Masters Degrees (Plant Breeding)

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Assessment of groundnut (Arachis hypogaea L.) for genetic diversity using agro-morphological traits and SSR markers.
(2019) Chipeta, Olivia.; Sibiya, Julia.
Groundnut (Arachis hypogaea L.) offers one of the cheapest sources of proteins and economic empowerment to smallholder farmers in Africa, contributing significantly to world production and trade. Thus, improved groundnut seed with high quality attributes is needed. Therefore, pre-breeding activities involving agro-morphological attributes such as yield, disease tolerance/resistance, plant architecture among others are important in order to develop superior genotypes with the needed quality attributes. This study focused on assessing the performance and level of phenotypic variability and genetic diversity of groundnut genotypes using agronomic and morphological attributes, and simple sequence repeat (SSR) markers. Twenty-seven groundnut genotypes collected from International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Malawi) and Chitedze Agricultural Research Station (Malawi) showed highly significant differences in relation to number of branches, days to flowering, leaf color, seed yield and shelling percentage except for aflatoxin content and groundnut rosette disease. Moderate to high broad-sense heritability (0.56-0.71) was observed for number of branches, days to flowering and leafspot disease. The genotypes grouped into three main distinct clusters with those bred for low aflatoxin accumulation falling in the same cluster. Principal component analysis (PCA) had two PCs explaining 57.7% of the total variation with number of branches, flowering and aflatoxin contributing the most to the first PCA. Five genotypes; MP-68, ICGV-94379, ICGV-93305, CDI-1314 and CDI-0009 were identified as high yielding with low aflatoxin concentration hence are recommended for further pre-breeding activities such as increasing yield and resistance to diseases and aflatoxin. Using 20 SSR markers, 39 groundnut genotypes of diverse origin maintained at Agricultural Research Council – Grain Crops Institute in South Africa (ARC-GCI were assessed for genetic diversity. Results showed polymorphic information content (PIC) averaging 0.71, indicating the markers were very informative. A wide genotypic diversity with highest dissimilarity index of 6.4 between genotype pair RG562 and RG288, and smallest dissimilarity index of 0.9 between RG512 and RG562 was observed. Allelic diversity analysis showed high diversity among genotypes from southern Africa and southern America as indicated by the Shannon information index, mean number of observed alleles (Na) and mean number of effective alleles (Ne) which were relatively higher than in other groups. Analysis of molecular variation (AMOVA) results indicated that variation between and within individuals was more significant than between populations. Discrimination of the genotypes was not dependant on the geographical origin as genotypes belonging to different origins clustered in the same groups. Thus, genotypes with wide diversity can be used in breeding programmes as parents.
Assessment of maize germplasm lines for genetic diversity, cultivar superiority and combining ability.
(2012) Khoza, Suzan.; Derera, John.; Laing, Mark Delmege.
Maize (Zea mays L.) is an important crop in the world; however, its yield is compromised by new production challenges leading to poor yield in sub-Saharan Africa. This calls for a need to enhance maize adaptation to changing climate and challenging environments. The new maize varieties should be richly endowed with high frequency of genes that confer high yield under stress and non-stress conditions. Currently, such maize is not available, prompting research into development of new germplasm lines for use in developing new hybrids. The objective of the study was to determine i) the level of genetic diversity using SSR molecular markers and phenotypic data in a set of 60 maize inbreds from the breeding program, ii) genotype by environment interaction in maize hybrids, iii) cultivar superiority, iv) combining ability effects, v) the relationship between yield and secondary traits and vi) the relevant genetic parameters that underpin genetic gains in a breeding program. To study genetic diversity present in the germplasm, phenotypic data and 30 SSR markers were used to estimate the genetic distance between the inbreds. The results indicated that inbred lines which were put in the same cluster were related by pedigree and origin. To assess the level of genotype by environment interaction (GXE) and cultivar superiority of the new germplasm lines, hybrids were planted in five environments with two replications. Data were analysed using the REML and AMMI tools in GenStat 14th edition. The results revealed significant differences between hybrids and environments for grain yield. However, GXE interaction was also significant indicating possible challenges which can be encountered in selecting new hybrids. To determine combining ability estimates two different testers were used. The REML tool from GENSTAT was used to perform the line X tester analysis. Results indicated that both additive and non-additive gene action were important for grain yield. The direct selection strategy for yield was recommended because heritability of grain yield was high. Overall, results suggested that the information on genetic diversity will assist in defining heterotic groups; which will enable effective and efficient management of the germplasm lines to produce new maize hybrids.
Assessment of sweet sorghum lines for genetic diversity using quantitative traits and SSR markers.
(2016) Chinyama, Sombo.; Sibiya, Julia.; Odindo, Alfred Oduor.
The increase in energy demand, volatile oil prices and climate change has led South Africa to reduce its dependency on fossil fuels and promote biofuels. Sweet sorghum [Sorghum bicolor (L.) Moench] has been considered as one of the promising crops due to its sugar-rich stalk to supplement sugarcane which is the major feedstock for bioethanol. Establishing genotypic variability for biomass yield and sugar-related traits in sweet sorghum is therefore essential for developing superior cultivars. The objectives of the study were: (i) to assess sweet sorghum lines for agronomic performance and genetic diversity using quantitative morphological traits and (ii) to assess sweet sorghum lines for genetic diversity and interrelationships using simple sequence repeat (SSR) markers. Twenty-five sweet sorghum lines collected from International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Kenya) and the African Centre for Crop Improvement (ACCI-South Africa) were evaluated during the 2015/2016 season in KwaZulu-Natal (KZN) province at Ukulinga Research Farm in Pietermaritzburg and Makhathini Research Station in Jozini. Seven agronomic traits; fresh biomass yield, fresh stalk yield, grain yield, plant height, stalk diameter, panicle length and days to 50% flowering, and six quality traits; fibre, dry matter, °brix, °total brix, total fermentable sugars and ethanol were recorded. The sweet sorghum lines revealed highly significant variations for the 13 quantitative characters assessed in this study. The extent of variation was highly influenced by environment and genotype by environment interaction. Genotypes designated as IS 2331, IESV 92008 DL, ICSV 700, AS 244, URJA and SS 27 were identified as suitable genotypes with high plant height, dry matter, fibre, °brix, °total brix, total fermentable sugars and ethanol. The specified genotypes also exhibited medium to late maturity with relatively high fresh biomass and fresh stalk yield. Genotype 91018 LT showed the highest fresh biomass yield, fresh stalk yield, stalk diameter and relatively high grain yield. High levels of trait heritability were observed for fresh stalk yield (98%), stalk diameter (93%), fresh biomass yield (81%), panicle length (76%), fibre (73%) and plant height (66%). Heritability estimates were influenced by the environment and genotype by environment interaction. Principal component analysis resulted in the first three principal components showing 83% of the total variability among the genotypes. Ethanol, total fermentable sugars, °total brix, fresh stalk yield and °brix contributed mainly to PC 1, whereas fresh biomass yield and stalk diameter contributed mainly to PC 2. The dendrogram generated from cluster analysis divided the genotypes into two main clusters and three singletons (ICSB 324, ICSB 654 and ICSV 700). Cluster I comprised 54% of the total germplasm and included only one ACCI genotype (SS 27), while cluster II comprised of 33% of the total variation. The morphological variability analysis of the genotypes was also complimented with the use of molecular markers. The 24 sweet sorghum lines were genotyped with 10 simple sequence repeat (SSR) markers and distance-based method was used to analyze the data. Variation was observed for all the markers with allelic size ranging from 1 to 36 bp. A total of 61 alleles were generated with an average of 6.1 alleles per locus. The polymorphism information content (PIC) values ranged from 0.32 to 0.86 with an overall mean value of 0.62, showing a high discriminating ability of the markers used. The largest genetic distance was observed for AS 244 (GD = 1.9), while IESV 92001 DL and IESV 92008 had the smallest genetic distance (GD = 0.50). The dendrogram generated from cluster analysis using SSR markers classified the 24 sweet sorghum lines into two major clusters. Cluster I comprised of 12.5% of the total genotypes which included URJA, SS 27 and ICSB 654. It was observed that all ACCI genotypes apart from AS 244 were grouped in Cluster I, with URJA and SS 27 being very closely related. Cluster II was observed to be the largest (87.5%) with 21 genotypes, which further formed 3 sub-clusters (A, B and C) and a singleton (AS 244). The results from molecular marker characterization were similar to those obtained using PCA analysis of morphological traits which grouped genotypes into four clusters, with the same type of genotypes in each group. The information obtained in this study coupled with phenotypic characterization can be used by plant breeders to select parents or pure lines that can be used in developing improved cultivars. This will therefore contribute to the production of sweet sorghum and promotion of its use for bioethanol in South Africa.
