Soybean improvement of seed traits and resistance to bud blight via molecular markers and classical methods
Fasoula, Vasilia Apostolos
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Three independent, but related studies were conducted to further the objective of improving soybean seed traits and resistance to tobacco ringspot virus. The objective of the first study was to identify and map the genes for bud blight caused by tobacco ringspot virus. Two populations derived from the cross of Young x PI416937 were evaluated. In the field, the plots were naturally infected with tobacco ringspot virus and were visually scored. RFLP and SSR markers were used to map the gene for bud blight. Composite interval mapping identified a major QTL for bud blight resistance between the RFLP markers K644_1 and A069_b. The major QTL was also linked to the Satt510 marker. The objective of the second study was to utilize an independent F2-derived soybean population of PI97100 x Coker 237 to confirm previously reported RFLP markers associated with seed protein, seed oil, and seed weight, mapped in an F2-derived population created from the same parents. Single-factor analysis of variance was used to confirm the RFLP loci based on the mean phenotypic data across three different environments. Two out of four previously reported QTL for seed protein, two out of three QTL for seed oil content, and one out of three QTL for seed weight were confirmed in the independent population. The objective of the third study was to investigate the presence of genetic variation for seed composition traits within three elite soybean cultivars by honeycomb selection. Divergent honeycomb selection for seed protein and oil within each cultivar was performed using a replicated-3 honeycomb design. The selected plants were evaluated in replicated row-plot experiments for three years. Honeycomb selection was successful in discovering a significant amount of within-cultivar genetic variation for seed protein and oil. Across the three cultivars, the magnitude of within-cultivar variation averaged 5% (19 g/kg) for protein and 6% (12 g/kg) for oil content. The magnitude of within-cultivar variation for fatty acid content ranged from 6 to 29 g/kg across the three cultivars.