Masters Degrees (Plant Breeding)

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Sub-imbibed storage of recalcitrant seeds of four species.
(2007) Eggers, Sharon Kim.; Berjak, Patricia.; Pammenter, Norman William.; Erdey, Deon Philip.
The seeds of Trichilia dregeana, Trichilia emetica, Podocarpus henkelii and Syzygium cuminii display the characteristics typical of recalcitrant seeds. It is the phenomena of ongoing metabolic activity and desiccation sensitivity that render them unsuitable for storage by the conventional methods used for orthodox seeds. Investigations on the storage responses of 'sub-imbibed' (partially dried) and fully hydrated seeds of all four species were carried out to study the effects of partial drying on viability and subsequent storage lifespan; i.e. to assess whether 'sub-imbibed' storage is feasible for these species. The outcome of this investigation was proposed to contribute to the resolution of the argument that storing recalcitrant seeds at lowered water contents might extend their longevity; i.e. storage at a relatively high water content but below the fully hydrated level, might prevent germination but would not be sufficient to be injurious to the seed. Seeds of T. dregeana, T. emetica, P. henkelii and S. cuminii were dried to various target moisture contents (which were determined for each species in the initial drying experiment) and then subjected to storage for 3-22 weeks at 6, 16 and 25°C (in sealed containers). In parallel, seeds of each species were stored at the shedding water content. The seeds were periodically removed for sampling, and assessed for water content, germination, respiration, electrolyte leakage and microscopical features. Storage temperature appeared to affect viability of seeds of T. emetica and T. dregeana which displayed characteristics of chilling sensitivity. Storage at 6°C was detrimental (when compared with seeds stored under the same conditions at 16 and 25°C), but regardless of whether the seeds were undried or partially dried prior to storage. The seeds of P. henkelii did not demonstrate chilling sensitivity, the viability not being compromised at 6°C compared with those seeds stored at 16 and 25°C. Syzygium cuminii seeds were not subject to storage at 6°C because previous work indicated that they would be chilling-sensitive. Storage of 'sub-imbibed' seeds of T. dregeana, T. emetica, P. henkelii and Syzygium cuminii does not to confer any benefit over seeds stored in the fully hydrated state; rather it appears to be deleterious to seed survival during storage. This was apparent from the assessment of viability, electrolyte leakage and respiration. Vigour and viability of the 'sub-imbibed' seeds of all species declined more rapidly than the fully hydrated seeds. The only exception was P. henkelii seeds stored at 25°C, the fully hydrated seeds showed no survival after 11 weeks in storage, while 88% of the 'sub-imbibed' seeds survived this period. These results were, however, attributed to the proliferation of fungi on the fully hydrated seeds at 25°C. Although ultrastructural observations were made only on the T. emetica seeds, it was apparent that the cells from the 'sub-imbibed' seeds (after storage at 16 and 25°C) showed extensive degradation, with the intra-cellular components being largely unrecognisable. The cells from the seeds stored in the fully hydrated condition at 16 and 25°C maintained integrity and appeared metabolically active. In keeping with the suggestion that T. emetica seeds are chilling sensitive, the ultrastructure of the cells from both the 'sub-imbibed' and fully hydrated seeds showed deteriorative changes. All the results of the present study indicated that storage in the 'sub-imbibed' state is deleterious to seed survival. It is apparent that the removal of water, however small a proportion, accelerates seed deterioration during storage. Thus 'sub-imbibed' storage has no practical application for the storage of recalcitrant seeds.
Investigation of growth potential of alternative eucalyptus species for mid and high altitude sites in the summer rainfall region in South Africa.
(2008) Otim, Christopher Komakech.; Laing, Mark Delmege.
A study was undertaken to compare growth potential of three Eucalyptus species of natural origin in South Eastern Australia, with commercially grown species on mid and high altitude temperate sites in the summer rainfall growing zones in South Africa. The three species were Eucalyptus globulus subsp. bicostata (E. bicostata), Eucalyptus cypellocarpa and Eucalyptus nobilis. Nine sites were selected to represent the growing areas of South Africa experiencing cold winter drought with occasional snow falls. Improved, commercially grown pure Eucalyptus species and interspecific hybrid clones were included as controls in the trials to give comparative growth performances on specific sites. Both balanced and unbalanced lattice designs were used to evaluate the growth potential of the unimproved Australian species and the improved commercial controls incorporated into the trials. Volume production and basal area growth were assessed for the three species at all sites. However, only three sub species E.globulus (E. bicostata, E. maidenii and E. globulus) showed varying levels of disease (Mychosphaerella nobilosa) infestation and this was therefore assessed in trials at 12 and 30 months respectively, and correlation analysis was used to study the relationship between the impact of disease infestation and growth performance. It was found that negative phenotypic correlations existed between the levels of infection and tree growth. ie greater infection slower growth. Evaluation of genotype x environment interaction (GXE) revealed that this did not exist in the E. bicostata nor E. nobilis populations, and therefore one population of each species can be developed for all the sites tested. E. cypellocarpa was the only species that showed some GXE interaction implying that separate populations to be developed for different sites. Contrary to what was expected, unimproved Eucalyptus species being investigated performed equally as well as the improved commercial species included as controls, thus providing potential for commercial deployment with selection and breeding.
A quantitative study on growth, basic wood density and pulp yield in a breeding population of Eucalyptus urophylla S.T. Blake, grown in KwaZulu-Natal.
(2008) Van Deventer, Francois.; Laing, Mark Delmege.
The first objective of this study was to evaluate Eucalyptus urophylla S.T. Blake provenances in terms of their growth, basic wood density and pulp yield properties. The second objective was to determine the genetic and phenotypic associations that may exist between growth, basic wood density and pulp yield. Data of 9022 open-pollinated progenies representing 306 families, collected from 17 provenances, were used to evaluate growth. To evaluate basic wood density and pulp yield, as well as the genetic and phenotypic associations between the three traits, data of 300 open-pollinated progenies representing 30 selected families from 11 provenances were used. Narrow-sense heritabilities for all three traits were estimated from data collected in a single E. urophylla provenance/progeny trial planted in northern KwaZulu-Natal. The results showed that significant provenance effects for growth, basic wood density and pulp yield were observed. Heritability was found to be strong for basic wood density (h2 = 0.51) and moderate to weak for volume growth and pulp yield (h2 = 0.17 and h2 = 0.11, respectively). This suggests that big genetic gains can be achieved for basic wood density. Although the heritability estimates for volume growth and pulp yield were weaker, this still allows for tree breeders to make significant genetic gains through accurate selection from this E. urophylla breeding population. Genetic and phenotypic associations between the three traits were estimated from data collected in the same trial. The genetic correlation between volume growth and pulp yield was positive and moderately strong (rA = 0.66). The genetic correlation estimate between volume growth and basic wood density was found to be negative but weak (rA = -0.08). The genetic association between pulp yield and basic wood density was found to be positive but weak (rA = 0.17). Correlation estimates between volume growth and basic wood density, as well as between pulp yield and basic wood density produced standard errors greater than the correlation itself (s.e. = ± 0.32 and ± 0.22, respectively). These high standard errors, coupled with weak genetic correlations, suggest that these correlation estimates are non-significant, but are probably a result of utilizing a small sample size. However, these correlations have a value in making breeding choices, if treated with caution. Key words: Eucalyptus urophylla, provenance, growth, basic wood density, pulp yield, heritability, genetic correlation
The mutagenesis of Sorghum bicolour (L.) Moench towards improved nutrition and agronomic performance.
