VIEW ARTICLE

Ecology and Epidemiology

Effect of Host Genotype on Estimating Relative Parasitic Fitness Among Populations of Helminthosporium carbonum Race 3. L. V. Gregory, Research assistant, Department of Plant Pathology, Pennsylvania State University, University Park 16802; J. E. Ayers(2), and R. R. Nelson(3). (2)(3)Professor, and Evan Pugh professor, respectively, Department of Plant Pathology, Pennsylvania State University, University Park 16802. Phytopathology 74:1024-1026. Accepted for publication 27 March 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1024.

Changes in the relative parasitic fitness of populations of Helminthosporium carbonum (= Cochliobolus carbonum) race 3 were studied using four populations of the fungus. Three populations, 10 isolates each, were collected in Pennsylvania in 1970, 1974, and 1979. The fourth population also consisted of 10 isolates and was collected from Illinois in 1979. Ten cultivars of greenhouse-grown corn (Zea mays) were inoculated at the three- to four-leaf stage with these 40 isolates. After 15 days, lesion length as a measure of parasitic fitness was determined. From the interaction of isolates and cultivars, it was evident that parasitic fitness was specific and that statistically significant differences among populations were dependent on the cultivar used to evaluate parasitic fitness. Variances of mean lesion length of the 1970 Pennsylvania and the Illinois populations were generally lower than the variances of the 1974 and 1979 Pennsylvania populations although there was some dependence on cultivar. The data suggest that choice of cultivar can be critical to the evaluation of parasitic fitness.