Response of Susceptible and Moderately Resistant Pea Genotypes to Interaction Between Rhizoctonia solani and Three Other Stem and Root Rot Pathogens. M. A. Shehata, Associate Scientist, Department of Horticultural Science and Landscape Architecture, University of Minnesota, St. Paul 55108. F. L. Pfleger, Associate Professor, Department of Plant Pathology, and D. W. Davis, Professor, Department of Horticultural Science and Landscape Architecture, University of Minnesota, St. Paul 55108. Plant Dis. 67:1146-1148. Accepted for publication 9 May 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1146.

Susceptible and moderately resistant peas (Little Marvel, Dark Skin Perfection, Minnesota 494-A11, and PI 257593) grown in the greenhouse in pasteurized soil beds were inoculated with Rhizoctonia solani AG4, Fusarium solani f. sp. pisi, Pythium ultimum, and Aphanomyces euteiches separately and in combinations. These combinations were R. solani plus F. solani f. sp. pisi, R. solani plus P. ultimum, R. solani plus A. euteiches, and the four-pathogen combination. Stem rot severity varied with the pathogen used in the inoculation process, either alone or in combination, as well as with cultivar. Severe stem and root rot developed when Little Marvel, a susceptible genotype, was inoculated with F. solani f. sp. pisi alone or in combination with R. solani or when all pathogens were combined by sequential inoculation. PI 257593, however, which is moderately resistant to either R. solani or F. solani f. sp. pisi, failed to maintain stem and root rot resistance when inoculated with either R. solani plus F. solani f. sp. pisi or with the four-pathogen combination. A similar relationship was found between R. solani and F. solani f. sp. pisi on Minnesota 494-A11, which is moderately resistant to F. solani f. sp. pisi, as reflected by root rot and plant mortality.