VATIS UPDATE Article

Researchers from USDA-ARS Crops Pathology and Genetics Research Unit, University of California, Davis, the United States, investigated the potential of ASD to manage soilborne populations of Agrobacterium tumefaciens and Pythium ultimum under walnut nursery conditions. Anaerobic soil disinfestation (ASD) is a fumigation-independent strategy for controlling soilborne pathogens. While ASD has been shown to suppress soilborne pathogens for several vegetable crops, it has not been examined for tree-crop diseases.

The following experiment was performed in the late summer of 2013 and 2015: 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 plastic for 6 weeks. Mesh bags of sterile soil infested with either A. tumefaciens or P. ultimum were buried at 15 cm (both trials), 30 cm (first trial), 45 cm (second trial), and 76 cm (second trial) depths prior to ASD treatments. Anaerobic conditions were generated down to 76 cm depth within 1 week and maintained for 6 weeks.

To serve as a comparison, mesh inoculum bags of A. tumefaciens and P. ultimum were buried at the same depths as in ASD trials in adjacent fields that were fumigated with Telone C-35 at the maximum allowable rate. In both field trials, ASD exhibited pathogen suppression similar to traditional chemical fumigation. A. tumefaciens and P. ultimum populations were reduced below detection limits during both chemical fumigations. In the ASD treatments, 30% of the samples had A. tumefaciens populations below detection limits, while the remaining replicates had populations that were significantly lower than the no treatment control populations.