VIEW ARTICLE

Ecology and Epidemiology

Environmental Conditions Conducive to Infection of Ryegrass by Pyricularia grisea. M. A. Moss, Former graduate research assistant, Department of Plant Pathology and Weed Science, Mississippi State University, Mississippi State 39762; L. E. Trevathan, Associate professor, Department of Plant Pathology and Weed Science, Mississippi State University, Mississippi State 39762. Phytopathology 77:863-866. Accepted for publication 12 November 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-863.

Environmental conditions conducive to infection of ryegrass (Lolium multiflorum) by Pyricularia grisea were characterized and the relative susceptibility of ryegrass cultivars was determined. Infection of 3-wk-old plants of the susceptible cultivar Gulf increased exponentially with increasing inoculum densities up to 8 × 10⁵ conidia per milliliter. The youngest leaf of individual plants developed very few lesions in comparison with the more mature second, third, and fourth leaves. Maximum infection was predicted to occur on plants 4.7 wk old. The optimum temperature for infection was predicted to be 26 C. Few lesions occurred at 35 C, and none were observed at 5 C. A continual leaf-wetness period of at least 24 hr was required for maximum infection and may be the critical factor in epidemic disease development. Marshall, Sunbelt, and Tetrablend 444 cultivars developed fewer lesions than did the more susceptible cultivar Gulf.