Effects of Organic Matter Decomposition Level and Cellulose Amendment on the Inoculum Potential ofRhizoctonia solaniin Hardwood Bark Media

Abstract

Container media amended with fresh hardwood bark (.apprx. 45% cellulose, w/w) were conducive to Rhizoctonia damping-off of radish. Those amended with hardwood bark compost were suppressive. Significantly higher cellulase activity was present in the fresh bark medium colonized by R. solani than in the bark compost medium. The population of R. solani increased in the fresh bark compost medium. Addition of low levels of cellulose (5%, w/w) to the bark compost medium decreased damping-off. High levels of cellulose (20%, w/w) established high cellulase levels in the Rizoctonia-infested bark compost media, increased the population of R. solani, and negated suppression. Even in the presence of a suppressive microflora, the high cellulose amendment increased conduciveness. We conclude that high cellulose levels increase the inoculum potential of R. solani, resulting in increased damping-off severity.