Cluster V consisted of the Spanish bunch types, late leaf spot (Phaeoisariopsis personata) and rust (Puccinia arachidis) resistant, and drought-tolerant genotypes. Analysis of molecular variance revealed that 98% of the total genetic variation was attributed to among individuals, while 2% of the total variance was due to variation among the subspecies. The genetic distance between the Spanish bunch and Virginia bunch types ranged from 0.11 to 0.52. Genotypes, ICGV 13189, ICGV 95111, ICGV 14421, and ICGV 171007, were selected for further breeding based on their wide genetic divergence. Data presented in this study will guide groundnut cultivar development emphasizing economic traits and adaptation to water-limited agro-ecologies including in Ethiopia. The fourth study examined the combining ability effects of eight selected drought tolerant groundnut parental lines and their F2 populations under drought-stressed (DS) and non-stressed (NS) conditions under glasshouse and field conditions at ICRISAT in 2020 rainy season. Data were collected on days to 50% flowering (DF), number of primary branches (PB), plant height (PH) (cm), SPAD chlorophyll meter reading (SCMR), specific leaf area (SLA) (cm2/g), pod yield (PY) (g plant- 1), shelling percentage (SHP) (%), kernel yield (KY) (g plant-1 ), total biomass (TBM) (g plant-1) and harvest index (HI) (%). ICGV 10178 was the best combiner genotype to increase SCMR, PY, SHP, KY, TBM and HI and, reduce SLA. The general combining ability (GCA) effects of parents were significant (P<0.05) for all assessed traits under all testing conditions except for PB under DS and NS conditions in the glasshouse. The specific combining ability (SCA) effects of progenies were significant (P<0.05) for all assessed traits except for PH across all testing environments and PB under field condition. Genotype ICGV 10178 was the best general combiner with positive contribution to SCMR, PY, SHP, KY, TBM and HI and reduced SLA. Crosses, ICGV 10178 X ICGV 11369, ICGV 10373 x ICGV 15083, ICGV 98412 x ICGV 15094 and ICGV 10178 X ICGV 98412, were the best specific combiners for enhanced pod yield and drought tolerance. Higher GCA: SCA rations were recoded for PY, KY and TBM across all the testing environments suggesting the predominant role of additive genes conditioning the inheritance of these traits. Therefore, the above new families are recommended for genetic advancement through single seed descent selection method to develop improved pure line groundnut varieties with high pod yield and drought tolerance.
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    Breeding for common bacterial blight resistance in common bean (Phaseolus vulgaris L.) in Ethiopia.
    (2021) Hurisa, Kidane Tumsa.; Shimelis, Hussein.; Laing, Mark Delmege.; Mukankusi, Clare.
    Abstract available in PDF.
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    Genetic improvement of pigeonpea [Cajanus cajan (L.) millspaugh] for yield, earliness and resistance to Fusarium wilt (Fusarium udum Butler) in Malawi.
    (2020) Yohane, Esnart Nyirenda.; Shimelis, Hussein.; Laing, Mark Delmege.; Changaya, Albert Gideon.
