Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/24/2002
Publication Date: 10/1/2002
Citation: MAZZOLA,M., GU,Y. WHEAT GENOTYPE-SPECIFIC INDUCTION OF SOIL MICROBIAL COMMUNITIES SUPPRESSIVE TO DISEASE INCITED BY RHIZOCTONIA SOLANI AG 5 AND AG 8. PHYTOPATHOLOGY. 2002. v. 92. p. 1300-1307. Interpretive Summary: Soil ecosystems possess a wealth of biological resources that can be harnessed for use in control of plant diseases. Soils that naturally have low incidence of disease are commonly referred to as suppressive soils. Studies have been conducted to determine the properties of these soils that are important in this natural disease suppression, the goal being to identify those soil components that function to limit plant disease. Once the important disease-limiting components are identified, the goal would be to transfer these elements to other soils as a means to induce natural biological disease control. These studies demonstrated that growing wheat in orchard soils prior to planting apple, significantly depessed root infection by the fungal pathogen Rhizoctonia solani AG 5. It was shown that wheat suppressed this pathogen by enhancing populations of certain bacteria that are able to inhibit growth of R. solani. However, not all wheat varieties were able to reduce root infection by R. solani. It was shown that wheat cultivars that were best at providing disease control were the same cultivars that supported the highest populations of certain genotypes of the bacterum Pseudomonas putida btp A. The ability to transform resident microbial communities in a manner which induces natural soil suppressiveness will have a significant role in environmentally sustainable systems for management of soilborne plant pathogens.
Technical Abstract: Suppressive soils are characterized by the absence of disease development even though a virulent pathogen and susceptible host are present. Biotic and abiotic elements of the soil environment contribute to suppressiveness, however most defined systems have identified biological elements as primary factors in disease suppression. Managing soil suppressiveness has been suggested as a plausible strategy to employ for the control of soilborne diseases. Results from this study demonstrated that the cultivation of orchard soils with wheat prior to planting apple could induce suppressiveness to Rhizoctonia root rot of apple. However, the induction of disease suppression was limited to specific wheat genotypes. All wheat cultivars examined were uniformly susceptible to infection by the pathogen R. solani AG 8. However, if the pathogen was not introduced to soil until after three successive plantings of the same wheat cultivar, suppression of Rhizoctonia root rot of wheat was observed in the fourth planting, but again only in a wheat genotype specific manner. Wheat culivars that induced soil suppressiveness to the apple pathogen (R. solani AG 5) induced soil suppressiveness to the wheat pathogen. Wheat genotypes that induced soil suppressiveness enhanced populations of specific fluorescent AG 5 and AG 8 in vitro. These results demonstrate the importance of host genotype in modification of indigenous saprophytic microbial communities and suggest an important role for host genotype in the success of biological control.