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Cytology and Histology

Infection Cushion Formation on Rice Sheaths by Rhizoctonia solani. D. S. Marshall, 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 Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; M. C. Rush, professor, Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Experiment Station, Baton Rouge 70803. Phytopathology 70:947-950. Accepted for publication 20 March 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-947.

Replicas were made of outer sheath surfaces of rice cultivars which were resistant or susceptible to rice sheath blight caused by Rhizoctonia solani. Lobate appressoria and infection cushions, which are infection structures formed by the fungus on sheath surfaces, were not formed on the replicas. When sheath tissue from rice cultivars was placed under collodion membranes, both types of infection structures formed on the membranes over tissue from susceptible cultivars. Cultivars varying in levels of resistance to sheath blight were grown under identical greenhouse conditions. Abundant wax deposits were observed on the outer sheaths of resistant cultivars. No wax deposits were observed on the outer sheaths of susceptible cultivars. Cultivars intermediate in resistance had varying amounts of wax deposits on their outer sheaths. Removal of wax deposits from resistant cultivars with chloroform, followed by inoculation with R. solani, resulted in a susceptible reaction. An exogenous supply of glucose and 3-O-methylglucose reduced lesion development in rice seedlings. The apparent mode of action of 3-O-methylglucose was to inhibit infection cushion formation.