Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/1998
Publication Date: N/A
Citation: N/A Interpretive Summary: Only four ancestral lines account for nearly 50% of all of the genes in soybean varieties currently grown in the U.S. Because there are so few ancestors of the current U.S. varieties, many of these varieties are as closely related as half-brother and sister. This close relationship among current varieties, which are also used as parents for developing new varieties, could make future continued progress difficult in improving yield. The USDA Soybean Germplasm Collection contains more than 15,000 varieties of soybean that do not appear in the pedigrees of any current varieties, but there are two major problems in utilizing this material. There are no pedigree records to tell us how closely related these varieties are to ancestors of current U.S. varieties and all of these varieties are much lower yielding than our current varieties. Previous attempts to utilize these varieties have been successful in increasing genetic diversity but have been unsuccessful in increasing yield. By comparing varieties at the DNA level, we were able to select varieties from the USDA Soybean Germplasm Collection that were not closely related to ancestral lines. By using many of the exotic varieties in our breeding program, we were able to identify some relatively low yielding exotic varieties that could increase the yield of much higher yielding U.S. varieties. We have shown that experimental lines developed from these crosses can yield as much as and are genetically distinct from the best U.S. varieties. These released lines have yields that are sufficiently high that they will be used in varietal development programs of both public and private soybean breeders and allow them to expand the genetic diversity of the commercially used gene pool while increasing seed yield.
Technical Abstract: Only four ancestral lines account for nearly 50% of all of the genes in soybean varieties currently being grown in the U.S. Expanding the diversity of the genetic base of U.S. soybean production could have both short- and long-term positive effects on yield improvement. We have developed and released two experimental lines that can be used for that purpose. LG90-2550 is an F6 selection from LG82-8224xLG82-8195. LG82-8224 and LG82-8195 are F4 selections from the cross of PI68658xLawrence. LG90-2550 is resistant to race 7 of P. sojae and has a low level of iron chlorosis. LG90-2550 is in maturity group (MG) III with semi-determinate stems (presumably Dt2Dt2) and is comparable in yield to current MG III cultivars. LG91-7350R is an F10 reselection from LG91-7350. LG91-7350 is an F6 selection from BSR101xLG82-8379. LG82-8379 is an F4 selection from PI68508xFC04007B. LG91-7350 is heterogeneous, most notable for reaction to race 7 of P. sojae and pubescence color. LG91-7350R is high-yielding, uniform for pubescence color, and resistant to races 1, 3, 7, and 10 of P. sojae. LG91-7350R is in MG IV with indeterminate stems and is comparable in yield in current MG IV cultivars. The three exotic parental lines (FC04007B, PI68508, PI68658) are yellow-seeded, grain-type soybeans in MG II or III that have been in the USDA Soybean Germplasm Collection for more than 70 years. These introductions do not occur in the pedigrees of any released cultivars or germplasm. Research employing RAPD markers and cluster analysis to evaluate genetic diversity has shown that the introductions used in these crosses are genetically distinct from the current U.S. soybean genetic base and that diversity has been preserved after selection for high yield in the progeny.