Breeding investigations for development of specialty green maize hybrids.
(2011) Qwabe, Fikile Nozipho Pricilla.; Derera, John.; Tongoona, Pangirayi.
Green maize (Zea mays L.) provides food security and cash income to rural households in Sub-Saharan Africa (SSA). However, research on green maize varieties is scarcely reported in the literature. Consequently there is no information on suitable genetic materials (germplasm) for green maize production. Additionally there is no data regarding quality attributes of suitable hybrids, which impacts on variety development and management. Breeding investigations were therefore conducted to investigate farmers’ preferences for hybrids and attributes of green maize hybrids in KwaZulu-Natal, in South Africa, and to determine combining ability for green maize traits of experimental inbred lines that were derived from an experimental population. The study also investigated the relationships between green maize traits and some desired agronomic traits; and also sought to identify specific inbred combinations (hybrids) with potential for green maize production. A case study was conducted at Mjindi (MJD) and Ndumo (NDO) Irrigation Schemes in KwaZulu - Natal South Africa, to determine the attributes of the “ideal” hybrid, production constraints, production trends and enterprise viability. Prior to a formal survey some focus group discussions were conducted, then 64 green maize growers were interviewed using a formal questionnaire. The study indicated that the most desired consumer traits were a combination of sweet taste, long shelf life and large ears. The required attributes of the model hybrids were high grain yield potential, high selling ability, flint grain texture, white grain color, medium ear placement, thick and long ears, short maturity period, medium plant height, long shelf life and nonpopping during roasting. This study also showed that the enterprise was viable with average gross margin of about R10,000 per ha which makes it attractive to both small and large-scale commercial farmers with implications for rural development in the second economy. Thus there is a great business potential, but lack of suitable and special hybrids appears to be the major production constraint which should be addressed by research and development. A total of 100 advanced maize inbred lines were crossed in a line x tester mating scheme to generate 200 experimental hybrids. The hybrids with sufficient seed were evaluated for green maize and agronomic traits at three sites in KwaZulu-Natal. Large genotype x environment interaction effects were observed which was reflected by the different ranking of hybrids at each site resulting in selection of different sets of top 15 hybrids with potential for production in each environment. Only a few hybrids exhibited high performance consistently in at least two mega environments. The results showed that hybrids were highly significantly different for the green maize traits such as ear yield, ear length, single ear weight and marketability indices, and also for the agronomic traits. The difference among hybrids for marketing ability indices was attributed to the testers main effects and specific combining ability (SCA) effects. Differences between the general combining ability (GCA) of the lines and testers, and SCA effects were significant for the green maize traits. These findings suggested that the traits are governed by both additive and non-additive gene effects, respectively. Additionally observation of continuous and normal distribution of hybrids for the traits indicated that quantitative minor genes were involved and therefore the base population can be improved by selection for large ears, superior marketability index, and high single ear yield. The observed top performing hybrids were recommended for further testing at many sites. Results confirmed that the current dominant variety is not adapted to summer production conditions in the Mjindi and Ndumo areas which present opportunities for breeding programmes. Future studies should therefore aim to improve both the genetics and production economics of specialty green maize hybrids to further enhance profitability of the enterprise with positive implication for the rural economy in KwaZulu-Natal.
Characterisation of cowpea accessions based on agro-morphological traits, nutritional quality and molecular markers.
(2017) Ringo, Goodluck Douglass.; Sibiya, Julia.; Odindo, Alfred Oduor.
Abstract available in PDF file.
Characterisation of selected bread wheat (Triticum aestivum L.) genotypes for drought tolerance based on SSR markers, morpho-physiological traits and drought indices.
(2018) Mdluli, Sibusiswangaye Yolanda.; Shimelis, Hussein Ali.
Bread wheat (Triticum aestivum L.) and durum wheat (T. turgidum L. var. durum) are staple cereal food crops worldwide. In South Africa, bread wheat is the second most economically important cereal after maize. Drought stress associated with climate change is a major cause of the yield gap in wheat production in South Africa. Drought tolerant wheat cultivars are yet to be developed and released in the country. Wheat improvement for drought tolerance is one of the major breeding goals in South Africa. Integrative pre-breeding techniques involving genotypic and phenotypic characterisation ensure an accurate selection of potential drought tolerant parents for breeding. Therefore, the specific objectives of the current study were: 1) to determine the genetic diversity and population structure of forty-seven diverse bread wheat genotypes introduced from the International Maize and Wheat Improvement Center (CIMMYT) using ten selected polymorphic Simple Sequence Repeat (SSR) markers, 2) to characterise fifteen bread wheat genotypes introduced from CIMMYT using physiological and morphological traits, and 3) to assess drought tolerance amongst fifteen selected bread wheat genotypes using nine drought tolerance indices. Genetic diversity and population structure of 47 CIMMYT derived bread wheat genotypes were examined using 10 SSR molecular markers. All the SSR markers used in the study were highly polymorphic. The highest PIC values were recorded for XGWM 132, WMS 179 and WMS 30 with 0.93, 0.89 and 0.89, respectively. Cluster analysis detected 3 distinct clusters with Clusters A and C consisting of most diverse genotypes. Two distinct heterotic patterns were identified to select unique parents for crosses. Analysis of molecular variance (AMOVA) detected significant genetic diversity among populations, among individuals and within individuals with explained percentage variance of 3%, 37% and 60%, respectively. Genetic diversity and population stratification was mainly due to private alleles detected. Based on detected genetic variability, a total of 15 genotypes were selected and subjected for phenotypic characterisation. The selected genotypes included SYM2016-037, SYM2016-038, SYM2016-029, SYM2016-010 and SYM2016-012 from Cluster A, SYM2016-044, SYM2016-004, SYM2016-016, SYM2016-019, SYM2016-014, SYM2016-008, SYM2016-006 and SYM2016-047 from Cluster B and SYM2016-042 and SYM2016-027 from Cluster C. The above selected 15 bread wheat genotypes were evaluated under field and greenhouse conditions using a randomised complete block design with 3 replications. Drought stress was imposed as follows: 1 week before 50% heading (WBH) and 1 week after 50% heading (WAH). A fully-irrigated water regime (NS, non-stress) was used as a comparative control. Genotypes were evaluated using 2 physiological and 8 morphological traits. Significant differences (P < 0.05) were detected among genotypes and genotype x test environment interaction. Genotype effect was significant for days to flowering, days to maturity, plant height, number of productive tillers, number of spikelets per spike, grain number and 100 grain weight. Genotype x test environment interaction was significant for canopy temperature, days to flowering, days to maturity, plant height, number of spikelets per spike, grain number, 100 seed weight and the yield. Significant correlations were detected between yield and days to flowering, days to maturity, plant height, number of productive tillers, number of spikelets per spike, grain number and 100 seed weight under greenhouse condition. The number of productive tillers per plant and the number of spikelets per spike were positively associated with yield under field evaluation. Principal component analysis revealed PC1 to be consistently associated with yield, 100 seed weight and number of spikelets per spike. Days to flowering and maturing, plant height and canopy temperature were positively associated with either PC2 or PC3 under greenhouse and field conditions. A yield penalty was noted for early flowering and maturing genotypes such as SYM2016-014, SYM2016-027 and SYM2016-029 relative to late flowering and maturing genotypes SYM2016-016, SYM2016-037 and SYM2016-006. Crossing of these complementary lines and continuous selection of progenies is essential to develop early maturing genotypes with stable and high yield potential. In this study, days to flowering and maturity, plant height, canopy temperature and 100 seed weight were favourable traits to screen genotypes for drought tolerance. Screening for drought tolerance under greenhouse condition was more reliable than under field evaluation. The above 15 wheat genotypes were evaluated using 9 drought tolerance indices based on yield data. The drought indices used were drought resistance (DR), mean productivity (MP), harmonic mean of yield (HM), stress susceptibility index (SSI), stress tolerance index (STI), tolerance index (TOL), yield index (YI), yield reduction index (YR) and yield stability index (YSI). Analysis of variance detected significant differences among genotypes (P < 0.001) and genotype by water regime interaction (P < 0.01) affecting yield response. Significant differences were also recorded among genotypes (P < 0.05) for DR, HM, MP, STI, YI and YSI. Consistent mean genotype ranking was recorded for HM, MP, STI, SSI and YI enabling selection of genotypes SYM2016-006, SYM2016-016 and SYM2016-037. PC analysis detected high variation of 82.2% among genotypes, with percentage variation partitioned as follows: 42.64% for PC1, 22.37% for PC2 and 12.18% for PC3. Both PC and bi-plot analyses revealed strong associations between HM, MP, STI, YI and yield under drought stressed and non-stressed conditions. High yielding genotypes such as SYM2016-006, SYM2016-016 and SYM2016-037 scored higher values for HM, MP, STI, YI and yield under drought stressed and non-stressed conditions. DR was associated with early maturing genotypes such as SYM2016-014, SYM2016-029 and SYM2016-38. These genotypes were considered as potential parents for future wheat breeding programmes emphasizing drought tolerance.
