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Mode of Inhibition of Rhizoctonia solani in Chitin-Amended 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 61:1113-1117. Accepted for publication 22 April 1971. DOI: 10.1094/Phyto-61-1113.

Saprophytic growth and pathogenicity of Rhizoctonia solani were reduced in natural, chitin-amended soil during 22 and 42 days of incubation, respectively. Increasing chitin concentrations from 500 ppm to 8,000 ppm resulted in increased inhibition of saprophytic growth during the first 3 days, but did not affect maximum inhibition. Inhibition of saprophytic growth could not be detected in sterilized soil amended with chitin, or in amended soil which was autoclaved or gamma-irradiated after a 14-day incubation period. Addition of lignin had no significant effect on pathogenicity of R. solani, nor did it increase the inhibitory effect of chitin. Both chitin and lignin alone and the two in combination had no significant effect on disease severity of bean caused by Fusarium solani f. sp. phaseoli. No parasitism or lysis of R. solani hyphae by soil organisms was observed in chitin-amended soil. Addition of glucose or ammonium nitrate to chitin-amended soil did not reduce the inhibition of saprophytic growth of R. solani. Volatile substances produced in chitin-amended soil inhibited saprophytic growth of R. solani only during the first 12 days of incubation. The fungus was not inhibited in sucrose-amended soil in which CO₂ was produced in greater quantities than in chitin-amended soil. Inhibition was not correlated with competition between R. solani and the soil microflora for available nutrients, but seemed to result from the effect of inhibitory compounds of an unknown nature produced by the soil microflora during chitin decomposition.