| Soybean seeds are a unique dietary source of isoflavones, which have been shown to reduce the risk of several major diseases in humans. Therefore, developing soybean seeds with desirable isoflavone content would be beneficial to the growers, and food and health industries. Isoflavone concentrations are environmentally sensitive and their analyses can be very expensive for most plant breeding programs. Furthermore, little is known about the effects of altered isoflavone content in the seed on important agronomic and seed quality traits. The objectives of this study were: (1) to evaluate the agronomic performance of three isoflavone phenotypic classes ('high', 'intermediate', and 'low'), (2) to map quantitative trait loci (QTL) associated with individual and total isoflavone content in soybean seeds, and (3) to identify novel QTL associated with agronomic and seed quality traits. Results indicated that 'high' isoflavone recombinant inbred lines (RILs) produced higher seed yield, matured later, were taller, lodged more, and had lower protein content than the 'low' RILs. Oil content and seed quality were significantly different among three isoflavone classes but no consistent pattern was observed. Seed weight was not significantly different among the classes. Data for QTL analysis was collected over two locations in Southern Ontario in 2001, using a RIL population derived from the cross AC756 x RCAT Angora. QTL for individual and total isoflavone content were identified on five linkage groups (LGs A1, H, J, K, and M). The R 2 ranged from 3.4% (P = 0.0099) to 10.5% ( P < 0.0001) for individual markers. Novel QTL with large effects were identified for maturity, lodging, oil and protein content, and seed quality on LGs D1b, E, F, J, N, and O. Regions associated with isoflavone content, and agronomic and seed quality traits mapped to common areas of the genetic linkage map (LGs M, J, and K). This report shows a genetic association between isoflavone content (individual and total) and agronomic traits, and between glycitein and protein. Marker-assisted selection could be a more efficient and less expensive method for developing soybean with desirable isoflavone content in the seeds and superior agronomic traits. |