Characterisation of sweet sorghum germplasm based on agro-morphological traits, molecular markers and juice related traits.
(2018) Nundwe, McDonald.; Sibiya, Julia.; Shargie, Nemera Geleta.
There is rising interest for alternative energy sources because of the decline in fossil fuel production and concern over environmental pollution. Currently most biofuel is based on maize and sugar cane as raw materials. However, the use of feedstocks has triggered concerns related to food security, while sugar cane has a high-water consumption and high production requirements amongst other drawbacks. A crop which meets several requirements for biofuel (such as high biomass yield and growth rate, perennial growth, low input requirements, adaptation to the marginal areas, and tolerance to multiple stresses) is sweet sorghum. This study, therefore, aimed at characterising sweet sorghum germplasm using agro-morphological traits and molecular markers (single nucleotide polymorphisms (SNP) during the 2016-2017 summer season at two sites (Ukulinga farm and Potchefstroom). Fourteen quantitative traits were evaluated in an alpha lattice (10 x 5) design with three replications. Analysis of variance for the quantitative traits revealed high levels of genetic variability. This implies that morphological traits differed greatly with a significant G x E interaction across the two sites. Most of the accessions yielded high at Ukulinga than Potchefstroom on juice yield and %brix with a mean yield of 9 605 l/ha and 16.3%, respectively. Most of the accessions studied were early to medium maturing, as evidenced by the mean number of days to 50% flowering (74 days). Analysis of principle components showed that the first four principle components (PC) accounted for 79.12% of the total variation and that some quantitative traits were significantly positively correlated. The estimates for phenotypic coefficient of variation (PCV) were higher than those of genetic coefficient of variation (GCV) for all the traits, indicating the influence of the environment on these traits. However, GCV values for days to 50% flowering, plant height, stalk diameter and stalk yield were very close to PCV. This indicated minimal influence of the environment on the phenotypic expression of these traits. The highest broad sense heritability (H2) of 99.2% was recorded for plant height. Juice volume had the highest expected genetic advance, expressed as a percentage of mean (GAM) of 131.2%. Days to 50% flowering were significantly and positively correlated to plant height, stalk diameter, number of leaves, stalk yield, brix, juice volume and bagasse weight, but negatively significantly correlated to panicle length, panicle width, panicle weight and 1000 grain weight. Plant height was significantly positively correlated to stalk diameter, number of leaves per plant, stalk yield, juice volume and fresh bagasse weight. Bagasse weight, brix, stalk diameter, plant height and number of leaves had a highly positive and direct contribution on juice yield. Several traits had a highly positively and indirect contribution on juice yield via these traits which had a direct contribution. This revealed primary and secondary traits with practical relevance to sweet sorghum improvement programme, because they showed direct and indirect effects on juice yield (volume), which ultimately translates to sugar yield for ethanol production. Kompetitive Allele Specific Polymorphism (KASP) genotyping using 137 SNP markers revealed a considerable level of genetic diversity among the sweet sorghum accessions. Three populations were generated from the analysis. The expected heterozygosity (He) values ranged from 0.236 to 0.291 with a mean of 0.266. The mean of effective alleles across populations was of 1.438. The percentage of polymorphic loci ranged from 80.29% to 91.24% with a mean of 86.86%. Dissimilarity indices ranged from 0.000 to 0.583 with a mean of 0.296. The highest dissimilarity index was observed between SA 2193 and SA 2014, which implied a considerable amount of genetic diversity. Accessions were clustered into three main groups based on dissimilarity indices. The study identified SA 4490, SA 2400, SA 4495, SA 2193 and SA 4479 as superior accessions in juice yield. These accessions should be used as parents in sweet sorghum improvement programme.
Combining ability analysis of maize inbred lines and genotype x environment interaction of hybrids for grain yield and maize streak virus resistance.
(2018) Juma, Sheila Natividade.; Derera, John.; Sibiya, Julia.
Abstract available in PDF file.
Combining ability and genotype-by-environment Interaction analyses among early-to-medium maturing maize hybrids under drought and non-drought environments.
(2021) Dlamini, Mandisa Noxolo.; Sibiya, Julia.; Musvosvi, Cousin.
Developing high yielding early to medium maturing maize hybrids for Southern Africa represents an effective way to contribute to improving crop productivity in the face of climate change and unpredictable weather patterns. The objectives of this study were: (i) to determine combining ability and gene action among germplasm lines for grain yield (GY) and other traits under drought and non-drought conditions using the line x tester mating design (ii) to explore genotype-by-environment interaction (GEI) patterns of the developed hybrids and identify broadly and specifically adapted entries, with the intention of developing early to medium maturing hybrids for South Africa and the sub region. Twenty-three white maize inbred lines sourced from the International Maize and Wheat Improvement Center (CIMMYT) were crossed in a line x tester mating design involving 13 lines (females) and 10 testers (males), resulting in 122 successful single-cross (SC) hybrids. The SC hybrids and six commercial hybrid checks were evaluated in a 13x10 alpha lattice design, replicated twice under drought and non-drought conditions across three sites viz: Cedara Research Station, Ukulinga Research Farm and Makhathini Research Station over three seasons, (2018-2019 summer growing season, the 2019 offseason, and 2019-2020 summer growing season). Data for grain yield and its related traits was collected. Genetic analysis of the line x tester data followed a fixed effects model. The parents differed in general combining ability (GCA) effects for GY and other traits under drought and non-drought conditions. Likewise, the crosses varied in specific combining ability (SCA) effects for GY and other traits under the drought and non-drought regimes. Line CZL1380 and tester CML539 were good general combiners for GY under drought. Lines CML568, CKDHL0378, CKDHL0467, CML672, and CZL1380 and testers CML312 and CML547 had good GCA effect across non-drought regime. Two crosses, CML540 x CML547 and CKDHL0467 x CML312 had high SCA values for GY under drought and non-drought regimes. The additive type of gene action was predominant for days to anthesis (AD), days to silking (SD), anthesis-silking interval (ASI) plant height (PH), ear position (EPO), ears per plant (EPP), ear aspect (EA), grain texture (GTX), grain moisture (GMH), kernel row number (KRN), and shelling percentage (SHL) under drought, and for AD, SD, ear height (EH), EPO, EPP, EA, GTX, GMH, ear length (EL), kernels per ear row (KER), ear weight (EW), and hundred kernel weight (HKW) across non-drought conditions. Non-additive gene action prevailed for EH, EL, ear diameter (ED), KER, EW, HKW, and GY under drought and for ASI, PH, ED, KRN, SHL, and GY across non-drought conditions. The identified hybrids could be targeted for release as cultivars, and the types of gene action are practically relevant for improvement of early to medium maturing maize germplasm for Southern Africa. Grain yield data from the five environments was analysed to explore genotype by environment (GEI) among the developed hybrids and checks. Analysis of variance across all the environments showed huge environmental, genotypic and GEI effects, with the environment contributing the largest proportion of the variation followed by genotype and lastly GEI. The additive main and multiplicative interaction effects (AMMI) and the genotype and genotype-by-environment interaction (GGE) methods were employed on selected 62 entries to visualize the GEI patterns. The AMMI revealed that two interaction principal component axes (IPCA1 and IPCA2) were significant, and these contributed 50.32 % and 20.84%, respectively, to the total GEI variation. The AMMI1 revealed that hybrid MAK1-122 x CML545 was specifically adapted to drought conditions whereas hybrids CKDHL0467 x CML312 and CZL1380 x CML547 were broadly adapted. The identified two high yielding and broadly adapted experimental hybrids were superior to the best check WE3127 across all environments. Hybrids CML569 x CML566 and CKDHL0467 x CML547 were specifically adapted to irrigated conditions. The GGE-biplots had two principal components, PC1 and PC2, which together explained 69.87% of variation due to genotype and GEI. The GGE-biplots showed similar GEI patterns as AMMI, with the same hybrids identified as broadly and specifically adapted. The identified hybrids could be assessed further in multi-environmental and multiple stress trials to confirm their suitability under high and low input production systems in South Africa and the sub-region.
