Evaluation of Resistance Screening Methods for Sclerotinia Stem Rot of Soybean and Dry Bean

Three methods to identify levels of resistance to Sclerotinia sclerotiorum in soybean (Glycine max) and dry bean (Phaseolus vulgaris) were compared using multiple data analyses. The three methods were mycelial plug inoculations of cotyledons, cut stems, and detached leaves. Six S. sclerotiorum isolates of known relative aggressiveness were inoculated on each of three soybean and dry bean cultivars with varied response to S. sclerotiorum. For soybean, all three inoculation methods accurately identified isolate aggressiveness irrespective of cultivar, but identification of susceptible and partially resistant soybean cultivars was influenced by isolate. For dry bean, the cotyledon and cut stem methods accurately identified isolate aggressiveness, but identification of susceptible and partially resistant dry bean cultivars was influenced by isolate and inoculation method. The cut stem method had the smallest coefficient of variation and was more precise for detecting interactions. When considering root mean square residual error combined over species and experiments, coefficient of variation based on residual error, significance of isolate-by-cultivar interaction from ANOVA, rank correlation between pairs of methods, and sensitivity ratio for the three resistance screening methods under controlled environmental conditions, the cut stem method was statistically better than the cotyledon and detached leaf methods for evaluating resistance in soybean and dry bean cultivars.