Browsing by Author "Chigeza, Godfree."

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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.
Genetic gain, advanced cycle pedigree breeding and correlated response to selection under varying moisture conditions in sunflower.
(2013) Chigeza, Godfree.; Shanahan, Paul Edward.
Sunflower (Helianthus annuus L.) is one of the most important oil crops in South Africa and genetic improvement for grain yield and oil-content was initiated in the country in the early 1970s. Commercial production of sunflower in South Africa is done under natural rainfall conditions in areas where frequencies of drought are high hence the requirement for drought tolerant cultivars. An assessment of the genetic gains in seed and oil yield achieved since 1970, the effects of re-cycling inbred lines and strategies for developing drought tolerant sunflower cultivars has not been done for South African sunflower breeding programmes. Two data-sets were used for the genetic gain studies: side-by-side evaluation of historical and current sets of popular cultivars in the same environment under one set of trial management practices; and yield trends in commercial farmers’ fields based on annual production estimates. The estimated relative genetic gain for seed yield based on side-by-side trials was 1.5% year−1 and the relative gain in seed yield per year under commercial production was 1.9% year−1. The contribution of new cultivars to total seed yield progress in sunflower were 56.3% for the period 1970 to 1989; 23.9% from 1990 to 2009 and the mean over the four decades under consideration from 1970 to 2009 was 41.6%. Quantifying the usefulness of inbred lines in advanced cycle plant breeding was done using four base breeding populations based on: phenotypic or genetic variability; heterosis; and combining ability. Significant genetic variation was evident for seed yield and oil yield while genetic variability for oil content was low. Genetic advance (GA%), with a 10% selection intensity, was high for seed yield and oil yield for each of the four populations ranging from 36-42% and 38-43%, respectively. The GA% for oil content was low ranging from 1.3% to 5.1% indicating the need to introgress high oil content germplasm in the present breeding populations in advanced cycle pedigree breeding. Founder parent heterosis (FPH), mid-standard heterosis (MSH) and high standard heterosis (HSH) indicated that some new testcross hybrids from the advanced cycle pedigree breeding populations were performing better than their founder parents in hybrid combination as well as the standard commercial hybrid checks. From variance component analysis, general combining ability (GCA) was predominant over specific combining ability (SCA) for seed and oil yields indicating that superior hybrids can be identified based on positive and significant GCA effects of the female lines. For oil content, SCA was predominant over GCA indicating that it would be best to select for specific hybrids combinations with high oil content rather than selecting female lines with high GCA effects. Variable moisture conditions characterise the sunflower production environments in South Africa. Breeding for such environmental conditions requires a combination of strategies including use of secondary traits and developing appropriate test environments. Three secondary traits, head diameter, stem diameter and stay green canopy which are easy to measure in the field were evaluated for their appropriateness for selecting for drought tolerance under three moisture conditions: random stress environments (RSE), managed drought stress environments (MSE) and well watered nonstress environments (NSE). Type A genetic correlations indicated that stay green canopy (SG) had the potential to be used as secondary trait to indirectly improve oil yield under the three moisture conditions. The indirect selection efficiency (ISE) for SG using genetic correlations based on H2 were 0.79, 0.82 and 0.78 in the RSE, MSE and NSE, respectively, while that using genetic correlation based on h2 were 0.67, 0.98, and 0.93 in the RSE, MSE and NSE, respectively. In both cases selection in the MSE had the highest efficiency using genetic correlations based on either H2 or h2. Estimates of indirect selection based on type B genetic correlations indicated that indirect selection for oil yield (OY) in the MSE and NSE for the target RSE was as effective as direct selection of OY in the RSE based on additive genetic correlations of 0.96 obtained in both selection environments. Overall, the results from the exploratory drought tolerance study should inform the development of breeding strategies to improve drought tolerance and associated yield stability of sunflower cultivars grown in South Africa and associated environments.
