2012 Annual Report
The Drought Tolerance project seeks to unlock the rich store of drought tolerance genes that exist in the USDA’s preserve of soybean germplasm. This reservoir of exotic diversity, although collected by scientists, was produced originally by over 3000 years of ‘on-farm breeding’ in Asia, in which farmers selected and adapted the soybean for human use under a range of climate conditions. Special genes for drought tolerance, bred into soybean so long ago by these ancient farmers, are key to coping with the problem of drought in the USA today. U.S. varieties do not presently contain these special drought genes from Asia. The central theme of our drought tolerance work is that we can ‘turn the tables’ on drought in the USA by putting the world’s genetic resources in soybean to work on U.S. farms. To that end, the United Soybean Board's drought tolerance project coordinates the research activities of 8 scientists and 7 research institutions in the Midwest and South, aimed at transferring drought genes from exotic Asian material into adapted genetic materials. A major factor determining success in the genetic improvement of drought tolerance is the physiological processes that give rise to drought tolerance.
A key physiological process is the genetic response of soybean leaves to drying air and soil conditions. Exotic soybeans have been identified that are ‘slower to wilt’ under drought stress than normal soybean varieties. The slow-wilting types, normal controls, and selected wild soybean accession from dry regions of China, were compared for their stomatal response to drying air in a first series of experiments. These same genotypes were subsequently compared for response to drying soil. All of these experiments were conducted in growth chambers. Slow wilting soybean types varied among themselves and in comparison to normal controls with respect to closing of stomata, when subjected to incrementally drier air. Some slow-wilting types clearly closed their stomata sooner than controls. Stomatal response to drying soil was relatively similar for all soybean types which were tested. In contrast, the wild soybean accessions did not differ in stomatal response to drying air, but differed in stomatal response to drying soil. These results have been confirmed and journal manuscripts have been submitted. Drought tolerance traits from the wild and domesticated soybean might be combined through breeding to produce the most desirable breeding stock carrying both forms of drought tolerance. The relation of these results to aquaporins is being investigated. Preliminary quantitative trait loci (QTL) analysis reveals a major QTL for aquaporin activity derived from exotic soybean PI 416937. Genomic analyses are underway to identify candidate genes which may control aquaporin activity. Advanced lines were evaluated for sustained nitrogen fixation activity under drought.