    Pigeonpea [Cajanus cajan (L.) Millspaugh, 2n=2x=22] is a one of the important food legumes in Sub-Saharan Africa and Asia. Malawi is a major pigeonpea grower in Africa with production of 403,519 tonnes produced in 248,400 hactares. Pigeonpea is good source of protein and cash income to millions of farmers. Pigeonpea crop residues form excellent animal feed. It serves in atmospheric nitrogen fixation and biomass allocation in the soil. Despite Malawi being the highest pigeonpea producer, grain yield of pigeonpea is low (< 700 kg ha-1) compared with the potential yield of the crop (2000 kg ha-1). The yield gap is due to various production constraints, including Fusarium wilt disease, insect pests, and lack of early maturing and high yielding varieties that are photoperiod insensitive. Breeding and deployment of high yielding, early maturing, and Fusarium wilt resistant cultivars have the potential to enhance pigeonpea production and productivity. The overall objective of this study was to contribute to food security in Malawi through breeding high yielding and farmer-preferred pigeonpea varieties. The specific objectives were: (1) to determine the production constraints affecting pigeonpea, and to identify farmer-preferred traits in Malawi to guide future breeding of pigeonpea; (2) to determine the diversity among pigeonpea germplasm collections using agro-morphological traits to enable selection of genetically distinct lines for breeding; (3) to determine the genetic diversity among the tested pigeonpea germplasm, using single nucleotide polymorphism (SNP) markers to select genetically distinct lines for breeding; (4) to determine the combining ability effects and gene action controlling agro-morphological traits and resistance to Fusarium wilt; and to select the best parents and families from the test population for further breeding. In the first study, a participatory rural appraisal study was conducted in four major pigeonpea-growing districts in southern Malawi (Chiradzulu, Mulanje, Thyolo and Zomba), using a semi-structured questionnaire, transect walks and focus group discussions (FGDs). The results revealed that a landrace pigeonpea variety, ‘Mthawajuni’, was preferred by famers due to its positive attributes such as good taste, early to medium maturity, short cooking time and tolerant to pod borer (Helicoverpa armigera Hubner). Pigeonpea trait preference was dependent on gender, with female respondents preferring rapid cooking, early maturity, long storage and good pest resistance, whereas men focussed on high yields, large seed size, cream seed colour and disease resistance. The study identified the pod borer (H. armigera), Fusarium wilt disease (Fusarium udum Butler), low yields of the existing varieties, drought, and unreliable market prices as the leading challenges affecting pigeonpea production in southern Malawi. A second part of the study focused on phenotypic and genetic diversity and yield stability analyses among pigeonpea accessions in selected target production environments, as a basis to select complementary and unique genotypes for breeding. Eighty-one pigeonpea genotypes were evaluated in six environments in Malawi using a 9 × 9 alpha-lattice design with two replications. Significant genotype variation were recorded for qualitative traits including flower colour, flower streak pattern, pod colour, seed coat colour pattern, seed coat main colour, seed shape and seed eye colour. All evaluated quantitative traits initially were significantly affected by genotype × environment interaction effects except the number of seeds per pod. Genotypes MWPLR 14, ICEAP 01170, ICEAP 871091 and ICEAP 01285 were identified as early maturing varieties, maturing in 125 to 137 days. The genotypes Kachangu, MWPLR 16, TZA 5582, No. 40 and MWPLR 14 had the highest number of pods per plant (NPP) and highest grain yields (GYD). Grain yield was positively and significantly correlated with days to flowering (DTF) (r=0.23, p<0.01), NPP (r=0.35, p<0.01) and hundred seed weight (HSWT) (r=0.50, p<0.01), suggesting the usefulness of these traits for selection to enhance grain yield improvement when assessing pigeonpea populations. Using principal component analysis, three principal components (PCs) accounted for 57.7% of the total variation. The most important traits that reliably discriminated between the test genotypes were DTF, days to maturity (DTM), number of primary (NPB) and secondary branches (NSB), HSWT and GYD. Genotype, environment and genotype × environment interaction accounted for 16.4, 33.5 and 49.6% to the total variation for quantitative traits, respectively. The test environments were delineated into three mega-environments, based on site and seasonal variability. MWPLR 14 (G51), MWPLR 24 (G26) and ICEAP 01155 (G27) were the most stable genotypes for yield across environments, while MWPLR 14, TZA 5582 and MWPLR 4 were the highest yielding genotypes across environments. To broaden the genetic base of the pigeonpea for selection, divergent genotypes such as MWPRL 14, TZA 5582, MWPLR 4, MWPLR 16, Sauma and Kachangu are recommended as parents for targeted crosses. The fourth part of the study examined genetic relationships among 81 genotypyes using 4122 single nucleotide polymorphism (SNP) markers. The SNP markers also confirmed the genetic diversity among the genotypes. The mean gene diversity and the polymorphic information content (PIC) were 0.14 and 0.11, suggesting moderate genetic differentiation among the genotypes. The low genetic diversity and PIC could hinder genetic gains in future pigeonpea breeding programs using this population. The genotypes were delineated into three groups based on population