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Effect of anaerobic soil disinfestation and vermicompost on soilborne phytopathogenic agents under tree-crop nursery conditions
S. STRAUSS (1), D. Kluepfel (2), G. Browne (3). (1) USDA ARS, Davis, CA, U.S.A.; (2) USDA-ARS CPGRU, Davis, CA, U.S.A.; (3) USDA-ARS, Davis, CA, U.S.A.

Anaerobic soil disinfestation (ASD) is a fumigation-independent management strategy for controlling soilborne pathogens. Walnut nurseries currently employ preplant fumigation to control soilborne phytopathogens and weeds, and may be amenable to use ASD instead. We investigated the potential of ASD and post-ASD vermicompost applications to manage seed-borne populations of <i>Agrobacterium tumefaciens</i> and other soilborne phytopathogens in walnut nursery conditions. Rice bran at 20 metric tons/ha was applied to ASD plots, irrigated for 24 h (13 cm of water, 1 drip emitter per 930 cm2), and covered by TIF for 6 weeks. Mesh bags of sterile soil inoculated with either <i>A. tumefaciens</i> or <i>Pythium ultimum</i> were buried prior to ASD treatments. Anaerobic conditions were reached at 18” depth within 1 week and maintained for 6 weeks. <i>A. tumefaciens</i> and <i>P. ultimum</i> populations were reduced below detection limits during ASD as determined by dilution plating. Next-generation sequencing of DNA extracted from soil revealed significant differences in the soil microbial community after ASD. To examine effects of ASD efficacy and post-ASD vermicompost application on disease incidence, Paradox walnut seeds were dipped in <i>A. tumefaciens</i> inoculum prior to planting. The abundance of <i>A. tumefaciens</i> on walnut seeds planted in ASD and control plots with vermicompost was significantly less than plots without vermicompost.

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