Genotypey by environment interaction, genetic variability and path analysis for grain yield in elite soybean [Glycine max (L.) Merrill] lines.
(2018) Mwiinga, Bubala.; Sibiya, Julia.; Chigeza, Godfree.
Soybean [Glycine max (L.) Merrill] is the world’s leading source of protein and vegetable oil. However, its productivity is still low in the region due to limited availability of stable and high yielding cultivars. Therefore, the objectives of this study were: (1) to determine the magnitude of genotype by environment interaction and stability of elite soybean lines for seed yield, (2) to establish trait profiles of 25 soybean genotypes and to study the associations among characters, their direct and indirect effects on grain yield and (3) to estimate genetic parameters of traits related to seed yield and to analyse genetic diversity among elite soybean lines. To achieve these objectives, 25 genotypes (20 elite soybean lines and five commercial checks) were evaluated in multi-location trials conducted in the 2017/18 rainy season using six sites in four countries viz. Zambia, Malawi, Zimbabwe and Mozambique. Both AMMI and GGE biplot analyses indicated Lusaka West as the highest yielding and most informative environment and could be useful for selecting specifically adapted genotypes. Rattray Arnold Research Station was the most ideal environment as it was both informative and highly representative. The soybean lines TGx2002-17DM, TGx2001-10DM, TGx2001-18DM, TGx2014-24FM, TGx2001-6FM and TGx2002-3DM exhibited specific adaptation. Both GGE and AMMI models showed that TGx2014-5GM was more stable than the checks and was second to the highest yielding check. The genotype by trait (GT) and correlation coefficient analyses revealed that pod number per plant and hundred seed weight were the most positively correlated traits with grain yield, while days to 50% flowering had a negative association with grain yield. Sequential path analysis, showed that the number of pods per plant and hundred seed weight had the highest positive and significant direct effects on seed yield, implying that these two traits could be used as selection criteria for seed yield in soybean. The soybean lines TGx2014-5GM and TGx2002-23DM had good combinations of high yields with large seed size and high pod number. The analysis of genetic variability showed small differences between PCV and GCV values for all the traits except for pod clearance. This implied that there were minimal effects of the environment and high contribution of the genes in the phenotypic expression of the traits, except for pod clearance, which was more affected by the environment. Moderate GCV values of 13.45% and 13.49%, high heritability values of 70% and 69% and GAM values of 23.24% and 23.04% were recorded for grain yield and number of pods per plant, respectively. Only two principal components, PC1 and PC2 accounted for the variation, with a cumulative contribution of 68.25%. All the seven traits were useful in discriminating the genotypes as they had high eigenvalues in either PC1 or PC2. The 25 soybean genotypes were grouped into two main clusters, which were further sub-divided into eight sub-clusters based on the seven morphological characters. The genotypes TGx2014-5GM, checks SC Safari and SC Squire in sub-cluster 6 had the highest means of the most desirable traits (large seed size, high pod number per plant and seed yield). The three genotypes could be used in hybridisation programmes for improvement of grain yield, seed size and number of pods of the genotypes. Overall, the study identified soybean lines that could potentially be released as cultivars in the four southern African countries or used as parents in future soybean improvement programmes. It also revealed traits that could be used for indirect selection of seed yield and high genetic diversity among the genotypes for possible exploitation in soybean breeding programmes to increase seed yield.
Study on grain yield stability, molecular diversity and multi-trait relationships among elite soybean lines.
(2018) Kachala, Bertha Mwayi.; Chigeza, Godfree.; Sibiya, Julia.