Combining ability, genetic gains and path coefficient analyses of maize hybrids developed from maize streak virus and downey mildew resistant recombinant inbred lines.
(2015) Mathew, Isack.; Derera, John.
Farmers in SSA continue to obtain low yields (less than two tonnes per hectare) despite the high potential yield (about 14 tonnes per hectare) that can be achieved. The development of improved and high yielding hybrids can help to reduce this gap significantly. Characterisation of maize inbred lines is crucial for developing high yielding maize hybrids. A line x tester analysis involving 38 crosses generated by crossing 19 maize inbred lines with two tropical testers was conducted for different agronomic traits. The maize inbred lines used in this study were sampled from a bi-parental inbred population developed by a shuttle breeding program at University of KwaZulu Natal. The objectives of the study were to estimate combining ability of inbred lines and hybrids, to evaluate the performance of the hybrids in agronomic traits and grain yield, to calculate breeding gains achieved through selection and to deduce the relationship between secondary traits and grain yield. In total 50 hybrids, including control hybrids were evaluated in the trial. The hybrids were planted in the summer season of 2014/15 under rainfed conditions at three sites, Cedara, Dundee and Ukulinga in five metre row plots and replicated twice in 5X10 alpha lattice design under recommended agronomic practices for maize. Data was collected using a CIMMYT protocol and subjected to statistical analyses using ANOVA and REML packages in GENSTAT 14th edition and PATHSAS macros in SAS 9.3 computer software. The results showed varying performances between the lines, crosses and control hybrids at the different sites. Inbred lines DMSR-8, DMSR-13, DMSR-30 and DMSR-35-5 were shown to have good combining ability while DMSR-21 and DMSR-73 showed positive specific combining ability. Selection across sites improved grain yield by 9.32% over the population mean and by 10.22% and 12.73% at Cedara and Dundee, respectively over commercial hybrids. Ranking by mean yield identified hybrids 15XH16, 15XH20 and 15XH28 at Cedara, Dundee and Ukulinga respectively, as the highest yielding hybrids for that particular environment. GGE biplot and AMMI analyses revealed that hybrids 15XH10, 15XH13, 15XH20, 15XH25, 15XH28, 15XH34 and 15XH39 were the most stable hybrids. Secondary traits were found to be associated with grain yield potential of hybrids. Ear prolificacy had the most important relationship with grain yield and was recommended for selection in grain yield improvement programs.
Effect of insect pollinator species deployment and interactions with parental inbred lines in hybrid carrot seed production.
(2021) Skosana, Tebogo Lucky.; Sibiya, Julia.; Musvosvi, Cousin.
Insect pollinator species are highly valued for their contribution towards cross-pollination in many vegetable crops for food and seed production. Honeybees (Apis mellifera) are a significant main pollinator not only in entomophilous crop, but for many other plants in their natural habitats. Moreover, attempts to increase seed production through the introduction of an alternative pollinator species (such as Calliphorides flies) throughout the world have encouraged growers and breeders to think more precisely about the management of these pollinators for the future. However, several constraints, including climate, have resulted in low success of pollinators, thereby failing to meet pollination demand for hybrid carrot seed production, both nationally and internationally. The goal of this study was to identify alternative non-bee insect species that can be used as agents of pollination in commercial hybrid carrot seed production. The research experiment was conducted in Matjiesrivier farm (33o23'31.86" S and 22o05'14.91" E) that is situated under the Oudtshoorn district municipality, which is a Cango valley of Western Cape Province. Carrot parents were three cytoplasmic male sterile (CMS) lines, which were pollinated by two pollen donor-male inbred lines. Two insect species, honeybees (Apis mellifera) and Calliphorid flies (Chrysomya chloropyga), were used as agents of pollination. The experiment was arranged in a 2x2x3 factorial with two replications. The weight of umbels, seed weight and germination percentage data were collected to achieve research study objectives. Statistical analysis for all data was done using SAS (SAS Institute Inc, 2018) and R (R Core Team, 2019) statistical computation software. The data were subjected to analysis of variance (ANOVA) for individual umbel level (order) harvests. The TUKEY post hoc test was done at a 5% level of probability to compare the treatments. From the results, flies were comparably effective as honeybees during pollination, while analysis of variance for quantitative traits (germination percentage, seed weight, and umbels weight) was highly significant implying that the traits differed among the advanced lines and the deployment of the two species during pollination. The trait variability was influenced by the umbel stages of different CMS lines and their interaction with pollinator by male fertile and male sterile lines. This information will be useful in a breeding program that focuses on hybrid seed production in carrots and a combination of the two insect pollinators’ deployments to improve cross breeding for future management would be essential
Efficacy of mon 89034 bt trait in conferring fall armyworm resistance in high yielding three-way and single-cross maize hybrids.
(2020) Chingombe, Pretty Nyaradzo.; Derera, John.; Yobo, Kwasi Sackey.
