Soil biota from newly established orchards are more beneficial to early growth of cherry trees than biota from older orchards

Growth of young fruit trees replanted into old orchard soil is often poor relative to growth in soil that has not previously been planted with fruit trees. There is evidence that a consortium of deleterious soil biota, commonly referred to as the replant disease complex, are responsible for this poor early growth. We used a bioassay, comparing cherry plant growth in sterilized and non-sterilized subsamples of soil, to assess the net effect of soil biota from 18 orchards in the Okanagan Valley of British Columbia, Canada with differing histories of fruit tree production (previously cropped 'old' orchards, and not previously cropped 'young' orchards). Generally, shoot height increment was larger in non-sterile soil from young orchards than from old orchards (two-factor ANOVA; P < .001). When soil from young orchards was sterilized plant weight was lower, compared to the non-sterilized counterpart (two-factor ANOVA; P = .006). Pratylenchus populations in root tissue were greater in plants grown in old orchard soils than in young orchard soils (one-factor ANOVA; P < .001). Multiple regression analyses showed that FDA hydrolysis, an indicator of microbial activity, was the only variable that significantly predicted plant growth response to sterilization for the variables shoot height increment (R-2 = 0.6; P = .001) and plant weight (R-2 = 0.5; P = .002). Overall, results from this study suggest that management practices that stimulate microbial activity will benefit growth of cherry trees in previously cropped 'old' orchards, and not previously cropped 'young' orchards.