(2009) Brauteseth, Evan Michael.
In the breeding of grain sorghum (Sorghum bicolour L. Moench) towards improved nutrition and agronomic performance, new methodologies are required to increase genetic diversity and lower the inputs required to track and screen breeding populations. Near-infrared calibration models were developed by partial least squares (PLS) and test-set validation on 364 sorghum samples to predict crude protein and moisture content on whole-grain and milled flour samples. Models using milled flour spectra were more accurately predictive than those from whole grain spectra for all constituents (eg. Protein: R2 = 0.986 on flour vs R2 = 0.962 on whole grain). Discriminant calibrations were established to classify grain colour using partial least squares discriminant analysis (PLS-DA) based upon CIE L*a*b* reference values and visual ranking. Preliminary calibrations were developed for quantities of 18 amino acids, fat and apparent metabolisable energy (AME) on 40 samples using cross-validation, highlighting potential for reliable calibration for these parameters in sorghum. An investigation into the potential of 12C6+ heavy-ion beam mutagenesis of sorghum seed was undertaken by treatment at RIKEN Accelerator Research Facility (Saitama, Japan) and subsequent breeding at Ukulinga research farm and analysis at the Department of Plant Pathology, University of KwaZulu-Natal, Pietermaritzburg, South Africa. Dosage rates of 75, 100 and 150 Gy were compared in seven sorghum varieties to establish optimal dose treatments as determined by germination and survival rates, visible morphological changes and field data over two seasons of field trials. Crude protein variation within the M2 generation was analysed to compare dose rate effects. The need for higher dose rates was indicated by few quantified differences between treatments and control although good correlations between protein deviation and treatment dose rate were elucidated. Differences in varietal response suggest a need to optimize dose rate for specific varieties in future endeavours. In addition, all mutagenized populations were screened for crude protein content using near-infrared spectroscopy (NIRS). Significant differences in protein levels and standard deviations were observed between treated self-pollinated M2 generations and untreated control populations. Individual plants displaying significantly different protein levels were isolated.
Morphological and cytological diversity of some yams (Dioscorea spp.) in Sierra Leone.
(2010) Norman, Prince Emmanuel.; Tongoona, Pangirayi.; Shanahan, Paul Edward.
Yam (Dioscorea spp.) is a major source of income and a food security crop for many households in Sierra Leone. Despite the economic importance of the yam crop its improvement has suffered from the lack of knowledge of existing germplasm and the genetic potential within the yam gene-pool. As a consequence, many species of yam are being lost to changing tastes, industrialization and urbanization. All these lead to habitat destruction. This study assessed the extent of diversity in some yam germplasm from Sierra Leone using morphological and cytological descriptors, and ascertained the interrelationship between these two data sets. To this end, 52 genotypes comprising of forty three D. alata, two D. bulbifera, and seven D. rotundata sampled from the Sierra Leone germplasm were grown in a three replicate, in a randomized complete block design (RCBD) during 2010 planting season at the University of KwaZulu-Natal, Pietermaritzburg, South Africa. Principal component analysis (PCA) of 28 morphological characters indicated that the first 10 principal components (PCs) with eigen-values greater than 0.6 explained 86.61% of the total variation. The PCs that largely contributed to the variability included number of days to shoot emergence, leaf position, leaf shape, leaf size, density of leaf, leaf vein colour; colour of leaf, petiole, petiole wing and stem, shoot growth rate, tuber shape and flesh colour of central cross section of tuber. The two-dimensional plot of the first two PCs grouped the accessions according to their species, but did not separate them into the tuber shape groups of irregular, oblong, oval-oblong, round and cylindrical. Factor analysis (FA) grouped the morphological traits into six factors, which together explained 75% of the total phenotypic variation in the dependence structure. Factor 1 was strongly associated with absence or presence of wings, distance between lobes, leaf apex shape, leaf colour, leaf margin colour, leaf measurement length-2, leaf vein colour of upper surface, number of branches, number of stems, stem colour and tip length of mature leaf; factor 2 with leaf density, leaf measurement length-1, leaf vein colour of lower surface, petiole wing colour, tip colour, wing colour and flesh colour of central cross section of tuber; factor 3 with leaf measurement width-1; factor 4 with leaf measurement width-2; factor 5 with stem colour; and factor 6 with number of days to emergence. The dendrogram of the cluster analysis produced six major groups supporting the PCA and FA groupings. Clusters A, B, C, D, E and F were formed at the dissimilarity distance = 0.90; and they consisted of two, thirty eight, one, seven, two and two genotypes respectively. Genotypes of cluster A belong to D. bulbifera, while genotypes of clusters B, C, E and F belong to D. alata, and genotypes of cluster D belong to D. rotundata. The ploidy levels of the 52 genotypes were determined by flow cytometry. The various ploidy levels obtained included diploid (2x), triploid (3x), tetraploid (4x), pentaploid (5x) and hexaploid (6x). The estimated nuclear DNA content ranged from 1.634 pg for G1 nuclei of diploid Dioscorea alata to 2.118 pg for G1 nuclei of hexaploid Dioscorea rotundata. Genotypes NR 07/045 (4x) and NR 07/040 (5x), which belong to D. bulbifera had nuclear DNA content of 1.905 and 2.017 pg respectively. The nuclear DNA content per genome was higher in diploids compared to polyploids. The variations within the 4x accessions (p<0.005) and among the three species (p<0.037) were significant. Root tips of six genotypes were prepared for chromosome counting using the acetocarmine staining technique. Genotype ER 07/030 had 20 chromosomes, four genotypes including ER 07/036, NR 07/060, NR 07/071 and SR 07/072 had 40 chromosomes, and TDr 95/18544 had 60 chromosomes. The findings agree with the hypothesis that studied germplasm from Sierra Leone were morphologically different expressing inter- and intra-group variability. Duplicate accessions were observed supporting the hypothesis that some genotypes had different names in diverse cultural setting. Flow cytometric measurements and conventional chromosome counting showed the existence of inter- and intra-group diversity in ploidy level and nuclear DNA content. A correlation was established between agro-morphological and cytological traits used in the study. This study contributes to an understanding of yam diversity in Sierra Leone which will facilitate yam genetic resource management, conservation and utilization.
Genetic and environmental factors affecting rooting in Eucalyptus grandis X Eucalyptus longirostrata hybrid cuttings.
(2011) Naidoo, Nuveshen.; Laing, Mark Delmege.
