VIEW ARTICLE

Genetics

Genetic Control of Two 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, Pennsylvania State University); R. R. Nelson, Evan Pugh Professor, Department of Plant Pathology, Pennsylvania State University, University Park 16802. Phytopathology 73:455-457. Accepted for publication 27 September 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-455.

Sets of 24 ascospores were isolated from crosses between seven isolates of Helminthosporium maydis race T. Conidial suspensions of ascospore cultures were used to inoculate quantitatively seedlings of two corn hybrids (RX404 and PA887 × B14) in Texas male-sterile cytoplasm. Disease efficiency (DE, the average number of lesions per plant) and sporulation capacity (SC, the average number of conidia produced per square millimeter of lesion) were measured and analyzed. The genotypic variance was calculated and used along with the progeny extreme values to estimate the number of effective factors controlling these two parasitic fitness attributes. The effective factor estimates from the 24 ascospore analyses ranged from 2.8 to 6.7 for DE and from 4.0 to 7.5 for SC. Pooled estimates ranged from 5.8 to 7.9 and from 15.8 to 25.4 for DE and SC, respectively. These results, along with the relatively high heritabilities of DE (21- 58%) and SC (23- 52%), suggest that these parasitic fitness attributes could respond to selection. The utilization of “nonspecific” resistance may provide selection pressure toward increased parasitic fitness.