Field evaluation of reduced rate Brassicaceae seed meal amendment and rootstock genotype on the microbiome and control of apple replant disease

Authors: WANG, LIKUN - Washington State University; Mazzola, Mark

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2019
Publication Date: 3/19/2019
Citation: Wang, L., Mazzola, M. 2019. Field evaluation of reduced rate Brassicaceae seed meal amendment and rootstock genotype on the microbiome and control of apple replant disease. Phytopathology. 109(8):1378-1391. https://doi.org/10.1094/PHYTO-02-19-0045-R.
DOI: https://doi.org/10.1094/PHYTO-02-19-0045-R

Interpretive Summary: Organic soil amendments often have been promoted as a means to control soilborne plant diseases. However, the effective use of individual amendments for the control of biologically complex diseases seems improbable. Studies were conducted to assess whether the effective control of apple replant disease could be controlled at significantly lower Brassicaceae seed meal(SM) amendment rates than used previously if used in conjunction with the appropriate apple rootstock. Significant interactions were detected between seed meal formulation application rate and apple rootstock genotype in terms of rhizosphere microbiome composition, plant growth and root infection by two pathogens that contribute to apple replant disease; Pythium spp. and lesion nematode (Pratylenchus penetrans). Although Gala apple growth and production was improved at all Brassicaceae SM application rates regardless of genotype, spring SM application and planting resulted in significant mortality of Gala/M.26 trees but not Gala/G.41 trees. SM amendment significantly increased tree yields in a manner similar to pre-plant soil fumigation. A 1/3rd reduction in SM rate (4.4 t ha-1) relative to the full rate used previously (6.6 t ha-1) provided similar levels of disease control but reduced incidence of tree death due to phytotoxicity. All SM treatments effectively reduced root infestation by P. penetrans and did so for a much longer period (2 years) than did pre-plant soil fumigation. Superior nematode suppression was observed when the SM treatment was used in conjunction with Gala/G.41 than Gala/M.26 trees. Findings from this study demonstrated that use of the appropriate apple rootstock genotype will allow for effective replant disease control at SM application rates significantly less than that utilized previously.

Technical Abstract: An orchard field trial was conducted to assess the utility of reduced rate Brassicaceae seed meal (SM) amendment in concert with specific rootstock genotypes for effective control of apple replant disease. Three amendment rates of a 1:1 formulation of Brassica juncea/Sinapis alba SM were compared to pre-plant 1,3-dichloropropene/chloropicrin soil fumigation for disease control efficacy. At the highest rate (6.6 t ha-1) in the spring of planting, SM caused significant phytotoxicity and tree mortality for Gala.M26 trees. Phytotoxicity was not observed at SM application rates of 2.2 or 4.4 t ha-1. SM treatment resulted in growth and yield increases of Gala.M.26 and Gala.G.41 trees in a manner similar to soil fumigation and significantly greater than the no treatment control. A 1/3rd reduction in SM amendment rate resulted in tree growth and yield that was similar or superior to that obtained with the full SM rate (6.6 t ha-1). Soil fumigation and all SM treatments reduced Pratylenchus penetrans root infestation relative to the control treatment at the end of the initial growing season, but root densities were higher for Gala/M.26 than Gala/G.41. Lesion nematode root densities rapidly recovered in the fumigation treatment and were indistinguishable from the control at the end of the second growing season. Soil fumigation and all SM treatments significantly suppressed Pythium spp. root infection relative to the control. Trees grafted to rootstock G.41 possessed lower P. penetrans root densities relative to trees grafted to rootstock M.26. Composition of microbial communities from SM-amended soils was distinct from those detected in control and fumigated soils, and the differences were amplified with increasing SM application rate. Specific fungal and bacterial phyla associated with suppression of plant pathogens were more abundant in SM-treated soil relative to the control and were similar in abundance in 4.4 and 6.6 t ha-1 SM treatments. Findings from this study demonstrated that use of the appropriate apple rootstock genotype will allow for effective replant disease control at SM application rates significantly less than that utilized previously (6.6 t ha-1).