In clonal deployment programmes of plantation species, there is frequently the need to deploy Eucalyptus species and interspecific hybrids as rooted cuttings. However, the rooting ability of a particular species or hybrid is a major, and usually limiting, factor affecting the economics of commercial deployment. There is also significant between-species and between-family variation for this trait. Recently, Eucalyptus longirostrata was crossed with E. grandis in an effort to combine its desirable wood properties, drought tolerance and disease resistance with the latter's vigorous growth. Should progeny with these suitable characteristics be identified, there is the possibility of extending plantations to more marginal areas and increasing the quality and volume from existing plantations. An investigation was undertaken to study the rooting ability of E. grandis x E. longirostrata hybrid cuttings. The plant material was sourced from five families in seedling derived hedges at two nurseries, as well as five families coppiced from an unreplicated progeny trial planted in the midlands of KwaZulu-Natal. Their rooting ability was assessed by determining the percentage of cuttings that developed roots using two different rooting methods. The variation between and within families and clones is presented. The study shows that root strike is under moderate genetic control, with an estimate of broad-sense rooting heritability of 0.197 (S.E. = 0.070). The two nurseries used in this study used different rooting technologies, with cuttings rooted either in media (traditional method) or in air (aeroponically). The aeroponics technology was highly significantly (p<0.0001) superior, in terms of rooting success. Rooting was also highly significantly affected (p<0.0001) by the temperature at the time of cutting. Rooting success of cuttings from seedling-derived parental hedges was similar to cuttings from coppiced stumps. The consequences of the low repeatability of measurements of rooting ability, 0.187 (S.E. 0.067) by clone and 0.340 (S.E. 0.072) by ramet, which was influenced by the response to age of material and nursery conditions, is discussed. This study demonstrated that large improvements in rooting success can be made by the optimization of rooting protocols and selecting for superior genotypes, as long as the performances of genotypes are accurately assessed.
Screening sweetpotato (Ipomoea batatas L.) for drought tolerance and high β-carotene content in Mozambique.
(2011) Ricardo, José.; Shanahan, Paul Edward.
Sweetpotato (Ipomoea batatas, L.) is one of the important sources of carbohydrates and economic income in Mozambique. As with most of the food crops in Mozambique, it is usually produced by small-scale farmers under dryland conditions. Despite the importance of the crop, the storage root yields are still low and it is difficult to keep planting material (vines) for the next planting season. One of the major challenges to production is drought stress. Drought stress affects sweetpotato by retarding aboveground growth, reducing total root yield, percentage of dry mass, and reducing the quality of the roots as a result of the increase in damage caused by the sweetpotato weevil (Cylas formicarius). The objective of this study was to identify sweetpotato genotypes tolerant to drought particularly amongst the orange fleshed types which can be used in breeding programmes to improve the drought tolerance of genotypes grown in Mozambique. To this end, 48 genotypes were evaluated in both field and greenhouse studies conducted at Umbeluzi Research Station (26º 03’ S, 32ºC 23’ E; 12 masl) located about 30 km from Maputo city. The field trial was a three replicate, α-design with split-plots. Genotypes were the wholeplot treatment factor and irrigation levels were the sub-plot treatment factor. The three irrigation levels imposed were: nonstressed plants irrigated from planting to 120 DAP; moderately stressed, plants irrigated until 60 DAP; and severely stressed, plants irrigated until 30 DAP. In the greenhouse trial the 48 genotypes were grown in wooden boxes arranged in a two replicate, randomized complete block design. The plants were exposed to water stress from 10 DAP to the end of experiment at 60 DAP. Genotypes were significantly different for all traits, namely: survival %, vine vigour, aboveground biomass, total and commercial root yield, total fresh biomass, harvest index, β-carotene content, % dry mass, dry mass yield, incidence of sweetpotato virus disease, and incidence of weevil damage. Irrigation levels were significant for the traits: survival %, vine vigour, aboveground biomass, total and commercial root yield, total fresh biomass, harvest index, β-carotene content, % dry mass, and dry mass yield. Irrigation levels were not significant for incidence of sweetpotato virus disease and incidence of weevil damage. The genotypes x irrigation levels interaction was significant for: total and commercial root yield, and incidence of weevil damage; and not significant for: survival %, vine vigour, aboveground biomass, total fresh biomass, harvest index, β-carotene content, % dry mass composition, dry mass yield and incidence of sweetpotato virus disease. The mean dry mass yields across irrigation levels of the national breeding lines and introduced genotypes were higher than the landrace genotypes. Most of the national breeding lines had higher β-carotene content than the introduced and landrace genotypes. The landrace genotypes had relatively higher % dry mass composition compared to the national breeding lines. The stress tolerance index (STI) separated the 48 sweetpotato genotypes evaluated in the field trial into three groups: drought tolerant (high STI); moderate drought tolerant (intermediate STI); and drought sensitive (low STI). Under moderate stress, yield potential (Yp) and yield in a stress environment (Ys) were highly significant, positively correlated with Mean productivity (MP), Geometric mean productivity (GMP), Stress tolerance index (STI) and Tolerance index (TOL). Under severe stress the same correlations were reported. Under moderate and severe stress, the correlation between stress tolerance index (STI) and Stress susceptibility index (SSI) was significant and negative. In the greenhouse trial, differences between genotypes in vine length increment, vine diameter increment, leaf width increment and number of nodes vine-1 were significant (P<0.05). Vine length, vine diameter, leaf width and length increments either increased or were reduced due to water stress. Less than 10% increment in vine length (between 25 and 50 DAP) was recorded in MGCl01, Atacama, Cordner, Beauregard, and CN1448-49. Higher than 40% vine length increment was recorded in Jonathan and UNK-Malawi, Naspot, MUSG0614-24, Resisto, K566632, Tainung64, Ejumula and MUSG0623-09. Vine diameter decreased in Manhissane and MUSG0616-18. No change in leaf length in Tacna and Jonathan and in leaf width in Xihetamakote and Resisto-Nairobi was recorded. The longest petiole length at 30 DAP was recorded by Tacna and the shortest by Nhacutse4. The longest internode length was recorded in 199062.1. Similar to petiole length, Nhacuste4 reported the shortest internode length. The highest number of primary vines was recorded by MUSG0608-61 and lowest by Beauregard. Of the 48 genotypes exposed to water stress, 18 survived until the end of the greenhouse experiment at 60 DAP and were therefore considered to be drought tolerant.
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.
Responses of ten soybean [ glycine max (L.) merrill] genotypes for yield and nodulation to trichoderma and silicon applications.
(2012) Jadoo, Shiksha.; Shimelis, Hussein Ali.; Laing, Mark Delmege.