Maize production, especially in tropical sub-Saharan Africa, is hampered by the fall armyworm (FAW) posing a serious threat to food security and livelihoods. Many methods of control including pesticide use have been tried against FAW but without sustainable success. The main objective of this study was to investigate whether or not the Bt trait (MON89034) could be successfully integrated in high yielding tropical hybrids and confer effective resistance to FAW when deployed in three-way and single cross hybrids. The study was conducted under natural FAW hotspot conditions and under field conditions representative of farmer’s situation. Conventional non-genetically modified (non-GM) tropical single cross hybrids and inbred lines were crossed to four WEMA Bt lines. The resultant three-way and single cross hybrids were evaluated at three sites, in South Africa. The results indicated adequate discrimination of hybrids according to FAW resistance and grain yield, under both FAW infestation and at two other sites with limited FAW pressure. The experimental Bt hybrids displayed high yields exceeding 5 t/ha and higher FAW resistance, which was comparable to standard genetically modified (GM) control hybrids. In sharp contrast, the conventional non-GM control hybrids recorded yield as low as 0 t/ha, under FAW infestation. They were highly susceptible to FAW which was indicated by high damage scores. Therefore, the event MON89034 was effective in conferring FAW resistance in both three-way and single cross hybrids. Although the environment main effects were highly significant (P<0.001) for grain yield, the three-way cross hybrids were relatively stable and showed non-significant (P>0.05) genotype x environment interaction (GxE) effects. In sharp contrast, GxE effects were highly significant (P<0.001) for grain yield of single cross hybrids, indicating that they were less stable than their three-way counterparts. New Bt hybrids with high cultivar superiority index and combining high yield potential and FAW resistance were identified. These included (H3WX3167Bt) (HSX5054Bt), (HSX5368Bt) and (H3WX3194Bt). The three-way experimental hybrid (H3WX3167Bt) had yield advantage of 64% above WEMA GM checks, 33% above local GM hybrid checks and 22% above conventional non-GM checks. The single cross experimental hybrid (HSX5368Bt) exhibited yield advantage of 127% above mean of conventional non-GM checks, 100% above mean of WEMA checks and 99% above mean of local GM checks, under FAW infestation. In addition, secondary traits, such as ear prolificacy and number of ears harvested per plot, which had significant direct and indirect effects for grain yield under FAW infestation were identified for use in construction of a viable selection index. Overall, the study was successful and showed efficacy of the Bt trait (MON89034) in conferring FAW resistance when deployed in tropical high yielding three-way and single cross hybrids. The best performing experimental Bt hybrids with high yield and high FAW resistance, and out-yielded both GM and non-GM standard commercial hybrids, would be advanced in the breeding program that targets the GM market segment in tropical Africa. A survey of the literature has not revealed prior studies on evaluation of FAW resistance in three-way cross hybrids. The trait is deployed predominantly in single cross hybrids, in the GM maize production lead countries, such as Argentina, Brazil, China, South Africa and USA. Therefore, this study formed a significant baseline for revealing useful information on the efficacy of the Bt trait in conferring FAW resistance in three-way cross hybrids which are predominantly deployed to smallholder farmers in tropical Africa.
Evaluation and identification of single-cross maize hybrids for use in tester development.
(2018) Makavu, Barnaba Lameck.; Mashingaidze, Kingstone.; Sibiya, Julia.
Development of testers from new inbred lines that are high yielding and high discriminating abilities in diverse environments, and in stress conditions is very important in maize breeding in southern and eastern Africa. Genetic gain decreases when new lines are combined with old testers. It is, therefore, important to develop new testers that perform better in harsh environmental conditions to replace the old single-cross testers; CML 312 x CML 442 (heterotic group A) and CML 444 x CML 395 (heterotic group B). These are currently dominating the maize breeding programmes at the Agricultural Research Council (ARC) and most of the National Agricultural Research stations (NARS) in eastern and southern Africa. The objectives of this study were therefore; i) to identify elite single-cross hybrids suitable for further evaluation as potential testers in development of three-way cross hybrids, ii) to determine the correlations between grain yield and secondary traits in single-cross maize hybrids, and iii) to estimate phenotypic and genetic variance components, heritability and genetic advances for yield and its related components in single-cross maize hybrids. The trials were established under three different environments which are: random drought (RD), optimum environment (OPT) and low nitrogen (Low N) at ARC Potchefstroom and Cedara using alpha lattice 0, 1 design (32 x 5). The single-cross hybrids used in this study were obtained from CIMMYT Zimbabwe and they belong to two different heterotic groups as follows;, heterotic group A with 160 entries among which 155 were experimental single-cross hybrids and five were check entries and heterotic group B with 160 entries among which 157 were experimental single-cross hybrids and three were hybrid checks. High significant differences (P< 0.01) among single-cross hybrids were observed on days to 50% anthesis (AD), grain yield (GY), ear height (EH), and ears per plant (EPP) in heterotic group B under optimum environment. Hybrid 139 had a mean yield of 8.65 t/ha, which was higher than the average grain yield of 6.22 t/ha. Days to 50% anthesis (AD), anthesis-silk interval (ASI), plant height (PH), and EH varied significantly (p<0.01) among single-cross hybrids in the low nitrogen environment. Hybrid 65 had a mean yield of 4.04 t/ha, which was higher than the average yield of 2.29 t/ha. Days to 50% anthesis were slightly higher in low nitrogen environment than in optimal environment. Hybrid 92 had a mean yield of 7.53 t/ha, which was higher than the average yield of 4.77 t/ha in random drought environment. As in heterotic group B, significant variations were observed in heterotic group A, in random drought and optimum environments. Grain yields of 9.44 t/ha and 6.42 t/ha for maize hybrids 134 and 52 were higher than average mean yields of 6.75 t/ha and 3.43 t/ha from optimum and random drought environments, respectively. Hybrids with higher trait values than the average may be advanced for further use in breeding in their respective environments. Maize single-cross hybrids 1, 23, 127, 15, 122, 8, 134, 109, 34, and 31 from heterotic group A and 69, 81, 65, 97, 92, 40, 117, 58, 101, and 44 from heterotic group B were selected for further use in breeding. The hybrids had consistently higher mean yields across the environments. Significant, positive and negative correlations were observed among secondary traits in all environments. Yield (t/ha) was positively correlated with cob length (CBL), EH, field weight (FW), grain weight (GW) and shelling percentage (SP). It was however, negatively correlated with days to 50% silking (SD) and days to 50% anthesis (AD). A breeding programme aimed at improving CBL, EH, FW, GW and SP and reducing traits SD and AD may indirectly result in improvement of maize yields in random and optimum environments. High genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were observed for ASI, yield t/ha, PH and ear height therefore, and selection can be done. Improvement of maize yield based on AD and ASI selection would be successful due to their high broad sense heritability estimates. The genetic advance observed in this study were high and therefore some trait values can be increased in the next generation through selection.
Evaluation of advanced sorghum lines for use as possible parents in breeding for bio-ethanol production.
(2017) Mashombo, Awadhi Abdulrahmani.; Sibiya, Julia.; Shargie, Nemera Geleta.
Abstract available in PDF file.
Evaluation of early maturing maize (zea mays L.) hybrids for multiple-stress tolerance.
(2018) Ndlala, Lucia Zinzi.; Sibiya, Julia.; Mashingaidze, Kingstone.
Maize (Zea mays L.) is the most important cereal in Africa, but a number of constraints including biotic, abiotic and socio-economic factors affect its production. The abiotic factors such as drought, low nitrogen (N) and heat contribute to the low grain yield production, which creates a challenge that needs to be addressed by researchers. Thus, development and use of early maturing maize hybrids could help in stabilizing maize production. Early maturing maize hybrids help in reducing the growing period to escape some of the abiotic stresses that contains variability for high yield potential and adaptive traits. This study, therefore, was aimed at breeding and identifying early maturing maize hybrids cultivars that are tolerant to drought and low N stresses. Fifty early maturing maize hybrids including six commercial checks were evaluated under stress and non-stress environments during the 2016/17 maize growing season in South Africa. The objectives were (i) to estimate variance components, correlation and path coefficients among grain yield and secondary traits in early maturing maize hybrids across stress and non-stress environments and (ii) to evaluate genotype by environment interaction effects and stability for grain yield performance in early maturing maize hybrids across stress and non-stress environments. To estimate the variance components, correlation and path coefficients among grain yield and secondary traits in early maturing maize hybrids across stress and non-stress environments, quantitative traits data including grain yield and its secondary components were recorded. Statistical analyses revealed that the effect of genotype, environment and genotype by environment interaction were significant (P<0.01) for all the traits. Hybrids CZH16084, CZH16064 and CZH16095 under managed drought, low N and optimum environments, respectively, were identified as the outstanding genotypes for grain yield and recommended for further testing, release and registration. High magnitude of phenotypic and genotypic coefficient of variation as well as high heritability were recorded for each single environment for anthesis days, silking days, ear height and plant height, suggesting that those traits interacted with the environment. Grain yield was positively correlated with anthesis days and ear height, field weight, grain moisture at Potchefstroom while at Lutzville and Cedara had negative correlation with those traits, suggesting that the genotypes differed significantly for most of the phenotypic traits. Path coefficient analyses revealed that anthesis days and anthesis-silking interval had positive direct effects while silking days, plant height and ear per plant had a negative direct effect on grain yield in all the environments. These traits are recommended for effective selection to the improvement of maize grain yield. To evaluate genotype by environment interaction effects and stability for grain yield performance in early maturing maize hybrids across stress and non-stress environments, data collected from all environments which were Lutzville (managed drought), Potchefstroom (optimum), Cedara (optimum) and Cedara (low nitrogen) during the 2016/17 summer planting season, were subjected to ANOVA and GGE biplot analyses. Analysis of variance for individual environments showed that the genotype mean squares were significant at P<0.01. The ANOVA across environments showed that the genotype, environment and genotype by environment interaction mean squares were significant at P<0.01 for grain yield. From the GGE biplot analysis, the two principal components (PC1 and PC2) contributed 64.8% of the total variability due to genotypes plus genotype by environment interaction, with PC1 and PC2 accounting for 35.97% and 28.83%, respectively. The use of GGE biplot analyses provided a clear basis for determining the stability and performance of the 50 early maize hybrids and ranked them according to order. The best performing genotypes were G13 (CZH15448), G46 (CZH15574), G15 (local check 2), G33 (CZH16094), G7 (CZH16083), G20 (CZH16090) and G4 (CZH16089). The following hybrids were adapted to specific environments as follows: G26 (CZH16070), G34 (CZH16074), G9 (CZH15499) and G18(CZH16071) at Cedara (optimum) conditions; G46 (CZH15574), G40 (CZH16069) and G12 (CZH16080) excluding the checks G23 (local check 1) and G14 (SC301) at Potchefstroom (optimum); G22 (CZH16093), G6 (CZH15575), G49 (CZH16068) and G17 (CZH15600) excluding the check G15 (local check 2) at Cedara (low N) and G33 (CZH16094), G37 (CZH15184), G41 (CZH16082), G28 (CZH16076) and G8 (CZH16065) at Lutzville (managed drought). The GGE biplot analysis also identified nine stable and high yielding genotypes, which included G6 (CZH15575), G46 (CZH15574), G22 (CZH16093), G49 (CZH16068), G12 (CZH16080), G17 (CZH15600), G28 (CZH16076), G47 (CZH15452), and G8 (CZH16065). These genotypes will contribute to high maize yields and stable grain production in specific and across environments and are therefore, recommended for further testing and release.
