Modification of fluorescent pseudomonad community and control of apple replant disease induced in a wheat cultivar-specific manner

Apple orchard soils were cropped for three successive 28-day growth cycles with a perennial ryegrass/annual ryegrass mixture or 1 of 11 wheat cultivars prior to planting with Gala apple seedlings. Prior cropping of soils with ryegrass had no significant impact on growth of apple, but cultivation with some, but not all, wheat cultivars substantially enhanced apple seedling growth. Enhanced growth of apple was associated with a reduction in root infection by the dominant fungal pathogens resident to the respective orchard soils. Wheat cultivars that enhanced growth of apple modified the genetic and species composition of the fluorescent pseudomonad population resident to orchard soil. The fluorescent pseudomonad population from soils cropped with wheat cultivars that enhanced apple seedling growth possessed a higher capacity to inhibit in vitro growth of multiple elements of the fungal complex that incites apple replant disease than did the population from non-treated orchard soil or soil cropped with a wheat cultivar that did not enhance growth of apple. Application of wheat root exudates to soil also modified the antagonistic potential and composition of the fluorescent pseudomonad population in a cultivar-specific manner. This study demonstrates the significant role of plant genotype in determining composition of the saprophytic soil microbial community. It also establishes the need to consider not only plant species but also plant genotype when evaluating the potential benefit of specific cover crops as a component within a systems approach for the management of soilborne plant diseases. Published by Elsevier B.V.