2009 Annual Report
Enhancing Sclerotinia resistance in soybean: Management strategies for Sclerotinia stem rot or white mold of soybean have limitations. Crop culture modifications often compromise high yield, fungicides add to production costs, and resistance found to date is partial, multigenic, and complex. We are working toward increasing the level of resistance to Sclerotinia sclerotiorum in soybean cultivars and to develop and evaluate improved disease control and resistance options for soybean producers. Our first goal is to combine quantitative trait loci (QTL) that were previously mapped and identified with the resistance phenotype into single breeding lines. The QTL come from different sources and represent 8 QTL on 7 different linkage groups. Nineteen soybean lines with resistance alleles at multiple QTL were identified as having a level of resistance equal to or better than the resistant check NKS19-90 and the parental QTL lines from three populations. The 19 lines were evaluated in yield tests during 2008. Initial yield test results indicate that lines with improved resistance and similar yield will be recovered. They will be useful as parents to develop higher yielding soybean lines with improved resistance to Sclerotinia stem rot. Yield tests were planted again for 2009 in four tests at three locations. The combined analysis and results will be completed after 2009 harvest. The second goal is to determine if a novel antifungal synthetic peptide expressed in soybean will confer resistance to S. sclerotiorum. Some reports indicated broader antimicrobial activity of such a peptide, including other fungal and some bacterial pathogens. We developed transformed plants with a codon-optimized gene-expression cassette for the antifungal peptide that contains the barley alpha-amylase signal sequence to export the peptide to the apoplast. We conducted the DLT on T2 populations from seven independent transformation events. Results indicated no significant difference between the plants with the lytic peptide and those without the inserted gene expression cassette. No further studies are planned with the lytic peptide. Because of the cost of commercializing genetically modified organisms, our conclusion is that the effect of the antifungal peptide is not significant enough to warrant further development effort. The National Sclerotinia Initiative contributes to the goals of ARS National Program 303 – Plant Diseases.