An Agricultural Research Service (ARS)-led team of scientists has challenged the widely held assumption that two “genetic bottlenecks” have drastically reduced genetic variability in soybean varieties grown in farmers’ fields.
The first bottleneck was said to be plant breeders’ tendency to use only a few parent soybeans from Asia, called “landraces,” to build the genetic base of U.S. soybean in the 1930s and 1940s. The second bottleneck was breeders’ use of a small group of elite varieties as parents in each succeeding round of breeding during the past 60 years.
However, in a November 2006 paper published in the Proceedings of the National Academy of Sciences, a team led by ARS geneticists Perry Cregan and David Hyten argues that this isn’t the case, based on their analysis of alternate gene forms, called alleles, from four major soybean groups. These included 26 samples of wild soybean, Glycine soja; 52 Asian landraces; 17 landrace “founders” used to establish America’s soy crop; and 25 elite cultivars.
According to Cregan and Hyten, with the ARS Soybean Genomics and Improvement Laboratory at Beltsville, Md., their results indicate only a small proportion of the landraces’ diversity was lost following their introduction from Asia and subsequent years of intensive plant breeding. Rather, the limited diversity stems from the inherently low diversity in wild soybean and further loss related to its domestication thousands of years ago in Asia.
Cregan and Hyten agree that ensuring genetic variability in soybean is critical to protecting the crop from new disease and insect pests. However, they emphasize the importance of anticipating an exotic pest’s or pathogen’s eventual U.S. arrival, and conducting searches for resistance genes in the ARS Soybean Germplasm Collection at Urbana, Ill. Such genes could then be bred into America’s elite well before an outbreak of that pest or pathogen. Cregan and Hyten’s collaborators include scientists from two other ARS labs, the University of Maryland, and the University of Nebraska.