Submitted to: Phytopathology
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2005
Publication Date: 6/1/2005
Citation: Cohen, M.F., Mazzola, M. 2005. Suppression of rhizoctonia root rot by streptomyces in brassica napus seed meal amended soil. Phytopathology 95:S20.
Technical Abstract: Amendment of soil with 0.5% Brassica napus (rape)seed meal (RSM) confers systemic protection against Rhizoctonia solani AG-5 root infection of apple seedlings. The development of a R. solani suppressive state in soil amended with low-glucosinolate B. napus var. Athena RSM was prevented by steam pasteurization of the soil immediately following incorporation of the RSM. Pasteurization of RSM prior to incorporation into soil had no effect on the subsequent development of suppressiveness. These results indicate that RSM-induced disease suppression is due to the activities of resident soil microbes. Populations of streptoycetes in RSM-amended soil quickly expanded to stable levels >20-fold higher than in soil that did not receive RSM. Suppressiveness could be restored to pasteurized RSM-amended soil by adding any of several Streptomyces strains. Populations of pseudomonads peaked one week following addition of RSM to soil and declined rapidly thereafter. The most abundant protozoan in the RSM-amended soil, the amoeba-flagellate Naegleria americana, may have a role in molding the microbial community structure since its trophozoites showed a marked feeding preference for pseudomonads relative to Streptomyces. We conclude that Streptomyces are the likely agents of disease-suppressiveness in RSM-amended soil.