Scanning electron microscopy of the infection of beans by Rhizoctonia solani Propagules

Germination, hyphal spread, and formation of infection cushions and lesions on bean hypocotyls by infective large propagules of Rhizoctonia solani were studied with the scanning electron microscope. The surface of old, but not of young, hyphae appeared typically wrinkled and shrunken. Infection cushions appeared as a network of several layers of crossed anastomosing hyphae. These features could not be observed under the light microscope. No differences in the surfaces of infective and non-infective small propagules could be observed. Non-infective propagules germinating on the hypocotyls gave rise to spreading hyphae but did not develop infection cushions.