A study was conducted to determine the responses of 10 selected soybean (Glycine max L.) genotypes to potassium silicate (KSi) and Trichoderma harzianum (Eco-T®) applications. Preliminary studies involving two independent experiments were conducted under controlled conditions at the University of KwaZulu-Natal during 2010. Potassium silicate at three concentrations (0, 200 and 250ppm) were applied twice weekly over a period of four months to the genotypes laid out in a randomized complete block design. Subsequently, a field experiment was conducted at Ukulinga Research Farm of the University of KwaZulu-Natal, Pietermaritzburg during 2010/2011 to investigate the responses of the genotypes to KSi at 0 and 200ppm, with and without(Eco-T®) seed treatment. This experiment was set out in a randomized complete block design with three replications. Data collected included number of days to 50% flowering, number of days to 50% maturity, plant height, number of pods per plant, number of seeds per pod, 100 seed weight, root mass, shoot mass, seed yield and harvest index. The total number of root nodules formed and the number of active nodules were determined at end of the field experiment. In most cases a decrease was noted in total nodule formation as well as a decrease in the number of active nodules that formed. In the controlled environments there was a significant interaction between genotype and KSi concentrations for all measured traits. In most cases KSi applied at 200ppm was more successful in enhancing growth, improving seed yield and resulted in high harvest indices. The genotypes that produced the highest seed yield and harvest index in these environments were Williams and Barc-2 at 200ppm KSi. Results from correlation analysis revealed that harvest index and seed yields were generally positively associated with plant height, number of pods per plant and 100 seed weight, which in turn were the traits that contributed to most of the variation to seed yield and harvest index as revealed in the principle component analysis (PCA). The field experiment revealed a significant interaction between genotype x KSi x Eco-T®. Potassium silicate applied at 200ppm with Eco-T® usually promoted growth, seed yield and high harvest indices for all the genotypes. The PCA showed seed yield and harvest index were the traits that contributed to most of the variation. Genotypes Williams, LS6161R, Magoye and Barc-2 were the best seed yielders with the highest harvest indices that responded strongly to the combined use of KSi and Eco-T® under field conditions. Genetic comparison of the ten soybean genotypes with eight microsatellite markers revealed the close genetic relationship between Williams, LS6161 R and Magoye. A link between Barc-2 and Williams was noted by the common parent Clark. Therefore, for these genotypes, the application of KSi at 200 ppm with Eco-T® under field conditions effectively increased seed yield, ranging from 0.45 to 65.26% for some genotypes when compared to the control. An increase was also noted for other agronomic traits and harvest index.
Genetic variation and associations among adaptive traits in a recombinant maize inbred line population.
(2012) Sithole, Mxolisi Percival Sibongeleni.; Derera, John.; Odindo, Alfred Oduor.
Maize production in Africa is constrained by abiotic and biotic stresses. Breeders need to have information on the nature of combining ability of parents, their traits and performance in hybrid combination. This requires careful determination of genetic variability of parents, and studying associations between grain yield and adaptive traits to breed superior cultivars which are better able to withstand such stresses. Therefore, this study was aimed at selecting parental testers with best combining ability in hybrid combination with recombinant inbred lines (RILs); and studying the correlation between grain yield and its components in eastern and western South Africa. It was also aimed at determining genetic variation and associations among adaptive traits in hybrids involving RILs. The final objectives of the study were to determine cultivar superiority of testcrosses involving RILs, and to select the best cultivars within and across four different environments. The 42 RILs were crossed to 9 Zimbabwean tropical testers resulting in 1009 hybrids with sufficient seed for planting in trials. From these a sample of 87 hybrids with adequate seed were selected and planted at four sites for combining ability analysis. The hybrids were evaluated at four sites in two regions; western region (Potchefstroom research station) and eastern region (Cedara, Ukulinga and Dundee research stations), during 2011/12 season. The experiments were laid out as augmented alpha lattice design. Trials were managed in accordance with production culture for each region. All quantitative data was subjected to GenStat and SAS statistical softwares. The results from combining ability study indicated that the line general combining ability (GCA) effects played a non-significant role (p > 0.05) in determining grain yield, grain moisture and anthesis date, while they were significant (p ≤ 0.05) for the other traits such as ear prolificacy. The tester main effects were significant for all the traits except ear prolificacy and plant height. Results also revealed that all the traits were controlled by both additive and non-additive genes, where additive gene action had the most contribution to the traits. The non-additive gene action played a minor role suggesting the total GCA effects attributed to both lines and testers predominantly higher over the specific combining ability (SCA) for all traits. In general the additive effects were preponderant over the non-additive gene effects. One cross (L114 x T12) had a significant and positive SCA effect for grain yield. The correlation between grain yield and secondary traits (number of ears per plant, grain moisture content, ear height, plant height, ear position and anthesis date) suggested that indirect selection can be employed to enhance grain yield by breeding for these particular adaptive traits. Path analysis showed that plant height had the highest direct and indirect effect on grain yield indicating its importance among other secondary traits for grain yield enhancement. Phenotypic coefficient of variation (PCV) was higher than genotypic coefficient of variation (GCV) for all the studied traits across all the four environments. All the traits displayed high heritability at Potchefstroom except anthesis date which was highly heritable at Ukulinga. Cedara was the second best site for heritability of all the traits except for the number of ears per plant. The genetic advance for grain yield was the highest at Cedara followed by Potchefstroom, Dundee and Ukulinga. The hybrids exhibited different patterns of variation and distribution for all the traits. This indicated that selection strategies to exploit GCA should be emphasised. Association studies among grain yield and secondary traits such as ear length, number of ears per plant, plant height, anthesis date, silking date and ear leaf area revealed that there were significant phenotypic correlations between grain yield and secondary traits, and among the secondary traits. Ear length had the highest direct effect on grain yield at Ukulinga; number of ears per plant had the highest direct effect on grain yield at Cedara and Potchefstroom; whereas plant height had the highest direct effect on grain yield at Dundee. Grain yield was least affected by indirect factors at all the sites except Ukulinga, where anthesis date had the highest indirect effect on grain yield through silking date followed by plant height through leaf area. The study reveals that there is significant variation among the hybrids for mean performance, indicating that there is opportunity for selection. Overall the findings suggest that direct selection would be appropriate to enhance grain yield. Path analysis revealed that plant height had the highest direct and indirect effects on grain yield, indicating that plant height can be further exploited as the main trait in future breeding programmes for grain yield increment. Hybrid 10MAK10-1/N3 was the best hybrid at Ukulinga in terms of grain yield, relative yield and economic traits. Whereas hybrid T17/L83 was the best hybrid at Cedara in terms of grain yield and relative yield; however, T11/L102 was selected as the most elite hybrid with respect to grain yield, relative yield and economic traits. Hybrid T3/L48 was identified as thebest hybrid at Dundee with respect to grain yield, relative yield and prolificacy. At Potchefstroom the standard check PAN6611 was identified as the best hybrid in terms of grain yield and relative yield followed by developmental hybrid T1/L28; however, developmental hybrid T1/L28 was the best in terms of earliness, prolificacy and ear aspect. Stability coefficients and cultivar superiority index across the sites revealed that four developmental hybrids were identified as best hybrids and they performed better than the standard check. These hybrids will be recommended for further testing in advanced trials. With respect to cultivar superiority, the desired hybrids are required to combine high grain yield with economic and adaptive traits such as high ear prolificacy, low grain moisture, and low ear aspect score (desired) for them to adapt to production environments in South Africa. There was significant variation among the top 25 yielding hybrids. At least 5 hybrids combined high grain yield with the desired complimentary adaptive traits such as quick moisture dry down, prolificacy and ear aspect. The results showed that there is variation in the performance of high yielding genotypes within all the sites, and that agronomically superior cultivars can be identified. The study shows that there is significant variation among the RILs since they interacted differently with the 9 tropical testers. Even among the top 25 selections of RILs in each environment there was still variation for combinations of the desired traits. Significant associations among grain yield and other economic and adaptive traits were observed with implications for breeding strategy. Above all the significant variation gives large score for future breeding of new unique lines.
