Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 9/22/2011
Publication Date: 11/6/2011
Citation: Mazzola, M. Potential of biofumigation for soilborne pest control in strawberry. pp 47.1-47.2, In, Proceedings Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. MBAO, Fresno, CA 2011. Interpretive Summary: The term “biofumigation” was coined to describe the process by which control of soil-borne diseases is obtained in response to soil incorporation of Brassica plant residues. Conventionally disease control has been attributed to the generation of biologically effective chemical compounds resulting from the breakdown of specific substances contained in the cells of the Brassica plant. Studies were conducted to determine whether soil incorporation of Brassica seed meals, a waste product remaining after extraction of oil from seed, could provide effective control of the fungal pathogen Macrophomina phaseolina which causes the disease charcoal rot of strawberry. All Brassica seed meals tested diminished populations of this fungal pathogen in soil, and the same result was obtained whether or not the seed meal applied to soil resulted in production of a fungicidal compound. In addition, suppression of the pathogen and disease control was only obtained when the experiment was conducted in a natural soil, and no disease control was observed when the same studies were conducted in a soil which was pasteurized, to reduce the native soil biology, prior to introduction of the pathogen. These data demonstrate that control of charcoal rot of strawberry in response to seed meal may require biological processes that are brought about by seed meal application to soil and is not a function of chemical activities alone.
Technical Abstract: Macrophomina. phaseolina is a pathogen of emerging importance in strawberry production systems. Studies were conducted to assess the capacity of Brassicaceae seed meals to suppress charcoal rot of strawberry caused by this pathogen and to determine the relative contribution of seed meal derived chemistry and soil biology in disease control. Brassicaceae seed meal amendments suppressed proliferation of M. phaseolina through soil systems, but optimal seed meal-induced pathogen suppression required a functional soil biology. Suppression of M. phaseolina was obtained with seed meal sourced from various brassicaceae species and was not associated with production of a biologically active chemistry (e.g. allyl isothiocyanate by Brassica juncea. Pathogen suppresssion observed in natural soil, was abolished when seed meal amended soils were pasteurized prior to infestation with M. phaseolina. In total these findings indicate that biological mechanisms contributed significantly to the disease control that was observed. In small scale field trials B. juncea seed meal amendment suppressed artificially elevated populations of M. phaseolina but did not provide effective disease control. When trials were repeated a B. juncea/Sinapis alba formulation, suppressed soil densities of the pathogen and significantly suppressed strawberry root infection. Across trials conducted in controlled and field environments there has been a lack of consistent association between the effect of seed meal amendment on M. phaseolina soil density and resulting level of root infection. This suggests that the observed disease control may have a greater dependence upon microbial interactions that transpired in the rhizosphere than that which occurs in the bulk soil environment.