Components of Rate-Reducing Resistance in Seedlings of Four Wheat Cultivars and Parasitic Fitness in Six Isolates ofErysiphe graminisf. sp.tritici

Abstract

Sporulation capacity and infection efficiency of 6 isolates of E. graminis f. sp. tritici collected in central Pennsylvania [USA] were measured on winter wheat cultivars Blueboy, Redcoat and Knox. Only sporulation capacity was measured on a 4th cultivar, Vermillion. Sporulation capacity was measured as the cumulative number of conidia samples from individual colonies on primary leaves at 24 h intervals and was estimated by the parameter Xm in the logistic equation by using a nonlinear regression routine. Differential interactions were found between isolates and cultivars where the ranking of isolates changed by cultivar. Infection efficiency was determined by counting the number of conidia out of groups of 10 that had formed elongating secondary hyphae 36-48 h after inoculation. Two-way analysis of variance identified the significant isolate by cultivar interactions for infection efficiency. The change in ranking and the significant statistical interaction in the analysis of variance of isolates by cultivars with respect to sporulation capacity and infection efficiency demonstrates genetic variability for these traits in wheat and E. graminis and indicates the possibility for erosion of slow mildewing resistance.