Variations for some quantitative traits and molecular markers in some ancestors and cultivars of soybean, and evaluation of yield increase by breeding in the southern United States

• Main Author: Ustun, Ali
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1999
• Subjects: Genetics; Plant propagation; Plant sciences
• ISBN: 059962731X; 9780599627314

Soybean breeders have made selection mostly for yield, protein and oil content, lodging, and disease and pest resistance Genetic progress in these traits might have declined in genetic variability. The objectives of this study were (1) estimate genetic progress in the southern U.S., (2) show genetic variability of agronomic traits and molecular marker diversity in soybean over time, and (3) demonstrate the genetic variability by heritabilities and Quantitative Trait Loci (QTL) in soybean populations representing different eras in soybean breeding. Ten yield trials were conducted in Tennessee with eight ancestral lines and cultivars from different eras. Soybean yield in the southern U.S. has increased 14 kg ha−1yr−1. This increase was linear which implies that there is stiff remaining variation in the southern soybean gene pool to make genetic progress for yield. Genetic diversity among eight southern and four northern cultivars was determined by microsatellite (SSR) and DNA Amplification Fingerprinting (DAF) markers. Also, data from eight F2 populations were collected. SSR and DAF marker diversities, and heritabilities for yield and oil have declined over generations in southern soybean. Markers which have QTL associations may provide very useful information to decide parents for crosses. F2:3 lines in each cross were tested in the field for agronomic traits. With the exception of Lee x Ogden cross, other southern crosses did not reveal a significant heritability for yield. Northern x southern crosses had considerably higher heritability for yield with a low population mean. Elite lines from Lee x Ogden and from recurrent selections in northern x southern crosses can increase variability for yield in the southern gene pool. One cross of southern ancestral lines and one cross of fifth generation cultivars were also evaluated for SSR marker QTL associations with agronomic traits. In the cross between ancestral lines, SSR markers Satt022, Satt180 and Satt53 were associated with yield in F2 but Satt022 was not confirmed in F2:3 lines. In the cross between fifth generation cultivars, Satt022 was associated with yield and Satt53 was associated with oil content and plant height. These results indicate that QTLs can be a reliable way to demonstrate genetic variability.