structure and the joint analysis of the phenotypic and genotypic data. The analysis of molecular variance (AMOVA) revealed that differences among clusters accounted for only 2.7% of the variation, while within-cluster variation among individuals accounted for 97.3% of the variation. This suggested that unique breeding populations could be created by identifying and selecting divergent individuals as parental lines. There is a need to create new genetic variation or introgress genes from close relatives to increase the genetic base of pigeonpea since the available genetic variability may not meet the demand for improved cultivars. The phenotypic diversity assessment using morphological attributes grouped the genotypes into three distinct clusters. The mean gene diversity and polymorphic information content were 0.14 and 0.11, respectively, suggesting moderate genetic differentiation among the genotypes. The genotypes were delineated into three heterotic groups based on population structure and the joint analysis of the phenotypic and genotypic data, suggesting the possibility of creating unique breeding populations through targeted crosses of parents from divergent heterotic groups. In a third study, the best and most diverse genotypes from the diversity studies with early maturity, Fusarium wilt (FW) resistance from previous studies and farmer-preferred traits were selected for crosses. Finally, the ten selected parental lines were crossed using a factorial mating design and 25 progenies were successfully developed. The parents and progenies were field evaluated at two locations; 1) Chitedze Agricultural Research Station and 2) Makoka Agricultural Research Station in Malawi. The trial design was 7 × 5 alpha lattice design with two replications. The test genotypes were evaluated for FW resistance through a root dip inoculation technique. There was significant genetic variation among parental lines and families for days to 50% flowering (DTF), days to 75% maturity (DTM), plant height (PH), 100 seed weight (HSWT), FW resistance, and grain yield (GYD). Parental lines, ICEAP 87105, and ICEAP 01285 had desirable general combining ability (GCA) (-32.90 and -14.16 respectively) for days to 75% maturity (DTM), parental lines, MWPLR 16, Sauma and Mwaiwathualimi had desirable GCA (319.11, 168.8 and 46.45 respectively) for grain yield (GYD) and parental lines, TZA 5582, ICEAP 00554, Mwayiwathualimi and Sauma had desirable GCA effects (-3.16, -0.54, -0.24 and 0.17 respectively) for FW resistance. Hybrids such as TZA 5582 × MWPLR 22, TZA 5582 × MWPLR 14, and Mwayiwathualimi × MWPLR 22 had desirable specific combining ability (SCA) effects for DTM (-1.22 -1.51 and -0.91 respectively), GYD (80.93, 42.67 and 79.55 respectively) and FW resistance (-1.10, -0.15, and -1.66 respectively). The study further revealed that additive gene effects were important in inheritance of DTF, DTM and PH traits and non-additive gene effects were important in inheritance of GYD, 100 seed weight (HSWT) and FW resistance. This suggest that both pedigree and recurrent selection are important to achieve pigeonpea improvement. Overall, this study determined the present pigeonpea production constraints and farmer-preferred traits in Malawi. Further, significant genetic variations were detected among a diverse set of pigeonpea germplasm for breeding early maturing/short-duration, high yielding and FW resistant varieties. The study developed new breeding populations based on selected complementary parents for variety development and release in Malawi.
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    Breeding for resistance to rice yellow mottle virus and improved yield in rice (oryza sativa L.) in Tanzania.
    (2020) Suvi, William Titus.; Shimelis, Hussein.; Laing, Mark Delmege.
    Rice [Oryza sativa (L.), 2n = 2x = 24] is the second most important staple food crop after wheat (Triticum aestivum L.) serving more than half of the world’s population. In Tanzania, rice is the second most important cereal crop after maize (Zea mays L.). However, rice production and productivity in the country is hindered by several factors. One of the leading biotic constraints is the rice yellow mottle virus (RYMV) disease which is devastating the existing rice varieties, and causes severe yield losses of 20 to 100 % under field conditions. Both landraces and introduced varieties that are grown by farmers succumb to RYMV. Several control strategies have been recommended to reduce RYMV infection: however, the development and deployment of RYMV resistant varieties is the most effective, economical and environmentally friendly approach for subsistence farmers. Breeding for resistance to RYMV and improved yields are the main goals for rice breeders aiming to develop and release improved rice cultivars that meet the preferences of the farmers and their markets. Therefore, the objectives of this study were to: (i) assess farmers’ perceptions, production constraints and variety preferences of rice in Tanzania to guide breeding; (ii) determine variation among Tanzanian rice germplasm collections based on agronomic traits and resistance to RYMV to select unique parents for breeding; (iii) assess the genetic diversity and population structure of rice genotypes using simple sequence repeat (SSR) markers to complement phenotypic profile and select parents; and (iv) determine the combining ability and gene action for resistance to RYMV disease and for key agronomic traits in rice, and thereby to develop new populations of parental germplasm for future breeding. A participatory rural appraisal study was conducted involving 180 participants, using a structured questionnaire and focused group