VIEW ARTICLE

Influence of Exogenous Nutrition on Virulence of Rhizoctonia solani. A. R. Weinhold, Associate Professor, Department of Plant Pathology, University of California, Berkeley 94720; R. L. Dodman(2), and Tully Bowman(3). (2)Department of Plant Pathology, University of California, Berkeley 94720, Present address: Queensland Wheat Research Institute, Toowoomba, Queensland, Australia; (3)Staff Research Associate, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 62:278-281. Accepted for publication 20 September 1971. DOI: 10.1094/Phyto-62-278.

Virulence of Rhizoctonia solani is markedly influenced by the quantity of available nutrients. Sources of nutrients and the capacity of the pathogen to utilize these materials are important considerations in understanding disease development in nature. Mycelium growing from inoculum deficient in nitrogen rapidly absorbed nitrogen-containing compounds from the external environment and utilized them for pathogenic activities. The potential importance of soil as a source of nutrients for R. solani was shown by the fact that in the presence of soil, disease severity in cotton resulting from inoculation with nitrogen-deficient mycelium was increased. The addition of nitrogen to the soil resulted in a further increase in lesion development. At all levels of inoculum nutrition, seed inoculation resulted in greater disease severity than did hypocotyl inoculation. This supports the suggestion that seed exudates are an important source of nutrients available to soil-borne pathogens in nature. Seedling survival and lesion area on survivors were related to inoculum nutrition and initial distance between inoculum and seed. As this distance was increased, higher levels of inoculum nutrition were required for severe seedling damage. This study showed that the nutrients available to R. solani include those present in the propagule, the soil solutions, and the host exudates.