A disease assay for Rhizoctonia solani on potato (Solanum tuberosum)

Abstract

Rhizoctonia solani is an important soilborne pathogen of potato, causing black scurf on tubers and shoot/stolon canker on young plants. These diseases reduce the quality of fresh and seed potatoes and may harm crop establishment. A pathogenicity test has been developed for the study of biological suppression of diseases caused by R. solani. Disease expression from two R. solani isolates was assessed in potato plants grown from tissuecultured plantlets or from minitubers. The isolates were cultured in two media, bran+water or barley grain+V8 juice®which were compared as inoculants of potting mix at several standardised rates. The proportions of diseased stolons and necrotic shoots were determined after 7 weeks growth in a greenhouse. Significantly different levels of disease incidence were found between the isolates, between inoculum concentrations for one isolate, and (only with minitubers) between inoculum media. Rates of inoculum that produced disease levels suitable for use in biocontrol assays were determined.