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Correlations Between Cytologically Detected Plant-Fungal Interactions and Pathogenicity of Magnaporthe grisea Toward Weeping Lovegrass. Mich?le C. Heath, Department of Botany, University of Toronto, 25 Willcocks St., Toronto, Ont. M55 3B2, Canada; Barbara Valent, Richard J. Howard, and Forrest G. Chumley. E.I. du Pont de Nemours and Co., Inc., Central Research and Development Department, P.O. Box 80402, Wilmington, DE 19880-0402. Phytopathology 80:1382-1386. Accepted for publication 31 May 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1382.

Genetic analysis previously demonstrated that two strains of the ascomycetous plant pathogen, Magnaporthe grisea, differ in a single gene controlling pathogenicity to weeping lovegrass. This study was undertaken to determine the feasibility of identifying a microscopic feature that segregates with the gene for pathogenicity to weeping lovegrass. Cytological results are reported for weeping lovegrass inoculated with the parental strains and progeny from two tetrads obtained from crossing these strains. Many features observed at infection sites of the nonpathogenic parent clearly were not correlated with host specificity because they were observed at some infection sites of both pathogenic and nonpathogenic progeny. The identification of a strain as pathogenic or nonpathogenic to weeping lovegrass appeared to depend on whether brown cells developed around the margins of developing colonies. Because the fungus was never seen to grow beyond these brown cells, the ability to induce this plant response may play a role in determining host species specificity. Analysis of a statistically significant number of progeny will be required to determine whether this cytological feature cosegregates with the gene for host specificity.

Additional keywords: Pyricularia, resistance determinants, rice blast fungus.