discussions with 90 farmers in the Mvomero, Kilombero and Kyela districts of Tanzania. The results indicated that rice was the most important food and cash crop, followed by maize, cassava (Mannihot esculenta Crantz), sweetpotato (Ipomoea batatas [L..] Lam.), sugarcane (Saccharum officinarum L.), pigeonpea (Cajanus cajan L.), cowpea (Vigna unguiculata [L.] Walp.), sesame (Sesamum indicum L.), common bean (Phaseolus vulgaris L.), cocoa (Theobroma cacao L.), banana (Musa acuminate L.), groundnut (Arachis hypogaea L.), and oil palm (Elaeis guineensis Jacq.). The majority of the respondents (67.2%) used farm saved seed from the previous rice harvest. The major constraints limiting rice production and productivity in all studied areas were diseases, insect pests, frequent droughts, the non-availability and high cost of fertilizers, a limited number of improved cultivars, poor soil fertility and bird damage. The farmers preferred rice varieties with high yield, disease resistance, drought tolerance, high market value, early maturity, attractive aroma, and local adaptation. A systematic rice-breeding program aimed at improving RYMV resistance and incorporating farmers’ preferred traits should be designed and implemented as a means to increase the productivity and adoption of new cultivars by the farmers across the rice-growing areas of Tanzania. Fifty-four rice genotypes were field evaluated at two important rice production sites (Ifakara and Mkindo), which are recognized as RYMV hotspots in Tanzania, using a 6 × 9 alpha lattice design with two replications. There were significant (p<0.05) genotypic variations for agronomic traits and RYMV susceptibility in the tested germplasm. Seven genotypes with moderate to high RYMV resistance identified, namely Salama M-57, SSD1, IRAT 256, Salama M-55, Mwangaza, Lunyuki, and Salama M-19 were identified as new sources of resistance genes. Positive and significant correlations were detected between grain yield and number of panicles per plant (NPP), panicle length (PL), number of grains per panicle (NGP), percentage-filled grains (PFG), and thousand-grain weight (TGW), which are useful traits for simultaneous selection for rice yield improvement. A principal component analysis resulted in five principal components accounting for 79.88% of the total variation present in the assessed germplasm collection. Traits that contributed most to the total genotypic variability included NPP, number of tillers per plant (NT), PL, grain yield (GY), and days to 50% flowering (DFL). Genotypes, Rangimbili, Gigante, and SARO have complementary agronomic traits and RYMV resistance, and can be recommended for further evaluation, genetic analysis and breeding. The genetic relationship and divergence of the 54 rice selected genotypes mentioned above were examined using 14 polymorphic simple sequence repeats (SSR) markers to select unique parents for breeding. Data analysis was based on marker and population genetic parameters. The mean polymorphic information content (PIC) was 0.61, suggesting a high level of polymorphism for the selected SSR markers among the rice accessions. The population structure revealed a narrow genetic base, with only two major sub-populations. Analysis of molecular variance revealed that only 30% of the variation was attributed to population differences, while 47% and 23% were due to variation among individuals within populations and within individual variation, respectively. The genetic distance and identity among genotypes varied from 0.083 to 1.834 and 0.159 to 0.921, respectively. A dendrogram grouped the genotypes into three clusters with wide variation. The selected genetic resources, namely IR56, Mwanza, Salama M-55, Sindano nyeupe, SARO, Gigante, Lunyuki, Rangimbili, IRAT 256, Zambia and Salama M-19, will be useful resources for rice breeding in Tanzania and other African countries because they are genetically diverse. The final study involved combining ability analysis of the above selected genotypes and derived families to assess gene action conditioning RYMV resistance and agronomic traits. Ten parental lines and their 45 F2 progenies were field evaluated at three selected locations using a 5 × 11 alpha lattice design with two replications. The genotype × site interaction effects were significant (p<0.05) for the NT, NPP, NGP, percentage of filled grains (PFG), TGW, rice yellow mottle virus disease (RYMVD) resistance and GY. The variance due to the general combining ability (GCA) and the specific combining ability (SCA) effects were both significant for all assessed traits, indicating that both additive and non-additive gene actions were involved in governing trait inheritance. The high GCA to SCA ratios calculated for all the studied traits indicate that additive genetic effect was predominant. Parental lines, Mwangaza, Lunyuki, Salama M-57, Salama M-19, IRAT 256 and Salama M-55, which had negative GCA effects for RYMVD, and families such as SARO × Salama M-55, IRAT 245 × Rangimbili, Rangimbili × Gigante and Rangimbili × Mwangaza, which had negative SCA effects for RYMVD were selected for RYMV resistance breeding. The crosses such as Rangimbili × Gigante, Gigante × Salama M-19 and Rangimbili × Salama M-55 were selected due to their desirable SCA effects for GY. The predominance of additive gene effects for agronomic traits and RYMVD resistance in the present breeding populations suggest that rice improvement could be achieved through gene introgression using a recurrent selection method. Overall, the present study resulted in selection of agronomically superior and RYMV resistant breeding parents and new rice families for further evaluation and variety release in Tanzania.
