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Ecology and Epidemiology

Ecological Races of Helminthosporium maydis Race T. J. P. Hill, Research Aide, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; R. R. Nelson, Evan Pugh Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 66:873-876. Accepted for publication 20 January 1976. DOI: 10.1094/Phyto-66-873.

A cool-environment population and a warm-environment population of Helminthosporium maydis race T were evaluated for virulence, infection efficiency, and sporulation efficiency under cool and warm temperature regimes. Each population was superior to the other in an environmental regime comparable to its native habitat. Infection and sporulation efficiencies were greater for the cool-environment population under the cool regime and greater for the warm-environment population under the warm regime. Infection and sporulation efficiencies of the two populations were similar after continued exposure to a cool or a warm temperature regime, apparently due to selection for subpopulations that were better able to persist under those regimes.