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.
Genetic analysis of agronomic and quality traits in popcorn hybrids.
(2012) Jele, Collinet Phumelele.; Derera, John.; Siwela, Muthulisi.
Popcorn is increasingly becoming popular as a snack and is consumed widely all over the world. It is a high value crop, with possible multiplier effects like income generation for the under-resourced communities in the second economy. Despite its popularity, developing countries are battling to meet the demand and rely on importing popcorn grain due to challenges which include poor agronomic traits and slow breeding progress. Most of the imported varieties are not adapted to stress-prone local environments, which are prevalent in tropical sub-Saharan Africa. The objective of the study was to evaluate newly developed hybrids and inbred lines for agronomic and popping quality traits with the possibility for commercialization in future. The study aimed at determining variability for popping ability in inbred lines and hybrids, grain yield and its secondary traits, the nature of gene action, relationships among agronomic and popping quality traits, effect of genotype x environment interaction on agronomic traits and popping method x genotype interaction effects. To determine popping ability, 128 inbred lines were evaluated at the University of KwaZulu-Natal, South Africa, in June 2011 using two popping methods, the microwave method and the hot-air method. The popping quality attributes measured were flake volume, popping fold, number of unpopped kernels, kernel size and quality score. Variability among inbred lines was significant (P<0.05) for all traits. Flake volume ranged from 63 cm3 to 850 cm3, popping fold ranged from 2.5 to 34 times the original volume. Kernel size had a significant positive correlation (r= 0.49) with the number of unpopped kernels. There was a significant strong and negative correlation between flake volume and the number of unpopped kernels (r= -0.62), indicating that either of the two traits would be effective for measuring popping ability. Experimental hybrids were then developed from 87 out of the possible 128 inbred lines. Only the inbred lines with sufficient seed were crossed to develop hybrids. Random crosses were generated at Makhathini Research Station during the winter season of 2011. Crosses were made at random among parents that managed to synchronize their flowering dates, resulting in 119 hybrids with sufficient seed for planting in trials. To determine agronomic superiority, the 119 experimental hybrids and the standard check P618 were evaluated at the Cedara Research Station and Ukulinga Research Farm in the Midlands of KwaZulu-Natal during the summer of 2011/2012. The experiments were laid out as 10 x 12 alpha lattice design, with two replications at each site. Standard cultural practices for maize were followed. The data were subjected to analysis of variance and line x tester analysis in Genstat and SAS statistical programmes. Results indicated that hybrids were significantly different for all agronomic traits. Means for grain yield ranged from 1.0 t/ha to 5.2 t/ ha. General combining ability effects were significant for all agronomic traits, suggesting that additive gene effects were governing these traits. Specific combining ability effects were significant for ear length, number of ears per plant and yield indicating, that non-additive gene effects were influential for these traits. Generally, agronomic traits were highly heritable. Grain yield showed significant and positive correlation with ear length, plant height, ear position, shelling percentage and number of ears per plant, indicating that these were the major yield-determining secondary traits which should be enhanced in popcorn. Although site main effects were highly significant for secondary traits, the hybrid x site interaction was not significant. The results therefore indicate that the hybrids were ranked similarly at both sites. The 119 experimental hybrids and the standard check P618 were evaluated for popping quality, using the microwave and the hot-air popping method. There was a significant variability observed among hybrids for popping quality traits. Flake volume across sites and across popping methods ranged from 734 cm3 to 1288 cm3. Popping fold ranged from 14.69 to 25.75 times the original volume. Additive gene action was more prominent than non-additive action for all popping quality traits. The SCA effects were significant for flake volume, popping fold and number of kernels per 10 g. All popping quality traits had high heritability, indicating that selection would be effective to improve popping. Flake volume was negatively correlated to quality score, indicating that popping expansion is reflected on the quality score and a significant negative correlation between flake volume and number of unpopped kernels. There was significant and strong positive correlation between kernel size and number of unpopped kernels. Hybrid x site interaction was only significant for quality score and kernel size. Hybrid x method interaction was not significant, indicating that popping ability was not dependent on the method. Inbred lines showed significant variation for popping quality and therefore have utility for hybrid development. Significant genotypic variation was also observed among hybrids for agronomic and popping quality traits. Additive gene action was predominantly responsible for both agronomic and popping quality traits. Both agronomic and popping quality traits were highly heritable and positive relationships were identified among traits. Overall, the study indicates opportunities for further breeding progress through selection.
Why SR52 is such a great maize hybrid.
(2013) Musimwa, Tatenda Rambi.; Derera, John.
Maize is Africa’s most important food crop. Unfortunately a yield gap currently exists in Africa which can be attributed to the use of inferior maize varieties such as open-pollinated varieties, double and three-way cross hybrids. Single cross maize hybrids, such as the world’s first commercial hybrid, SR52, have a higher yield potential, which is reflected by the doubling of maize yields in southern and eastern Africa by SR52, within a decade of its release. The main objective of this study was to determine the genetic basis behind SR52’s high yield potential and heterosis. This was established through a generation mean and path coefficient analysis of the SR52 maize hybrid. Research to determine genetic basis of yield and secondary trait was conducted using a randomized complete block design at two sites during the 2012/13 season, in South Africa. Six derivative generations of SR52 namely, its two parents N3 and SC, F1 and F2, and F1 backcross progenies (BC1N3 and BC1SC) were evaluated. A generation mean analysis was performed using PROC GLM procedures in SAS computer software program. High levels of mid-parent heterosis for grain yield potential was confirmed and ranged from 140% at Cedara to 311% at Ukulinga. The additive-dominance model was not adequate to explain the yield potential of SR52. Although negligible (less than 10%), epistatic gene effects were also influential (P<0.01) on grain yield and its components in SR52. The dominance and additive gene effects were highly significant (P<0.01), but dominance effects were the most influential. Correlation and path coefficient analysis of SR52’s segregating F2 and BC1 populations was performed in SAS. Most secondary traits, such as ear mass, ear length, total number of kernels per ear and plant height, were significant (P<0.05) and positively correlated with yield. However, the ear length, number of kernel rows, kernels per row and 100-kernel mass displayed the largest direct effects on yield of SR52, while indirect effects of secondary traits were small. The presence of genetic variation, as well as transgressive segregants for the yield components indicates possibility for extracting new germplasm lines with the desired QTL’s. It is concluded that SR52 is such an exceptional hybrid because of dominance gene action and direct contribution of superior cob length, number of kernel rows and mass of kernels to yield.
Heterosis, genetic distance and path coefficient analysis in dent, flint and popcorn hybrids.
(2013) Mhoswa, Lorraine.; Derera, John.; Odindo, Alfred Oduor.
