Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2003
Publication Date: 12/3/2003
Citation: Kull, L.S., Vuong, T.D., Powers, K.S., Eskridge, K., Steadman, J.R., Hartman, G.L. 2003. Evaluation of three resistance screening methods using six sclerotinia sclerotiorum isolates and three entries of each soybean and dry bean. Plant Disease; 87:1471-1476. Interpretive Summary: A fungal disease of dry bean, soybean and other crops caused by Sclerotinia sclerotiorum can cause major limitations to production. A quick and accurate screening method is needed to facilitate the identification of resistance in host germplasm. Three screening methods and multiple isolates of the fungus were tested. For both dry beans and soybeans, all three screening methods identified isolate differences based on how much disease they caused, but each screening method did not equally identify susceptible and partially resistant cultivars. The cut stem method had the least amount of variation in the results and was concluded to be the best method to facilitate with the identification of resistance in host germplasm. The accomplishment of this work is the discovery of an inoculation technique that can be used for at least two crops to differentiate resistance. The information in this paper is useful for both commercial and public breeders and pathologists that work on resistance to the diseases caused by S. sclerotiorum.
Technical Abstract: Data from three screening methods used to identify levels of resistance to Sclerotinia sclerotiorum for soybean (Glycine max) and a dry bean (Phaseolus vulgaris) genotypes were compared by five statistical methods. Analysis of variance and mean separation tests were used to separate genotypes by resistance level and isolates by aggressiveness level. Six S. sclerotiorum isolates of known relative aggressiveness, and three soybean and three dry bean genotypes with varying levels of resistance to S. sclerotiorum were utilized. The three screening methods were mycelial plug inoculations of cotyledons, cut stems, and detached leaves. For soybeans, all three inoculation methods accurately identified isolate aggressiveness levels irrespective of cultivars, but identification of susceptible and partially resistant soybean cultivars was influenced by isolate. For a dry bean, the cotyledon and cut stem methods accurately identified isolate aggressiveness levels, but identification of susceptible and partially resistant a dry bean cultivar was influenced by isolate and inoculation method. The cut stem method had the smallest coefficient of variation, was more precise at detecting interactions, and correlated with the other two methods. The sensitivity ratio showed the cut stem method to be superior to both other methods. The cotyledon method approached the technical merit of the cut stem method for both soybean and dry beans. When considering all five statistical analyses of resistance screening methods under controlled environmental conditions, the cut stem method was superior to the cotyledon method which was superior to the detached leaf method.