Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2002
Publication Date: 10/1/2002
Citation: MAZZOLA,M. ., GRANATSTIEN,D.M., ELFVING,,D.C., MULLINIX,K., GU,Y.-., CULTURAL MANAGEMENT OF MICROBIAL COMMUNITY STRUCTURE TO ENHANCE GROWTH OF APPLE IN REPLANT SOILS, PHYTOPATHOLOGY, 92:1363-1366. 2002. Interpretive Summary: Establishment of an orchard on a site previously planted to apple often results in poor tree growth and even death of new trees. This disease phenomenon is termed apple replant disease and typically is controlled through the application of pre-plant soil fumigants, including methyl bromide. In a previous study conducted in this lab, we demonstrated that , in Washington, apple replant disease is caused by a fungal complex. In this study, experiments were conducted to examine the use of short-term wheat cover cropping to manage soil microbial communities and enhance growth of apple in replant soil. All soil ecosystems possess a wealth of biological resources with the ability to control plant diseases. Enhancing populations and environmentally sensitive and biologically sustainable means to control soilborne plant pathogens. This study demonstrated that cultivation of replant soils to wheat enhances populations of resident antagonists resulting in reduced apple root infection by the fungal complex that incites replant disease and improved growth of apple. Future field validation trials are currently in progress but preliminary studies suggest that the above treatments may serve as a viable alternative to soil fumigation for the control of apple replant disease.
Technical Abstract: Replant disease of apple is the primary biological impediment to the establishment of an economically viable orchard on sites previously cultivated to this crop. Control has relied upon the use of soil fumigants, however the impending loss or restricted use of these chemicals necessitates the development of alternative measures for conditions, cultivation of replant soils with wheat prior to planting apple, substantially reduced root infection or infestation by Pythium spp., Rhizoctonia spp. and Pratylenchus penetrans, resulting in enhanced seedling growth. This growth response in apple was stimulated in a wheat cultivar specific manner and was not induced by other grasses including annual ryegrass. Growth-enhancing but not growth-neutral wheat cultivars induced a consistent alteration in certain components of the saprophytic microbial community, including composition of the fluorescent pseudomonad population in replant soils; Pseudomonas fluorescens bv. III dominated replant soils but Pseudomonas putida was the primary species recovered after wheat cultivation of these same soils. Likewise, root exudates from growth enhancing, but not growth neutral, wheat cultivars supported growth of the biocontrol strain P. putida 2C8 when supplied as a sole carbon source. These results suggest that alterations in the fluorescent pseudomonad community, in part, contribute to the