Evaluation of maize hybrids for low-nitrogen stress tolerance, yield stability and genetic purity.
(2019) Josia, Chimwemwe Chabulika.; Sibiya, Julia.; Mashingaidze, Kingstone.
Nitrogen stress is among the major abiotic constraints that impede maize production in Africa. Therefore, development of maize varieties that are tolerant to low N stress conditions and stable across environments is needed. Assessment of genetic purity of inbred lines and their F1 hybrids is among the quality control measures in hybrid breeding, seed production, variety release as well as intellectual property protection (IP). The objectives of this research were, therefore: a) to assess the grain yield performance, genetic parameter estimates, correlations and conduct path coefficient analysis for grain yield and related traits under low N and optimum conditions, b) to assess the magnitude of genotype by environmental interaction (GEI) and hybrid yield stability under low N and optimum conditions and c) to assess the genetic purity of maize parental lines and their F1 hybrids. To achieve these objectives, 170 single cross maize hybrids were evaluated across low N and optimum environments at three locations in South Africa (SA) during 2017/18 summer season viz. Potchefstroom, Vaalharts and Cedara. The experimental setup comprised of five-production conditions across these three locations. The collected data was subjected to analyses using Genstat software 18th edition, SPSS version 25 and SAS version 9.3. For genetic purity analysis, 158 single-cross maize hybrids along with 30 elite parental inbred lines were genotyped using 92 SNPs markers and the molecular data was analysed using GenAlex software. Results revealed that variance due to environment, genotype and GEI were highly significant (P<0.001) for all the traits under low N and optimum conditions. Lower heritability values were observed for grain yield (0.29) compared to secondary traits including days to anthesis, plant height, ear height and anthesis-silking interval, which had heritability estimates of 0.85, 0.43, 0.38 and 0.52, respectively. Higher phenotypic coefficient of variation (PCV) as compared to genotypic coefficient of variation (GCV) were observed under low N and optimum environments, respectively. Under low N, grain yield was positively correlated with field weight, plant height and ear height, but negatively correlated with days to silking, anthesis-silking interval and leaf senescence. Under optimum environment, grain yield was positively correlated with field weight and ears per plant, and negatively correlated with days to anthesis, days to silking, anthesis- silking interval, plant height and ear height. Highest positive direct effect on grain yield was observed for days to silking and field weight under low N, while under optimum, field weight and days to anthesis exhibited the highest direct effects. AMMI and GGE biplot analyses revealed high yielding hybrids in each specific environment and high yielding and stable hybrids across the environments. Five high yielding and stable hybrids across environments; G134 (I-42/CKDHL0295), G12 (CB399/CML442), G24 (CK21/CML216), G33 (CKDHL0089/CML442) and G102 (CML544/I-42) are recommended for further evaluation and release. Using SNP markers, 66.7% of maize parental lines genotyped were considered pure with residual heterozygosity of <5%, while the remaining 33.3% had residual heterozygosity levels of > 5% hence not pure. Cluster analysis effectively discriminated the parental lines into three distinct genetic clusters. Parent-offspring test conducted on 158 hybrids resulted to the elimination of 38% of the hybrids due to genetic contamination of their parental inbred lines. Of the 68 hybrids that passed the parent-offspring test, seven hybrids, including SCHP29, SCHP95, SCHP94, SCHP134, SCHP44, SCHP114 and SCHP126, were selected as potential candidates for further evaluation and possible release in South Africa due to their outstanding yield performance.
Evaluation of rice genotypes for grain yield and resistance to bacterial leaf blight (Xanthomonas oryzae pv.oryzae) disease.
(2018) Tesha, Claudia Andrew.; Sibiya, Julia.; Musvosvi, Cousin.
