|St. Martin, Steve|
Submitted to: Proceedings of the International Sclerotinia Workshop
Publication Type: Proceedings
Publication Acceptance Date: 1/22/2003
Publication Date: 1/20/2003
Citation: Diers, B., Hartman, G.L., Grau, C., Dorrance, A., St. Martin, S., Wang, D., Nelson, B. 2003. Characterization of soybean genotypes with partial resistance to sclerotinia stem rot. Proceedings of the International Sclerotinia Workshop; 2003.
Technical Abstract: Progress was made in three areas of research. The goal of the first area is to improve the sclerotinia stem rot resistance of elite soybean germplasm. This is being done through the mapping of quantitative trait loci (QTL) for resistance from plant introductions. The mapping is being done in three populations developed from crosses between partially resistant soybean plant introductions and partially resistant or susceptible varieties. These populations are being tested for resistance and with genetic markers. Population 1 was developed form crossing NKS 19-90 with PI 153282. Lines from the population were evaluated for resistance during the summer of 2002 in three field locations. There was a modest level of disease at two locations and the lines were rated for disease severity. Lines from population 2 (Merit x PI194639) were grown in the greenhouse during the summer of 2002. Genetic marker testing of both population 1 and 2 has been initiated. Plants in population 3 (Kottman(2) x PI391589A) were grown during the summer of 2002 and are now being increased in Chile this winter. In the second area of research, we are addressing whether resistant and susceptible soybean lines differ in anatomical and biochemical traits. To test this, an isolate of S. Sclerotiorum transformed with the green fluorescent protein (GFP) and a second nontransformed isolate was used to challenge soybean plants with petiole inoculation technique (PIT). Both isolate was equally aggressive and challenged and nonchallenged plants were examined using a fluorescence stereo microscope. The transformed isolate fluoresced green but so did soybean tissue. Petioles of the partially resistant variety NKS 19-90 and the susceptible variety M0301 were inoculated with S. Sclerotiorum and examined at various times post inoculation to study mycelial development. Improvements have been made to the techniques to obtain good staining of the mycelium for viewing and for quantifying observations with light microscopy. No differences have been observed between cultivars in the first 48 hours after inoculation, but this work is continuing and observations at additional times are being made. In the third area of research, methods used in the PIT were evaluated to determine if this method can be improved. Alternative sources of culture medium were evaluated that promote greater synthesis of oxalic acid and endopolygalacturonase, both accepted as pathogenicity factors produced by S. Sclerotiorum. Rate of lesion expansion, total lesion length, rate of plant death, plant survival and pathogen reproduction were not affected by composition of media used to produce inoculum of S. Sclerotiorum.