Genetic Characterization and Estimation of Genotype by Environment Interaction of Ethiopian Sesame (Sesamum Indicum L.) Germplasm
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Date
2021-07-02
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Addis Ababa University
Abstract
Sesame is one of the major oil crops that has great economic importance for the country. In Ethiopia, sesame is among the foremost important oil crops both in terms of area coverage and total national annual production. However the crop suffers from low productivity due to biotic and abiotic stresses. Therefore, the present study conducted in different sets to generate information that can be used to design the future breeding program of sesame in the country. The first set of experiments was to study the morphological and molecular genetic diversity of the sesame germplasm collected from Ethiopia and other countries (Asian and other African countries). The same genotypes planted at three locations for phenotyping and genotyping using the two high throughput diversity array technology (DArT) markers (silicoDArT and SNP). Further to understand the impact of different putative genes Genome-wide association study of yield-related traits using 2997 SNPs in two environments was performed. The second set of experiments was conducted in 19 environments to assess the performance and stability of sesame varieties, and to characterize sesame growing environments in Ethiopia. Based on morphological characterization, genotypes showed wide variability for most morphological traits, except for plant growth type, leaf glands, anther filament color, and anther connective tip gland. High heritability combined with high genetic advance was recorded for plant height, primary branch, days to flower initiation, days to 50% flowering, pod bearing zone, seed yield per plant, and bacterial blight reaction indicating the potential of improving the population through a direct selection for these traits. Grain yield showed a significant and positive genotypic correlation with plant height, the number of capsules per plant, and pod bearing zone, the magnitudes of the positive genetic correlation suggest that the selection by those characters produces a significant increase in grain yield. Genetic divergence using Mahalanobis D2 statistics was computed, and the genotype lines were grouped into six different clusters. Clustering was not associated with the geographical distribution; instead, genotypes were grouped mainly based on morphological differences. The maximum inter-cluster distance was observed between clusters IV and VI (D2 =342.56, followed by clusters I, and VI (D2 =217.9783). Maximum genetic recombination and variation in the subsequent generation are expected from crosses that involve parents from the clusters characterized by
maximum distances. The genetic diversity analysis showed that the average nucleotide diversity of the panel was 0.14. Considering the genotypes based on their geographical origin, Africa collections (0.21) as a whole without Ethiopian collection was more diverse than Asia and when further portioned Africa, North Africa (0.23) collection was more diverse than others, but at the continent level, Asia (0.17) was more diverse than Africa (0.14). The genetic distance among the sesame populations ranged from 0.015 to 0.394, with an average of 0.165. The structure analysis divided the panel into four hypothetical ancestral populations and 21 genotypes were clustered as an admixture. Under Genome-wide association study (GWAS) a total of 21 significant SNPs with 7 yield-related traits in two environments were identified and, these explaining the phenotypic variation ranged from 7.02 (DF) to 16.11% (CAPL), with an average of 9.76%, suggesting a moderate contribution to the traits. All significant loci found in LG 2, 6, and 11 associated with capsule length except one associated with the physiological period. The significant loci found in LG 3, 7, and 8 associated with a physiological period (Days to flower initiation, Days to 50% flowering, and Days to physiological maturity) except one associated with capsule length. Dissecting genetic control of flowering time and maturity is importance to foster sesame breeding and to develop new varieties able to adapt to changing climatic conditions. Indeed, flowering time and maturity strongly affect yield and plant adaptation ability. Since several favorable alleles detected in this study have not yet been intensively selected, our GWAS results will assist in incorporating further useful alleles into the elite sesame germplasm for a seed yield increase in the future. Based on the genotype x environment interaction study the test locations were divided into six groups. Humera, Banat, and Tach Armacho were highly discriminating and representative in the first, the second, and the third group respectively, and were identified as a core test site in that group. While Alemaya, Worer, and Mender67 were identified as the only test site in groups four, five, and six. The core testing sites identified would be used to facilitate the identification of superior sesame varieties and to reduce testing costs in the country. Environment Tach Armacho in 2017/18 and 2018/19 were close to the ideal environment. The GGE biplot analysis identified genotype G2 (setit-1) as the “ideal” genotype and among the highest mean seed yield. Setit-1 considered the most stable across variable environments.
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Keywords
AMMI, DArTseq, Genetic Diversity, GGE Biplot, GWAS, Ideal Genotype, Population Structure, Significant Loci