Maize (Zea mays L.) is one of the most important food crops in sub-Saharan Africa (SSA); however its production is constrained by many factors. Grain yield is compromised by poor genetic performance and poor agronomic management. This calls for need to develop hybrids and exploiting heterosis of single crosses which are adapted to challenging environments. Currently, there is no popcorn hybrids developed in South Africa which is adapted to local conditions. As such, there is need to develop hybrids that cater for smallscale farmers in marginal environments. The objectives of the study were to determine i) standard heterosis, levels of variation and heritability for phenotypic traits in dent and flint maize hybrids; ii) the association between genetic distances and phenotypic traits in dent and flint maize hybrids; iii) mid-parent heterosis in popcorn hybrids, iv) the effect of secondary traits on grain yield in dent, flint and popcorn hybrids; v) genetic diversity and the relationship between traits in widely grown selected hybrids in Southern Africa; and vii) to compare effectiveness of phenotypic analysis models for determining genetic distances between hybrids. Popcorn, dent and flint hybrids were evaluated at two sites. The data was analysed using SAS, Genstat and Power marker statistical packages. The results revealed that the relationship between genetic distance and heterosis is dependent on the environment. Hybrids in top 10 at both sites were different indicating that there was a significant genotype x environment interaction. 13 new heterotic patterns that performed better than the controls can be utilized in heterosis breeding; however there is need to test them in different environments to check on their stability. Grain texture cannot be used to discriminate hybrids for yield because all patterns of dent x dent, dent x flint and flint x flint were present in the top 10 hybrids. Lines DXL124 and DXL158 dominated parentage of the top 10 hybrid rank for yield qualifying them as potential testers for specific combining ability in future studies. Heterosis in popcorn hybrids that performed better than the mid-parent can be utilized in heterosis breeding to exploit vigour, though there is need to test the hybrids in a number of different environments. The main direct factors contributing to yield were ear prolificacy, ear aspect, number of plants and shelling percentages qualifying them to be selected to boost grain yield. Phenotypic data and 91 SNP markers were used to estimate the genetic distance between the hybrids. The results indicated that hybrids that were in the same cluster belong to the same brand and were related in origin and pedigree. Both molecular and phenotypic data were effective in discriminating the hybrids into different clusters according to genetic background. SNP markers revealed nine clusters of hybrids, 12-trait model revealed eight clusters and five-trait model revealed six clusters at 85% genetic distance. The study indicates strategies that can be adopted to boost grain yield in dent, flint and popcorn hybrids.
Genetic and economic value of a shuttle breeding programme for enhancing adaptability of tropical maize germplasm in South Africa.
(2013) Musundire, Lennin.; Derera, John.; Tongoona, Pangirayi.
Maize is the principal crop for food security and livestock feed in South Africa. It is also an industrial crop and the produce is exported to many countries in the world. Therefore there is high seed demand which prompts competition for breeding productive hybrids. However direct introduction of tropical hybrids into the warm temperate South African environments has not been successful. Competitive advantages can be obtained by implementing a “shuttle breeding” programme whereby part of the breeding is done in Zimbabwe and South Africa to minimise research and production costs. Introgression of temperate germplasm in tropical elite inbred lines can also be pursued to obtain adapted hybrids. The aim of this study was therefore to assess the effectiveness of introgression of temperate germplasm into tropical elite maize inbred lines as a strategy to enhance adaptability of new hybrids to South Africa, and also to determine both breeding and economic value of a “shuttle breeding” programme. To this end, the introgressed inbred lines and their hybrid progenies were evaluated in South Africa to determine the effect of the selection environment on their performance and genetic variation. Both genetic and economic gains were evaluated with a view to make recommendations to the small and medium scale enterprises with interests in the market. Introgression of temperate germplasm into tropical germplasm elite lines did not disrupt the heterotic groupings because most of the introgressed lines (86%) fitted into known existing heterotic groups. Only 14% of the introgressed lines did not show any inclination to towards the known heterotic clusters of their founder tropical parents. These lines were considered to be new recombinant inbred lines that showed little resemblance with their founder parents. Selection environment did not influence heterotic clustering of the introgressed lines, and genetic diversity was identified among introgressed lines developed in the same environment. Genetic variation was observed for the major economic traits and heritability of 21% to 91%. The introgression was effective for improving grain yield potential and ear prolificacy. Spearman’s rank correlation analysis on grain yield and ear prolificacy data showed significant positive correlation between selection environments such as Ukulinga in South Africa and Kadoma Research Centre in Zimbabwe. Therefore Kadoma Research Centre will be recommended for use in breeding new maize germplasm lines for South Africa. Correlation among traits showed that ear prolificacy and plant height had significant (P<0.05) direct effects on grain yield thus direct selection of these traits will be emphasised in breeding new hybrids. Introgression of temperate germplasm into tropical elite maize inbred lines was effective for improving their adaptation to warm temperate environments. Positive genetic gains of 5-58% were realised for grain yield potential and 26-46% for ear prolificacy. Whereas 1% to 37% gains were realised for secondary traits such as plant and ear height, anthesis and silking days there was barely any improvement for root and stalk lodging, and grain moisture content at harvest. However, introgressed lines displayed impressive performance per se and inter se indicating potential for commercial production. The new inbred line 71-DMLF7_88 combined early physiological maturity, high ear prolificacy and grain yield potential qualifying it as a perfect parent for the warm temperate environments. At least six hybrids were stable and adaptable while four were considered to be ideal genotypes relative to standard commercial hybrids such as PAN6Q445B which is a market leader. The exceptional hybrids, 12C20264, 12C22766, 13XH349 and 11C11774 will be advanced in South Africa. The study also indicated significant economic gains when a shuttle programme is implemented to breed new hybrids following the introgression strategy. The “Shuttle breeding” programme attained a positive net present value (NPV) of $1, 834, 166. 00. This indicated an increase in shareholder value through an opportunity cost of 17% and 3% relative to conventional breeding programmes which are based in South Africa and Zimbabwe, respectively. Positive NPV and genetic gain achieved using the “shuttle breeding” programme makes it a viable option for small and medium scale seed companies with intention to breed and commercialise competitive products in South African. In general, the study revealed that introgression of temperate germplasm into tropical elite inbred lines using a “shuttle breeding” programme was effective for enhancing adaptability of tropical germplasm to the South African warm temperate environments.
Genetic analysis of stem rust resistance among Ethiopian grown wheat lines.
(2014) Hei, Netsanet Bacha.; Shimelis, Hussein Ali.
