The vast majority of genes in soybean varieties in the United States have come from only about 15 ancestors, and the genetic base is even narrower for varieties adapted to the South, says Dr. Clay Sneller, University of Arkansas soybean breeder and geneticist.
Sneller and plant pathologists Drs. John Rupe and Bob Riggs at UA-Fayetteville are principal investigators in a soybean breeding and genetics research program partly funded by the Arkansas Soybean Promotion Board (ASPB). Another ASPB funded breeding program is conducted by Drs. J. D. Widick and John Muir at Arkansas State University in Jonesboro.
The lack of diversity in the "gene pool" that soybean breeders draw from makes it difflcult to improve yield and other important traits of soybeans, Sneller said.
One reason for the lack of diversity is that yield potential is usually lower in breeding lines that are genetically different from current adapted varieties. In their zeal to increase yields, breeders usually cross parent lines that have high yield and are closely related.
"Our objective is to combine good yield potential with genetic diversity," said Sneller. "To do this we must assess both the yield potential and diversity of potential parents."
The objective is to combine good yield potential with genetic diversity.
Accurate assessment of genetic diversity is now feasible using DNA fingerprinting tech niques that have been adapted to soybeans in the last seven years. Jay Miles conducts the finger printing in the UA soybean genetics laboratory, and information is also obtained from Michigan State University.
"We have identified several new parents that appear to have adequate yield potential and that are quite diverse from our south ern cultivars," Sneller said.
Crosses have been made between these parents and southern varieties. Crosses have also been made between south ern varieties and northern varieties that appear diverse and to have high yield potential in the South. The progeny from these crosses will be tested for yield potential in 1996.
The germplasm resulting from these crosses will be released for use by other breeders. 'We won't sit on lines with high yield potential and genetic diversity, because Arkansas farmers will benefit the most from their use by all soybean breeders," Sneller said.
Potential New Variety
The breeding team's shorterterm efforts to develop improved varieties may yield results in a promising line that underwent its final year of field testing in 1995. Data are being analyzed this fall to determine if the line has the yield potential and disease resistance required for release as a new UofA variety.
Other areas of emphasis in the UofA breeding program include:
UofA researchers have identified reducedSfixatiori of nitrogen from the air as a key factor in seed yield reduction due to drought. Genes that allow plants to maintain a higher level of nitrogen fixation during drought might be useful for improving drought tolerance.
Widick and Muir, at ASU, screen potential soybean parent conditions such as chloride, high salt and high or low pH.
They are identifying problem fields in the state and will use a genetic "shotgun approach" of planting as many different geno types of soybean in each field as they can to try to identify those that are best adapted.
Widick, a soybean breeder, and Muir, a plant nutritionist, screen all entries in the Arkansas Commercial Cultivar Test and the Southern Regional Soybean Uniform Tests for chloride reaction. The results are used by farmers to select varieties for soils with high chlofide and to assist breeders in developing chloride tolerant varieties.