VIEW ARTICLE

Cytology and Histology

Preinfectional Interactions Between Helminthosporium oryzae and Resistant and Susceptible Rice Plants. F. C. Hau, Former graduate research assistant, Department of Plant Pathology and Crop Physiology, Louisiana State University, Agricultural Experiment Station, Baton Rouge 70803, Present address of senior author: Department of Plant Pathology, North Carolina State University, Raleigh 27650; M. C. Rush, professor, Department of Plant Pathology and Crop Physiology, Louisiana State University, Agricultural Experiment Station, Baton Rouge 70803. Phytopathology 72:285-292. Accepted for publication 2 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-285.

Comparisons were made of the prepenetration activities of Helminthosporium oryzae on plants of one susceptible, one intermediate, and two resistant rice cultivars. The percent germination of conidia on leaf surfaces was not significantly different between susceptible and resistant cultivars. On resistant plants, germ tube elongation was markedly increased. On susceptible plants, germ tubes were short, appressoria were produced early, and the hyphal mass per conidium was higher. Appressoria were mainly concentrated on bulliform cells and at junctures between epidermal cells. On polystyrene leaf surface replicas, appressoria formed equally well over all the cell types and were located mainly at cell junctures. Scanning electron microscopy showed that conidia, hyphae, and appressoria of H. oryzae were held in close contact with leaf surfaces by amorphous secreted sheathlike substances that adhered to the leaf surface, masked the wax crystals, spread some distance (5–15 μm) from the hyphae, and left imprints on leaf surfaces and their polystyrene replicas after the hyphae and the sheaths were removed.