Wheat (Triticum aestivum L.) is one of the major food crops in the world. Ethiopia is the second largest wheat producer in sub-Saharan Africa. However, wheat production in Ethiopia is constrained by many biotic and abiotic factors, and socioeconomic constraints. Among the biotic stresses are the rust diseases: stem rust caused by Puccinia graminis f.sp. tritici, leaf rust (P. triticina Eriks) and stripe rust (P. striiformis Westend. f.sp. tritici)). Stem rust is considered to be the most destructive disease of wheat in the main wheat growing regions of Ethiopia. Losses may reach 100% on susceptible wheat cultivars when conditions are favorable for disease development. Use of resistant cultivars is the most effective, economical and environmentally safe control measure, especially for the resource poor farmers. Due to the frequent emergence of new stem rust races through mutation, migration and recombination of exsisting virulence genes, efforts to identify potentially new sources of effective resistance genes are of the highest importance followed by their incorporation into a desirable genetic background. The objectives of the study were 1) to identify the primary threats to wheat production, farmers’ selection criteria for wheat varieties, and disease management practices with emphasis on wheat rusts in the Arsi, Bale and West Shewa administrative zones of Ethiopia; 2) to identify possible sources of stem rust resistance among Ethiopian wheat lines; 3) to determine the levels of heterosis and combining ability, and to identify the best parents and crosses for breeding to stem rust resistance, high grain yield and desirable agronomic traits; 4) to introgress durable resistance genes from known resistance sources into farmers’- preferred and locally adapted but stem rust susceptible, improved wheat varieties. A participatory rural appraisal (PRA) research was conducted involving 270 farmers in six districts of three administrative zones in Ethiopia. The participating farmers listed and prioritized their wheat production constraints. Wheat rust diseases, the high costs of fertilizers, lack of access to seeds of improved varieties and high seed prices were the major constraints reported by the respondents. The most important traits that farmers sought in wheat varieties were disease resistance and high grain yield. Estimated yield losses due to stem rust disease were more than 60% in all the surveyed areas. Fungicide application was the main disease management practice used by the majority of respondent farmers. Field and greenhouse experiments were conducted to identify possible sources of stem rust resistance among Ethiopian wheat lines. Two hundred fifty two wheat genotypes were evaluated for their resistance to stem rust at the seedling stage. Ninety one lines that exhibited intermediate and susceptible seedling reactions were field tested for their slow rusting characteristics. Among the 91, 38 lines that had high to moderate level of slow rusting were advanced to further field evaluation. Ten lines (H04-2, 204408-3, 214551-1, 231545-1, 7041-1, 7514-1, 226385-1, 226815-1, 7579-1, and 222495-1) were identified as good slow rusting lines while seven (237886-1, 227059-1, 203763-1, 226275-1, 227068-2, 226278-1 and 7994-1) were identified as moderately slow rusting lines. Fifteen wheat hybrids were developed through a half diallel mating design involving six parents. The F1’s and their parents were field evaluated for their stem rust reaction and agronomic performances at the Debere-Zeit Agricultural Research Center in Ethiopia, which is a well known hot spot area for stem rust. The analysis of variance revealed that tested genotypes had considerable genetic variability for all characters studied. The maximum positive mid-parent (31.45%) and betterparent heterosis (25.38%) were observed for grain yield. Plant height and days to maturity had maximum negative mid-parent heterosis levels of -11.01% and -8.02%, respectively. The majority of the crosses expressed negative heterosis over their mid-parent for AUDPC, indicating these crosses manifested resistance against stem rust. Significant general combining ability (GCA) effects were observed for all the characters studied. Furthermore, significant specific combining ability (SCA) effects were detected for most of the traits. Non-additive gene action was predominant for grain yield, thousand kernel weight and plant height. Additive gene action played a greater role in the inheritance of AUDPC, kernels per spike, number of tillers per plant and days to maturity. The study identified parental lines with good GCA effects for most of the characters, especially H04-2, Digelu and Danda’a. Crosses 231545- 1 x H04-2, 7041-1 x H04-2, Digelu x Kubsa and Danda’a x Kubsa had significantly negative SCA effects for AUDPC. Progenies of these crosses will be selected in an ongoing stem rust resistance breeding program. In general, H04-2 and Danda’a were good general combiners for most of the important studied characters. Crosses that involved these lines performed well for most of the traits. Hence, Lines H04-2 and Danda’a could be exploited in wheat breeding programs to develop stem rust resistant and high yielding wheat cultivars. Stem rust resistance genes were introgressed into locally adapted, high yielding susceptible wheat varieties, Kubsa (HAR1685) and Galama (HAR604), from two sources of adult plant resistance, Pavon 76 and Kenya Plume, using the single backcross-selected bulk breeding approach. The resistance sources were crossed with the adapted high yielding varieties and a single backcross was made with the recurrent parent. The resulting BC1 populations were selfed until the F3. Bulk selection was practiced from BC1- F3. The F3 populations, along with the recurrent parents, were evaluated in a replicated trial at Debre-Zeit Agricultural Research Center under high stem rust pressure to determine the genetic improvement attained in the populations for stem rust resistance and agronomic traits. All F3 populations, except the cross of Galama x Kenya Plume, were better performing for stem rust resistance and most agronomic traits studied when compared to the recurrent parents. The F3 progenies of Kubsa x Pavon 76 had superior mean values and high genetic gains for most agronomic attributes and stem rust resistance. These progenies will be advanced and selected in subsequent generations to develop locally adapted pure line wheat varieties with improved stem rust resistance and farmers’-preferred agronomic traits. Overall, the present study attempted to understand farmers’ wheat varietal preferences, farmers’ wheat production constraints, identified slow rusting wheat lines among the Ethiopian bread wheat germplasm, identified promising lines and F1 hybrids with good combining ability for breeding towards stem rust resistance and high yields. Durable stem rust resistance genes were incorporated into locally adapted susceptible wheat varieties for further selection and future release to enhance wheat productivity in Ethiopia.
Introgression of aflatoxin and fumonisin contamination resistance genes in maize hybrids.
(2014) Chiuraise, Nyashadzashe.; Derera, John.; Yobo, Kwasi Sackey.
Maize is the principal crop in Africa, particularly in southern Africa. However, food security in the region is constantly threatened by the contamination of maize grain through mycotoxins, such as aflatoxins and fumonisins caused by Aspergillus flavus and Fusarium verticillioides, respectively. Food security is defined as the capacity of a nation to ensure that all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life. Aflatoxins and fumonisins are carcinogenic, teratogenic, mutagenic and immunosuppressive to both humans and livestock. Presently, breeding for reduced mycotoxin contamination is one of the best strategies to reduce aflatoxin and fumonisin contamination in maize grain. Although mycotoxin resistant maize inbred lines have been identified, currently, there are no aflatoxin and fumonisin resistant commercial maize hybrids available to farmers in southern Africa. Decades of research have resulted in the identification of maize inbred lines that are resistant to either aflatoxin or fumonisin accumulation but not to both. Therefore the current study aimed at stacking resistance genes to the two toxins in one germplasm line or hybrid. The first objective of this study was to determine the current picture of mycotoxin contamination in southern African maize germplasm. Thus, a survey on South African and regional experimental hybrids was carried out during 2012/13 and 2013/14 seasons to determine the natural incidences of different types of ear rots and to identify the associated fungi. The second objective was to stack the resistance genes in a single product through introgression of aflatoxin and fumonisin resistance genes from tropical inbred lines into adapted inbred lines used in the subtropical and temperate conditions of southern Africa. Consequently, the resultant 72 single cross hybrids were evaluated for fumonisin contamination and 44 three-way cross hybrids and their progenies (146 S2:3 families) were evaluated for both aflatoxin and fumonisin contamination under artificial inoculation, in South Africa. Survey results showed that F. verticillioides was the most prevalent ear rot causing fungi followed by Stenocarpella maydis, Fusarium graminearum and A. flavus. These pathogens have potential to cause fumonisins, dipliotoxins, vomitoxins and aflatoxins. Assessment of experimental hybrids indicated a significant variation (P <0.001) among hybrids for ear rot incidence, and contamination by mycotoxins. Five single cross hybrids accumulated consistently low fumonisin levels (<4 ppm) both in the greenhouse and field trials. Three 3-way cross hybrids displayed a combined low contamination level for both aflatoxins (<5ppb) and fumonisins demonstrating potential for stacking resistance genes in the end product. Four S2:3 families also accumulated low levels of both aflatoxins and fumonisins below the legal limits of 5 ppb and 4 ppm, respectively, further demonstrating that new maize inbred lines can be developed by stacking mycotoxin genes. Therefore the study indicated a significant progress towards breeding mycotoxin resistant hybrids. Recommendations for upscaling this achievement are discussed.