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    Breeding wheat (triticum aestivum L.) for drought tolerance, improved yield and biomass allocation through chemical mutagenesis.
    (2020) Olaolorun, Boluwatife Modupeoluwa.; Shimelis, Hussein.
    Abstract available in PDF.
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    Breeding maize for resistance to the fall armyworm (Spodoptera Frugiperda J.E. Smith), improved yield and yield-related traits.
    (2020) Kasoma, Chapwa.; Shimelis, Hussein.; Laing, Mark Delmege.
    Maize production and productivity in sub-Sub-Saharan Africa (SSA), including Zambia, has been severely threatened by the recent arrival of the fall armyworm (FAW) (Spodoptera frugiperda J.E. Smith). Several strategies have been proposed to control FAW. Integrated pest management (IPM), emphasizing host-plant resistance, has been identified as the most sustainable approach. However, validated and locally-adapted FAW-resistant maize cultivars have not yet been developed and deployed in sub-Saharan Africa. The aim of this research was to develop FAW resistant, farmer-preferred and locally adapted maize varieties. The specific objectives of this study were: (1) to identify farmers' maize production constraints and preferred traits, and to assess farmers' perceptions of the impact of FAW on maize production and productivity in Zambia; (2) to screen a diverse population of maize genotypes for FAW resistance, yield, and yield-related traits by phenotyping and genotyping, to select the most promising genotypes for crossing; (3) to optimise the methods for laboratory rearing of FAW, and to conduct artificial screening of promising maize genotypes under controlled conditions and artificial FAW infestation; (4) to determine the level of genetic diversity for agronomic and FAW-related traits among the test population of maize genotypes using SNP markers complemented by phenotypic information to identify suitable parents for developing FAW-resistant breeding populations; and (5) to determine the nature of gene action conditioning FAW resistance, yield, and yield-related traits through combining ability analysis, and to identify the most promising crosses for continued evaluation in FAW resistance breeding. In the first study, participatory rural appraisal (PRA) surveys were conducted in two FAW affected districts in Zambia in 2017 and 2018, using semi-structured questionnaires, preference ranking and focus group discussions. The high cost of fertilizers, the limited availability of agricultural lands, insect pests, and drought stress were reported by 73, 55, 38 and 36.6% of the respondents, respectively, as the main production constraints. There were significant differences (X2 = 12.415; p = 0.002) in the severity of FAW infestation between the two surveyed districts in 2017. Farmer-preferred traits of maize were insect pest resistance, early maturity, drought tolerance and market price of the grain. FAW resistance, drought tolerance and grain yield performance are the key drivers for maize variety development and deployment in Zambia. In the second study, two sets of diverse maize germplasm were assessed for FAW resistance and desirable yield-related traits in a FAW-affected area in Zambia. Set I and Set II, containing 60 and 253 maize genotypes, respectively, were selected, based on their agronomic potential and adaptability. Highly significant differences (P < 0.001) were detected among the test genotypes for FAW leaf damage (FLD), FAW cob damage (FCD) and agronomic traits. The lowest levels of FLD and FCD were 8.87% and 5.36%, recorded for genotypes CML304-B and CML442, respectively. Five principal components (PCs) accounted for ≥80% of the total variation associated with reduced anthesis-silking interval (ASI), plant height, FLD and FCD, desirable ear aspect and grain yield. Genotypes such as Pool 16 and ZM 7114 from Set I, and CZL1310c, CML444-B, CZL15220 and TL1512847 from Set II had low mean FCD and FLD values, suggesting higher levels of FAW resistance. Grain yield was negatively correlated with mean FLD (r = 0.18, p <0.05), and FCD (r = 0.15, p < 0.05). Promising maize genotypes, including CZL1310c, CML444-B, CZL15220, TL1512847 and CML491, were selected for their low mean FLD and FCD, earliness to flowering and high grain yield potential. These genotypes should be useful in developing tropical and sub-tropical maize breeding