Impact of wheat cultivation on microbial communities from replant soils and apple growth in greenhouse trials

Studies were conducted to assess the impact of short-term rotations of whea t on microbial community composition and growth of apple in soils from repl ant orchard sites. Soils from two orchards were cultivated with three succe ssive 28-day growth cycles of 'Eltan','Penewawa', or 'Rely' wheat in the gr eenhouse and subsequently planted to 'Gala' apple seedlings. Cultivation of orchard replant soils with any of the three wheat cultivars enhanced growt h of apple relative to that achieved in untreated soils. Improved growth wa s associated with a marked reduction in apple root infection by species of Rhizoctonia and Pythium. Populations of plant-parasitic nematodes were belo w damage threshold levels in these orchard soils; however, apple seedlings grown in wheat-cultivated soils had significantly lower root populations of Pratylenchus spp, than did seedlings grown in untreated soils. Growth of a pple in 'Penewawa'-cultivated soils often was superior to that observed in soils planted with 'Eltan' or 'Rely'. In untreated orchard soils, fluoresce nt pseudomonad populations isolated from soil and the apple rhizosphere wer e dominated by Pseudomonas fluorescens biotype C and Pseudomonas syringae. Cultivation of replant soils with wheat induced a characteristic transforma tion of the fluorescent pseudomonad population, and Pseudomonas putida domi nated the population of this bacterial group recovered from wheat-cultivate d replant orchard soils. Results from this study suggest that use of short- term wheat cropping sequences during orchard renovation could be useful in management of replant disease and that this disease-control option may oper ate, in part, through modification of the fluorescent pseudomonad community .