VIEW ARTICLE

Colonization of Stem Segments and Chitin Particles by Rhizoctonia solani in Soil. B. Sneh, Assistant, Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel; J. Katan(2), and Y. Henis(3). (2)(3)Lecturer, and Associate Professor, respectively, Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel. Phytopathology 62:852-857. Accepted for publication 31 January 1972. DOI: 10.1094/Phyto-62-852.

Incubation of bean (Phaseolus vulgaris ‘Brittle Wax’) stem segments and chitin particles in Rhizoctonia-free soil, resulted in a significant suppression of subsequent colonization by Rhizoctonia solani. Autoclaving, extracting the previously incubated stem segments and chitin particles with ethanol, or sterilizing the chitin particles with gamma irradiation allowed them to be colonized to nearly the same level as the nonincubated segments and particles. The ethanol extracts of incubated stem segments and chitin particles contained thermostable substances inhibitory to R. solani. The colonization of bean stem segments by R. solani was not correlated with content of soluble nutrients. Suppression of colonization of R. solani observed with incubated stem segments and chitin particles is ascribed either to competition for degradation products between the established microflora in these substrate units and R. solani or to the production of unknown antifungal substances, or both. Rhizoctonia solani did not survive after incubation for 1 month in a wet, natural sandy-loam soil, but did survive in sterile soil kept aseptically under the same conditions. The decrease observed in colonization of chitin particles colonized with R. solani, when incubated in chitin-amended soil, did not differ significantly from that in particles incubated in nonamended soil. A significantly greater decrease in colonization of chitin particles by R. solani was observed when the particles were incubated in sterile soil infested with antibiotic-producing microorganisms than in soil infested with nonantibiotic-producing microorganisms. Survival of R. solani in plant debris and incidence of damping-off of onion seedlings caused by this fungus in naturally infested soil were much higher after an incubation period of 360 days in air-dried soil than in soil kept at 50% of its moisture-holding capacity.