Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2014
Publication Date: 11/29/2014
Publication URL: http://www.sciencedirect.com/science/article/pii/S092913931400300X
Citation: Strauss, S.L., Stover, D.A., Kluepfel, D.A. 2014. Impact of biological amendments on Agrobacterium tumefaciens soil survival. Applied Soil Ecology. 87:39-48.
Technical Abstract: Paradox, the primary walnut rootstock used in California, is susceptible to Agrobacterium tumefaciens, which causes crown gall. While A. tumefaciens is susceptible to commonly used fumigants such as methyl bromide (MeBr) and Telone-C35 (1,3-dichloropropene and chloropicrin), these fumigants also significantly modify the indigenous soil microbial community, which impacts the ability to inhibit A. tumefaciens populations introduced into these soils. We hypothesized increasing microbial diversity and activity in fumigated soil would provide greater competition for A. tumefaciens, thereby reducing its abundance and limiting disease incidence. Three commercially available soil amendments at multiple rates were tested in native and Telone-C35 fumigated soils in lab experiments: vermicompost and two microbial fermentation mixtures. The amendment-soil mixture was infested with a rifampicin-resistant mutant of A. tumefaciens whose abundance was determined by dilution plating and quantitative PCR over the course of 4 weeks. The two commercial fermentation amendments had no effect on A. tumefaciens population dynamics. However, after a four-week exposure to 10% (w/w) or greater vermicompost, A. tumefaciens populations declined, and in some cases dipped, below detection limits. This suppressive effect appeared to be predominately biotic as heat-treated vermicompost had no impact on A. tumefaciens populations. In addition, culture independent analysis using the Shannon index of diversity found a positive correlation between A. tumefaciens suppression and community diversity. The vermicompost used in this study also provided a consistently similar microbial community in individual batches used over a 9-month period, making it suitable for reliable commercial use.