Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2003
Publication Date: 10/23/2003
Citation: Gu, Y., Mazzola, M. 2003. GENETIC MODIFICATION OF THE FLUORESCENT PSEUDOMONAD COMMUNITY AND CONTROL OF APPLE REPLANT DISEASE INDUCED IN A WHEAT CULTIVAR-SPECIFIC MANNER. Applied Soil Ecology. 24:57-72.
Interpretive Summary: The 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 croping to manage soil microbial communities and enhance growth of apple in replant soils. All soil ecosystems possess a wealth of biological resources with the ability to control plant diseases. Enhancing populations and activity of these organisms has the potential to serve as an environmentally sensitive and biologically sustainable means to control soilborne plant pathogens. This study demonstrated that cultivation of replant soils to certain wheat genotypes 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 peviously cultivated to this crop. Cropping of replant soils with specific wheat genotypes prior to planting apple, substantially reduced root infection by Cylindrocarpon and Rhizoctonia spp. and enhanced seedling growth. The growth respone in apple was stimulated in a wheat cutlivar specific manner. Growth-enhancing but not growth-neutral wheat cultivars induced consistent changes in composition of the resident fluorescent pseudomonad population; Pseudomonas fluorescens bv. III and P. syringae dominated replant soils but Pseudomonas putida was the primary species recovered from soils after cropping with growth-enhancing wheat cultivars. Genetic composition of the fluorescent pseuodomonad community and antagonistic capacity of the fluorescent pseudomonad community toward fungal plant pathogens also varied in a wheat cultivar-specific manner. These results suggest that alterations in the fluorescent pseudomonad community, in part, contributed to the observed suppression of apple replant disease observed in response to wheat cultivation. This study demonstrates the significant role of plant genotype in determining composition of the saprophyytic soil microbial community and establishes the need to cosider plant genotype when evaluating benefits of specific cover crops for management of soilborne plant diseases.