The demand for soybean production has increased in recent years, due to its multipurpose use for human food, livestock feed and industrial purposes. The soybean crop is one of the important source of oil and protein of the world, and is used as a source of high quality edible oil and protein. For a quantitative trait, yield is known to be influenced by changes in the environment in which the crop is grown, suggesting the need to evaluate soybean lines in different growing regions to assess their adaptability and stability. In plant breeding, selection is one of the most important stages in the breeding cycle. Multi-location testing of soybean genotypes precedes selection while genetic characterisation of germplasm enhances selection due to the variation realised and it is the basis for genetic improvement. The objectives of the study were: 1) to determine yield stability and adaptability of elite soybean lines across six locations, 2) to study genotype by trait associations and multiple trait relationships among soybean elite lines across six locations and 3) to assess the level of genetic diversity among the soybean elite lines using single nucleotide polymorphisms (SNP) markers. The stability and adaptation study was carried out to investigate genotype by environment interaction (GEI) for grain yield of 26 elite soybean lines along with four checks grown in 6 environments spreading across three countries (Zambia, Malawi and Mozambique) in a 6 x 5 alpha lattice design. The additive main effect and multiplicative interaction model (AMMI) indicated that environments, genotypes and GEI significantly affected grain yield (P<0.001) and contributed 3.8%, 17% and 78%, respectively, to the total variation. Three AMMI interaction principal components (IPCA1, IPCA2 and IPCA3) were significant (P<0.01). Genotype plus GEI (GGE) biplots were created based on the first two principal components, PC1 and PC2, which accounted for 39.23% and 26.86% of genotype plus GEI variation, respectively. The GGE biplot analysis ranked the genotypes for yield and stability, and environments for representativeness and discriminativeness. The relationships between genotypes and environments were also demonstrated. Genotype TGX 2001-3FM was identified as the ideal genotype with high yield mean performance and high stability. Therefore, it could be recommended for cultivar release if the study can be repeated to verify these findings. Chitedze in Malawi was the most informative test environment hence it is ideal for selecting generally adapted genotypes. Genotypes TGX 2002-4FM and TGX 2001-15DM were low yielding but with high stability hence can be recommended for further improvements. For the second objective, a study was conducted using 30 genotypes to determine the correlation and path coefficient of secondary traits on yield. The genotype by trait biplot is a tool that graphically compares genotypes on the basis of multiple traits and graphically visualises trait relationships, and genotype-trait associations. Trait profiling of genotypes through genotype-trait association analysis helps in making decisions on which genotypes to use as parents for a breeding programme. Significant differences among genotypes were observed for all studied traits. Correlation coefficient analysis presented that grain yield had a significant and negative correlation with days to 50% flowering. However, grain yield had a significant and positive correlation with plant height. Path coefficient analysis indicated that plant height and early vigour had a positive direct effect on yield while days to 50% flowering and days to 50% podding had negative indirect effects on yield via days to maturity. The genotype by trait biplot graphically showed consistent trait relationships and identified TGX 2001-3FM, TGX 2001-26DM and TGX 2002-3DM as genotypes that can be used as parents in breeding programmes for yield improvement. Estimation of genetic diversity among 48 soybean lines from the International Institute for Tropical Agriculture (IITA) was conducted using 348 SNP markers. The average gene diversity and genetic distance ranged from 0.42 to 0.55 with an average of 0.47 and 0.61 to 0.87, respectively. The polymorphic information content ranged from 0.44 to 0.50 with a mean of 0.48. Genotypes TGX 2002-3DM and TGX 2002-3FM had the highest genetic distance between them indicating that they were highly diverse. The AMOVA indicated highly significant differences at F=0.001 with among individuals, among populations and within individuals contributing 45%, 28% and 26%, respectively. The 48 soybean lines were clustered in three main groups. The study indicated that genetic diversity exists among the IITA tested lines. The information obtained from the study, can be fully utilised in future soybean breeding programmes through crossing of diverse parents in order to incorporate new alleles to develop improved cultivars. In general, the study showed the existence of genotype by environment of soybean grain yield across the selected locations in southern Africa. Based on the SNP markers, the study confirmed the existence of wide genetic diversity among the soybean lines. The lines with superior performances can be used for future breeding programmes or recommended for cultivar release.