An investigative study of the drought tolerance of F1 maize (Zea mays L.) single crosses derived from PANNAR and CIMMYT inbred lines.
(2015) Muyambo, Caiphas.; Shanahan, Paul Edward.
Drought is the most devastating abiotic stress limiting the production of maize (Zea mays L.) worldwide. The effect of drought stress is greatest in sub-Saharan Africa (SSA) where most small scale farmers rely on open pollinated varieties (OPVs); rather than certified hybrid seed grown under dryland1 conditions. Small scale farmers perceive OPVs to be drought tolerant and yet the yields are as low as 1-2 t ha-1 . In many parts of SSA, therefore, hybrid adoption rate is still below 20%. With the projected population growth in SSA, food insecurity is likely to worsen. However, the development of drought tolerant maize hybrids to help address declining food security is a relevant strategy in SSA. This is so because, drought tolerant hybrids will out yield OPVs. The main objective of this study was to investigate the drought tolerance of F1 single cross maize hybrids developed from CIMMYT drought tolerant donor inbred lines and PANNAR elite inbred lines. The hybrids were tested under random and managed drought stress environments. The first set of F1 hybrids was produced using a 12x12 North Carolina factorial mating design during winter (April-August 2012) and the second set of hybrids was produced in summer (November 2012-March 2013). Seventy F1 hybrids were tested during the summer season (November 2012- April 2013) under random drought stress (RDS) environments in South Africa and Zimbabwe. One hundred hybrids were tested during the winter season (April – September 2013) in Zimbabwe at CIMMYT experimental stations in Save Valley and Chisumbanje under managed drought stress (MDS). The main traits measured included grain yield (GY), ear plant-1 (EPP), anthesis-silking interval (ASI) and days to anthesis (DTA). Statistical analysis of collected data was conducted using GenStat 16th edition. Significant differences between hybrids and environments for grain yield and secondary traits were obtained. The genotype x environment (GxE) interactions was significant under both RDS and MDS environments indicating the differential performance of hybrids across environments. Using stability indices, the relatively stable hybrids were identified. General and specific Combining ability (GCA and SCA) analysis revealed lines that could be used as potential parents in development of hybrids. However, the presence of GCAxE and SCAxE interactions indicated that selection of inbred lines and their hybrid crosses should be done at target environments. Under RDS and MDS, EH79 and EH24 appeared to be the best performing hybrids, respectively, whereas inbred lines DT2, DT7 and UT8 had the best GCA and SCA under both RDS and MDS. Further efforts are required to develop potential drought tolerant hybrids and test for adaption in target environments.
Phenotypic characterization of mycotoxins resistant maize inbred families and regional hybrids under Aspergillus flavus and Fusarium verticillioides infestation.
(2015) Masemola, Bogaleng Milcah.; Derera, John.
Most South African households depend on maize as source of their staple food and daily calories intake, especially the rural communities which depend on the crop to maintain their livelihood. Despite the importance of maize, numerous factors either biotic or abiotic factors affect its production worldwide. Ear rot is one of the common diseases that affect maize production and productivity worldwide. Aspergillus flavus (Raper and Fennel) and Fusarium verticillioides (Sacc.) are two of the serious ear rot-causing maize fungi. These fungi secrete mycotoxins which are hazardous when consumed by humans or animals. The study was executed to characterize mycotoxins resistant maize inbred families at the phenotypic level and to determine the level of natural incidences of ear rot diseases which are associated with mycotoxins contamination. Understanding architecture of genetic of these resistant maize inbred families would greatly aid in breeding high yielding and stable ear rot and mycotoxins resistant hybrids. Experimental trials were conducted at Ukulinga and Cedara Research Stations, during the 2014 to 2015 growing seasons. Further evaluation was conducted at the Makhathini Research Station during the winter season of 2015. The study was conducted using two experiments. The first experiment was assessment of natural ear rot incidences on regional maize hybrids. These hybrids represented a sample of varieties which are grown in the Southern African region. In the second experiment, S3:4 families, which were derived from three way crosses among, A. flavus and F. verticillioides resistant maize families, were artificially inoculated with A. flavus and F. verticillioides. Grain yield and agronomic traits were measured in both experiments. The grains were evaluated for ear rot infection at harvest. The analysis of variance and correlation analysis were conducted using Genstat 14th edition (Payne et al 2007) and Agronomix Generation II (2000), while the multivariate analyses were conducted using the NCSS (2004) statistical computer program. The assessment of natural ear rot incidences on regional hybrids revealed that ear rot causing fungi is a challenge. The results revealed four fungi that were responsible for the natural incidences of ear rots. The fungi included A. flavus (Raper and Fennel), Stenocarpella maydis (Berk.), Fusarium graminearum (Schwein.) and F. verticillioides (Sacc.). Incidences of F. verticillioides were the highest during the two seasons. This might be due to hot dry weather conditions that occurred after flowering. Early maturing hybrids showed lower incidences of ear rots than hybrids that matured late. Although early maturing hybrids encountered less incidences of mycotoxin causing fungi, the results revealed early maturity period had a significant strong negative correlation with grain yield. This trend was consistent with previous studies. Phenotypic characterization study revealed a significant variability among the mycotoxins resistant maize inbred families for resistance to Aspergillus ear rot, Fusarium ear rot and other selected secondary traits except husk cover, insect damage and days to mid maturity. Generally heritability (H2) estimates were large for most traits, indicating an opportunity for selection of the best inbred families for advancement in the breeding programme. Plant height, ear height and primary tassel branches recorded higher heritability values (>80%) compared to the other traits. This was followed by Fusarium ear rot and Aspergillus ear rot resistance scores (≥77%) and grain yield (73%). The results revealed five principal components contributing more than 69% of the total variation and the traits responsible to this variation are Fusarium ear rot, Aspergillus ear rot, plant height, ear height, days to mid maturity, husk cover, insect damage and primary tassel branches. The inbred families were grouped into five principal component groups based on their phenotypic characteristics. Lines to be derived from these grouped families would be exploited to make heterotic combinations by crossing lines from the different phenotypic clusters.
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.

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