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The Heritability of Three Parasitic Fitness Attributes of Helminthosporium maydis race T. J. P. Hill, Assistant professor, Department of Botany and Plant Pathology, Colorado State University, Fort Collins 80523—formerly research aide, Department of Plant Pathology, The Pennsylvania State University; R. R. Nelson, Evan Pugh Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 72:525-528. Accepted for publication 10 August 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-525.

Nine sets of 24 ascoprogeny were isolated from complete octads obtained from five crosses of isolates of Helminthosporium maydis race T. Conidia of the ascoprogeny were used to quantitatively inoculate RX404 Tms corn hybrid seedlings. Each experiment included four replications of inoculations with the 24 ascoprogeny isolates and the parents. Disease efficiency (DE), the average number of lesions per plant; lesion size (LS), the average lesion area; and sporulation capacity (SC), the average number of conidia produced per square millimeter of lesion was measured. The data obtained from each experiment for each parasitic fitness attribute were analyzed by a two-way analysis of variance, and genotypic and phenotypic variances were calculated. Epistasis was estimated by subtracting the progeny mean from the parental mean. Narrow-sense heritability, the ratio of the additive genetic variance to phenotypic variance, was calculated if epistasis was not significant, and broad-sense heritability, the ratio of genotypic variance to phenotypic variance, was calculated if epistasis was significant. The heritability estimates ranged from 21 to 58% for DE, 23 to 53% for SC, and 0 to 6% for LS. These results indicate that the fitness attributes of DE and SC are subject to selection. Increased parasitic fitness of DE and SC may result in a reduced effectiveness of nonspecific resistance.

Additional keywords: southern corn leaf blight, Zea mays.