populations with partial FAW resistance and yield gains. The third study optimised laboratory rearing and artificial inoculation of FAW onto maize plants under controlled conditions. Field-collected FAW egg masses and larvae were used to mass-produce fresh colonies of the larvae and to evaluate 63 maize genotypes for FAW resistance. The study enabled an understanding of the salient features of FAW growth and development under local environments to implement integrated FAW management strategies. Test genotypes had differential reactions to FAW infestation under controlled conditions. Several genotypes, including CML545-B, CZL1310c, VL050120, CZL16095, EBL169550, ZM4236, MM501 and Pool 16, exhibited considerable FAW resistance at the seedling and leaf-whorl growth stages, and were selected for resistance breeding. The study established a standardised laboratory and screen house-based protocol for mass rearing and artificial infestation of FAW to screen maize genotypes for resistance breeding programs in Zambia or other sub-Saharan Africa countries. The fourth study determined the genetic diversity of 59 maize genotypes of diverse genetic backgrounds with variable resistance to FAW, using phenotypic traits and SNP-based DArT markers. The test genotypes were profiled using agro-morphological traits, FAW damage parameters, and Diversity Array Technology Sequencing-derived single nucleotide polymorphism (SNP) markers. Significant (p < 0.001) differences were observed among the genotypes for 13 phenotypic traits, with their phenotypic coefficient of variation ranging from 2.19 to 51.79%. Notable phenotypic variation was observed for ear position, grain yield, and FAW-induced leaf and cob damage. The mean gene diversity and polymorphic information content were 0.29 and 0.23, respectively, reflecting a moderate level of genetic variation among the test genotypes when assessed using SNP markers. Analysis of molecular variance revealed greater genetic variance within a population than between populations. Population structure and cluster analysis grouped the test genotypes into two main clusters. Three genetically divergent, open pollinated varieties were selected for their favourable agronomic performance and FAW resistance for population improvement or hybrid breeding: Pool 16, ZM 4236 and ZM 7114. The genetic diversity detected within and among the tested populations will facilitate the breeding of maize varieties incorporating farmer-preferred agronomic traits and FAW resistance in Zambia and related agro-ecologies. The fifth study investigated the combining ability effects and inheritance of FAW resistance and agronomic traits in maize genotypes selected for breeding. A line × tester mating design was used and 60 experimental hybrids were generated and field-evaluated in three FAW hotspot locations in Zambia. Both the general and specific combining ability effects were significant (p<0.05) for the assessed traits. Non-additive genetic effects were more important for the inheritance of grain yield and FAW-inflicted leaf and cob damage, suggesting that heterosis breeding would be the best strategy for yield gains. The narrow sense heritability (h2) estimates for agronomic and FAW-related traits ranged from 0.14 to 0.47 and 0.37 to 0.49, respectively. The experimental hybrids CML346/EBL16469, ZM4236/CML545-B, CML346/CZL1310c, CML334/EBL173782, CML545-B/EBL169550 were among those selected with favourable specific combining ability estimates for greater grain yield, reduced days-to-50% anthesis, days-to-50% silking, FAW leaf and cob damage resistance, respectively. The selected experimental hybrids are recommended for further evaluation and breeding. Overall, the study developed and optimized the techniques for the artificial rearing and infestation of FAW on maize under controlled conditions. Promising inbred lines and new FAW resistant experimental maize hybrids were developed involving landrace varieties and donor parents sourced from the International Maize and Wheat Improvement Center (CIMMYT). This study contributes to the development of FAW resistant maize varieties in Zambia and SSA.
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    Genetic improvement of cowpea [vigna unguiculata (L.) walp.] for grain yield and yield component components in Zambia.
    (2020) Nkhoma, Nelia.; Laing, Mark Delmege.; Shimelis, Hussein.
    Abstract available in pdf.