Rice (Oryza sativa L.) is a staple food crop in many African countries including Tanzania. However, both regional and national rice production have failed to meet demand due to several constraints, among which is the bacterial leaf blight (BLB) disease caused by Xanthomonas oryzae pv. oryzae. Moreover, attempts to increase rice production through the introduction of modern cultivars has motivated farmers to leave local land races for high yielding, but often susceptible varieties. The overall goal of this study was to increase and strengthen rice production in Tanzania through development of high yielding and BLB resistant varieties. The specific objectives were: to i) analyse genotype x environment interaction (GEI) effects for reaction to bacterial leaf blight under natural infection and rice grain yield performance across different environments in Tanzania ;ii) assess the heritability, variability and efficiency of indirect selection using secondary traits for grain yield improvement among rice genotypes; and iii) assess relationship among traits using correlation, path coefficients and genotype-by-trait associations in rice. The study was conducted at three sites namely Katrin, Igurusi and Kyela, all in Tanzania. Thirty rice genotypes, which include two checks, Txd 306 (susceptible check) and IR- 24 (resistant check), were evaluated. The experimental design was a 6 x 5 alpha lattice design with three replications. Data was collected on early vigour, days to early flowering, plant height (cm), panicle length(cm), number of tillers per hill, dead heart, bacterial leaf blight scoring, lodging percent, days to maturity, dry straw weight (kg), spikelets per panicle, grain length (mm), grain width (mm), 1000-grain weight (g), harvest index (%) and yield per plot (kg). Data were analysed using SAS version 9.4 and GenStat 17th edition. ANOVA was used to detect the significance of GEI. The Additive Main Effect and Multiplicative Interaction (AMMI) and the Genotype plus Genotype by Environment Interaction (GGE) biplot models were used for further analysis of GEI and stability. From the results, genotypes NERICA 4 followed by IR-24 were the most resistant to BLB while Supa India was the most susceptible. Dakawa 83 was the most resistant at Katrin while NERICA 4 was the most resistant at Igurusi and Kyela. Genotypes NERICA 2 and LOWLAND NERICA 6 were the most stable across environments for BLB resistance, while IR54 and Txd 306 were the most unstable. Based on the GGE biplot analysis, the three environments fell into two mega environments where as at Kyela, NERICA 4 and IR-24 were identified as the most resistant genotypes while at Katrin Dakawa 83 and NERICA 1 were identified as the most resistant genotypes. Genotype by Environment Interaction effect for grain yield was not significant and as a result, genotype comparison for the same trait was based solely on mean performance across all the environments. The best three genotypes for grain yield were Txd 306, Txd 88 and WITA 10, but in contrast, NERICA 4, Supa India and Mwanza were the worst performers for the same trait. As for broad sense heritability estimates, days to early flowering had the highest estimate of 99.67%, indicating less influence of the environment, while lodging% had 0.00% heritability indicating high influence of the environment. For variability, the phenotypic coefficient of variation (PCV %) values were higher than the genotypic coefficient of variation (GCV %) for all the traits. The highest PCV(%) was for lodging percent (5325.463) followed by number of spikelets per panicles (1005.352)and the lowest was for grain width (1.197) followed by grain length(2.406).The GCV (%) was highest for number of spikelets per panicle (419.902) followed by plant height (97.843) and the lowest was for lodging percent (0.000) followed by grain yield (0.314), genetic advance (GA) was highest for spikelets per panicles (66.79) and lowest for lodging percent (0.000), while for genetic advance as a percentage of mean (GAM %) the highest was for yield per plot (104.13) followed by dry straw weight (92.11) and the lowest was for lodging percent (0.00) followed by panicle length (8.89).Not all the traits under consideration could be used for indirect selection for yield per plot since none of them had a relative selection efficiency equal to or greater than unity. Regarding diversity assessment, cluster analysis based on Euclidian distance indices revealed that Txd 88 and SATO IX were the most similar pair, followed by IR-56 and IR54, which were also similar to each other, and the most divergent genotypes were Txd 306 and Wahiwahi followed by Wahiwahi and Txd 85. Diverse genotypes can be targeted for hybridization since progenies of diverse parents are often more heterotic than those of related parents. The assessment of relationship among traits using correlation and path analysis the traits which were positive and highly significantly correlated to grain yield were harvest index (0.77***) followed by dry straw weight (0.46***), while negative significant correlations were observed for early vigour (-0.22*). Direct effects on grain yield were positive for harvest index (0.80) and dry straw weight (0.51), while indirect effects were highest for days to maturity through harvest index (0.25) followed by number of tillers per hill through harvest index (0.23). For genotype-by-trait associations, genotypes NERICA 1, NERICA 2, NERICA 4, WAB 450-12-12-BL1- and IR-24 were associated with BLB resistance; on the other hand Txd 306, WITA 10, Txd 88, Txd 85, and SATO I were associated with high yield, although Txd 306 was also associated with susceptibility to BLB, whereby WITA 10 was high yield and resistance to bacterial leaf blight. Moreover this study provided information on the presence of genotype by environment interaction in Tanzanian rice growing environment, valuable blight resistance and high yielding genotypes such as WITA 10 and moderate BLB resistance with high yield for genotypes such as Kalalu, Txd (88) and Txd (85), which could be used in rice breeding improvement and conservation efforts of rice.
Evaluation of soybean (Glycine max L. Merr.) lines for grain yield and drought-tolerance.
(2021) Mathonsi, Thubelihle Lungelo.; Sibiya, Julia.; Kondwakwenda, Aleck.
Soybean (Glycine max L. Merr.) is ranked as the fourth-highest commercial agronomic seed crop in South Africa. An increase in animal feed demand has mainly driven the significant growth in demand for soybean oilcake and oil. This demand is also contributed by increasing demand for protein-rich foods, especially among the middle class. However, soybean production has always been variable in different seasons in South Africa mainly due to the occurrence of droughts in some provinces causing the yields to decline. Therefore, enhancing grain yield and drought tolerance would preserve farmers’ profits at large and smallscale farms. The present study was undertaken during 2019 and 2020 summer growing seasons in the field and greenhouse trials to: i) screen 36 soybean genotypes for drought-tolerance using morphological and physiological traits, ii) assess drought-tolerance in soybean genotypes using drought-tolerance indices and iii) estimate the variance components and heritability of yield and yield components of soybean under wellwatered and water-stressed. Thirty-six soybean lines obtained from the International Institute of Tropical Agriculture (IITA) were screened for drought-tolerance in the field and greenhouse under water-stressed and well-watered regimes using morphological, physiological traits and yield-based selection indices. The targeted traits were; plant height (PH), stem diameter (STD), leaf width (LW), leaf length (LL), seed moisture content (SMOI), stomatal conductance (STC), chlorophyll content (CC), 100 seed weight (SW) and biomass Yield (BMS). High genetic variation was observed in grain yield and morpho-physiological traits under both well-watered and water-stressed regimes. Genotype effect was significant for PH, LL, LW, STD, BM, SW and GY. The water regime indicated a significant effect for PH, LL, LW, STD, SMOI and GY. The environment effect was significant for all morphological traits PH, LL, LW, STD, FLW, SMOI, SW and GY. The environment by water regime interaction showed a significant effect for PH, FLW, SMOI, SW. A significant reduction in agronomic traits was observed for G10, G12, G22 and G29, which were the best potential genotypes for improving drought-tolerance. The PH, LL, LW, STD; GY, SMOI, BM and SW could effectively be used for selection in the yield improvement of soybeans under water stress conditions, since they were positively correlated with GY. The Principal components analysis (PCA) and cluster plot analysis approach was very helpful in identifying high-yielding, drought-tolerant genotypes, discriminating and grouping genotypes based on their responses to water stress. The principal components indicated that first dimension (Dim1) was consistently correlated with PH, LL, LW and STD. The SW, CC, FLW, STC, SMOI, BM and GY were either associated with second dimension (Dim2) or third dimension (Dim3). The cluster plot showed that G1, G10, G12, G20, G22, G25 and G29 under WS in the field experiment had high means values and were consistency associated with STD, LL, STC, FLW, SMOI, BM, SW and GY based on principal components and cluster plot, represented as cluster II. Whistle, G5, G7, G10, G12, G13, G14, G17, G21, G22, G23, G27, G29 and G31, showed significantly high mean values and association with PH, STD, LW, LL, STC, CC, BM, SW and GY in the greenhouse environment. The selection for drought-tolerance among 36 soybean lines under well-watered and water-stressed regime was performed using yield based selection indices, including Drought intensity index (DII), Stress susceptibility index (SSI), yield index (YI), Stress tolerance index (STI), Mean relative performance (MRP), GMP-Geometric mean of productivity (GMP), Yield stability index (YSI), Mean productivity(MP), TOL-Stress tolerance (TOL), Harmonic mean (HM) and Relative efficiency index (REI). The ANOVA indicated that the main effects due to the environment, genotype and water regime were significant for GY at the level of significance of (P≤0.05), (P≤0.001) and (P≤0.001). The drought-tolerant indices with significantly positive correlation with the grain yield under well-watered and water-stressed regimes were MRP, GMP, MP, MRP, HM and REI (P<0.001-P<0.05). These indices were comparably effective than SSI, YI, STI, YSI and TOL in selecting and predicting better grain-yielding soybean genotypes under a well-watered and water-stressed regime. Most of the soybean genotypes studied resembled water stress tolerance, including G22, G4, G8, G1, G23, G5, G20, G24, G27, G25, G16, G14, G7, G2, G28, G11, G6, G34, G10, G30, G3, G15, G19, G36, G17, G21, G31, G18, G33, G35, G13, based yield reduction rankings. Among these genotypes, G1, G19, G13, G33, G31 showed high mean performance, tolerance and association with SSI, STI, MRP, GMP, MP, TOL, HM and REI. However, G26, G32, G9, G29, G12 were considered moderately susceptible to water stress and G7, G8, G14, G22, G34 had low mean performance values and low association with indexes. The 36 imported lines from the International Institute of Tropical Agriculture (IITA) were assessed in the field and greenhouse environments, using a 6×6 alpha-lattice design with two replications. Water stress was applied up two weeks after 50% flowering for each genotype and a well-watered regime was used as a control treatment. The genotypes were screened using morphological and physiological traits including; PH, STD, LW, SMOI, STC, CC, SW, BM and GY for estimating variance components and broad-sense heritability. The present study showed the existence of genetic variability among 36 soybean genotypes examined. Hence, one can examine the presence of variability in these soybean lines for crop improvement programs through indirect selection. According to the results, a higher genotypic coefficient was observed for grain yield under both water regimes, consistent with wide-ranging heritability. The PCV was higher than the GCV for all traits across environments and water regimes, thereby suggesting the significance of the environmental expression for all traits. The PCV was higher than the GCV for all traits in all environments and water regimes, suggesting the importance of the environmental effect for all traits. The PCV values ranged from 7.03 to 92.84, while the GCV values ranged from 0.07 to 60.77. GY and BM showed high PCV and GCV values in each environment and under the respective water regimes, which signifies a considerable genotypic variation in these traits. Additionally, the phenotypic expression of these traits would help identify genotypic potential and are efficient further to be used to improve breeding plants. Because of the reduced effects of environmental stress, there was no clear trend in the traits examined for heritability in both environments and water households. Heritability estimates under WW ranged from -0.34 to 55%, while under WS, they ranged from -0.29 to 43%. Overall, most traits had low heritability in both water regimes. Consequently, one should be careful in selecting for droughttolerance using the traits examined.
