Soil biota from newly established orchards are more beneficial to early growth of cherry trees than biota from older orchards
Munro, P., Forge, T.A., Jones, M.D., Nelson, L.M. (2020). Soil biota from newly established orchards are more beneficial to early growth of cherry trees than biota from older orchards. Applied Soil Ecology, [online] 155 http://dx.doi.org/10.1016/j.apsoil.2020.103658
Plain language summary
Renewal of the tree fruit industry, adopting more profitable varieties and efficient high-density production systems, depends on replanting old orchards. However, young fruit trees that are replanted into old orchard sites often grow very poorly. This syndrome, known as replant disease, is the result of a complex mix of nematode roundworm pests and pathogenic fungi that build up over time in the soil of old orchards. Orchardists would benefit from being able to anticipate the severity of replant disease in orchard sites they are planning to replant. Most previous research on orchard replant disease has been conducted on apple. This study was designed to assess the influences of cherry orchard age and soil properties, including biological indicators of soil health, on populations of plant-parasitic nematodes and replant disease of cherry seedlings. The analyses were conducted on soil samples taken from 18 orchards in the Okanagan Valley that varied in age from 0 (native vegetation prepared for first planting) to 21 years. Results of the study confirmed that overall replant disease was worse, and nematode parasitism of cherry seedlings was greater, in soil from older than younger cherry orchards. The data also showed that replant disease potential was inversely related to overall soil microbial activity. These results suggest that adoption of orchard management practices that foster soil microbial activity may reduce the severity of replant disease when orchards are eventually replanted, and that measurements of plant-parasitic nematode populations and overall soil microbial activity can help orchardists predict the potential severity of replant disease.
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 (R2 = 0.6; P = .001) and plant weight (R2 = 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.