Scanning Electron Microscopy of the Infection of Beans by Rhizoctonia solani Propagules

Germination, hyphal spread, and formation of infection cushionsand lesions on bean hypocotyls by infective large propagulesof Rhizoctonia solani were studied with the scanning electronmicroscope. The surface of old, but not of young, hyphae appearedtypically wrinkled and shrunken. Infection cushions appearedas 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-infectivesmall propagules could be observed. Non-infective propagulesgerminating on the hypocotyls gave rise to spreading hyphaebut did not develop infection cushions.