Evaluation of soybean [Glycine max (L.) Merrill] genotypes for grain yield and associated agronomic traits under low and high phosphorus environments.
(2018) Pedro, Joao António.; Sibiya, Julia.; Chigeza, Godfree.
Phosphorus is an important element for growth, development and seed formation in soybean and other plant species. This element is less available for plants. The capacity of absorbing phosphorus in the soil varies from one genotype to another, so that, the selection of phosphorus use efficient soybean lines is crucial in order to enhance the production. The main objectives of this study were: i) to identify soybean varieties that are tolerant to phosphorus deficiency ii) to determine the agronomic characters that contribute directly and indirectly to the yield improvement by correlation and path coefficient analysis and iii) to determine genotype x environment interaction effects and stability of soybean genotypes in respect to grain yield across low and optimum phosphorous environments. Thirty advanced soybean lines were evaluated in an alpha-lattice design, with two replications during 2016/2017cropping season under low phosphorus (0 kg/ha) and high phosphorus (100 kg/ha) levels in seven environments. Data were collected for fifteen phenotypic traits (both quantitative and qualitative) and analysed using SAS, breeding view (BV) in breeding management system (BMS), and Excel. Correlation and path coefficient analysis were done to determine the traits that contributed directly and indirectly to yield. Results for correlation and path coefficient analysis demonstrated strong and significant associations of yield with yield components. Harvest index was highly significant and positively correlated with grain yield but negatively with plant height, days to maturity and days to flowering. Path analysis revealed that under low P environment, total dry biomass, harvest index, number of pods could be used to screen soybean lines for low P, likewise in high P, harvest index, 100-seed weight, and plant height could be used in selection for high P use efficiency. Plant height, number of pods and nodule weight were identified as the traits that could be used for selection of the lines across all environments. The yield was high under high phosphorus (1551.20 kg/ha) than under low phosphorus environment (1154.30 kg/ha). The best yielding genotypes under high phosphorus were TGx2025-9E, TGx2025-6E and TGx2016-3E. Likewise, for low phosphorus the best genotypes were TGx2025-9E TGx2016-3E and TGx2023-3E. Across the two environments, genotypes TGx2025-9E and TGx2016-4E were the best. The genotypes were clustered into six groups with the maximum dissimilarity index of 0.6. In AMMI analysis, genotype TGx2025-9E, was the most stable and high yielding, suggesting the potential value of the variety as an alternative for soybean production across all environments. GGE biplot resulted in three mega-environments from the seven environments; Kabwe1, Lilongwe1, Lilongwe2 and Lusaka composed mega environment one, Gurue1 and Gurue2 formed mega environment two and Kabwe2 mega environment three. The best performing genotypes in these mega-environments were SCSAFARI and TGx2019-1E (mega-environment 1), TGx2025-9E (mega-environment 2) and TGx2025-6E (mega-environment 3). These findings highlighted the need for increased GxE studies to enhance efficiencies of breeding for broad adaptability in respect to responsiveness to low phosphorus.
Evaluation of the performance of groundnut genotypes and their resistance to groundnut rosette virus.
(2017) Makweti, Lutangu Jethrow.; Gubba, Augustine.; Sibiya, Julia.
The groundnut or peanut is one of the important legume crops of tropical and semi-arid tropical countries, where it provides a major source of edible oil and vegetable protein. The crop is mainly grown by smallholder farmers with little inputs, resulting in low yields of 700 kg/ha compared to Asia and south America which records 3500 kg/ha and 2500 kg/ha respectively. The low yields are due to a number of abiotic and biotic factors with diseases being a major constraint. Amongst the diseases, groundnut rosette disease can cause up to 100% yield loss when infection occurs. The objectives of this study were to; (i) evaluate the ICRISAT elite lines for rosette resistance using artificial inoculation, (ii) determine the effect of genotype by environment interaction of landraces and elite lines and select for stability and high yield, and (iii) determine the genotype by trait interaction for the landraces so as to select potential genotypes for use as parents in the breeding programme. To achieve objective one, glasshouse and field inoculation experiments were conducted using the infector row technique. In the glasshouse, the results revealed that ICGV SM 08503 and ICGV SM 01514 were resistant and showed 0% disease incidence while ICGV SM 01711, ICGV SM 09547, ICGV SM 09537, ICGV SM 08501 and ICGV SM 09545 showed moderate resistance with scores ranging from 1.1 to 1.7. ICGV SM 02724, ICGV SM 10005 and ICGV SM 08560 showed high susceptibility with scores as high as 4.6. However, the susceptible genotypes ICGM SM 10005, ICGV SM 02724 and ICGV SM 08560 showed low incidences of the disease in the field evaluation. At 60 days after sowing (DAS), the incidence ranged from 9.9% to 16.5% while at 80 DAS, it ranged from 18.6% to 23.8%. The highest score for disease incidence at 100 DAS was 27.3% for genotype ICGV SM 08560. The rest of the genotypes had 0% incidence. The yield per hectare ranged from as low as 0.32 ton/ha to as high as 1.03 ton/ha. ICGV SM 10005 recorded the lowest yield while ICGV SM 01711 was the highest yielding genotype with 1.03 ton/ha. For the genotype x environment study, a total of 11 groundnut genotypes from ICRISAT comprising of nine elite lines and two released cultivars as controls were evaluated over ten environments spread across the three agro-ecological zones of Zambia in the 2016/17 season. Additive main effect and multiplicative interaction (AMMI) and genotype and genotype by environment interaction (GGE) biplot models showed that ICGV SM 01711 and ICGV SM 02724 were high yielding recording 2.08 t/ha and 1.99 t/ha, respectively, compared to the average mean of 1.67 t/ha across all environments and showed relative stability. ICGV SM 10005 and ICGV SM 08560, which are Spanish genotypes, yielded 1.67 t/ha and 1.60 t/ha, respectively, compared to Luena (control) which yielded 1.23 ton/ha. ICGV SM 10005 had better relative stability over ICGV SM 08560 and Luena. Genotype x trait analysis, correlation and path coefficient analysis on a total of eight landraces, two pre-released cultivars and five released cultivars showed a strong and highly significant correlation for grain yield with number of pods per plant, yield per plant, shelling percentage and 100-seed weight with r values of 0.86, 0.90, 0.94 and 0.23, respectively, at P<0.001 but 100-seed weight’s correlation was not significant. The path coefficient analysis revealed that yield per plant, shelling percentage, number of pods per plant, 100-seed weight and days to maturity had a positive direct effect on grain yield while days to flowering had negative direct effect on grain yield. Genotype by trait (GT) biplot captured 83.00% of the variation due to genotype by trait interactions. Two land races, Kasele and Chalimbana performed relatively well in relation to MGV 4 and it was recommended that these could be hybridized with genotypes that have complementary features so that beneficial alleles are combined for improvement of the crop, while genotypes ICGV SM 01514, ICGV SM 01711 and Chishango can be used as sources of resistance genes.