VIEW ARTICLE

Physiology and Biochemistry

Expression of Disease Reaction Types in Soybean Callus from Resistant and Susceptible Plants. M. J. Holliday, Graduate student, Department of Botany, University of Maryland, College Park, 20742; W. L. Klarman, professor, Department of Botany, University of Maryland, College Park, 20742. Phytopathology 69:576-578. Accepted for publication 5 December 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-576.

Conditions influencing expression of disease reaction types were examined in calluses derived from soybean plants resistant (cultivar Cutler 71) or susceptible (cultivar Cutler) to race 1 of Phytophthora megasperma var. sojae (Pms). Cutler 71 calluses were colonized less than those of Cutler when both were grown on medium containing 6 or 10 mg of 2,4-D/L and incubated at 16 or 20 C prior to and following inoculation with Pms zoospores. Differences between colonization rates of Cutler and Cutler 71 calluses were greater in callus sections 5 mm thick than in thicker or thinner sections. Differences in colonization rates remained high with inoculum doses varying from 50 to 1,000 zoospores per callus section. Sections of Cutler and Cutler 71 calluses 5 mm thick were colonized equally by race 3 of Pms which is pathogenic to plants of both cultivars. No combinations of incubation temperatures, 2,4-D concentrations, sizes of calluses, or numbers of zoospores used for inoculum resulted in Cutler 71 calluses with the nearly absolute resistance to race 1 of Pms found in whole plants of that cultivar.