Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2017
Publication Date: 2/2/2017
Citation: Mazzola, M., Agostini, A., Cohen, M.F. 2017. Incorporation of brassica seed meal soil amendment and wheat cultivation for control of macrophomina phaseolina in strawberry. European Journal of Plant Pathology. doi: 10.1007/s10658-017-1166-0. 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, and a wheat cover crop used alone or together, 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. Prior cultivation of soils with certain wheat varieties prior to planting strawberry yielded greater disease control than seed meal amendment. Integration of the two methods did not provide a superior level of disease control relative to that attained when using the methods independently. These data demonstrate that control of charcoal rot of strawberry in response to seed meal amendment or prior wheat cultivation may require biological processes that are brought about by their application to soil and is not a function of chemical activities alone.
Technical Abstract: Macrophomina phaseolina is the cause of charcoal rot, a disease of emerging importance in strawberry production systems. Brassicaceae seed meals (SM) and prior cultivation of soils with wheat, were evaluated for the capacity to suppress charcoal rot of strawberry 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 SM-induced pathogen suppression required a functional soil biology. Suppression of M. phaseolina was obtained with SM sourced from various brassicaceae species and was not associated with a biologically active chemistry such as that generated by Brassica juncea SM amendment (e.g. allyl isothiocyanate). Disease control observed in natural soil was abolished when SM amended soils were pasteurized prior to infestation with M. phaseolina, suggesting a role for soil biology in suppression of disease that was observed. Cultivation of soils with wheat prior to pathogen infestation resulted in a level of disease control superior to SM amendment, however no significant benefit was observed with integration of the two treatments. In small scale field trials, SM amendment induced phytotoxicity was observed and may have contributed to a lack of apparent control of charcoal rot. In the same trials, significant weed control was achieved in response to SM amendment. Across trials conducted in controlled and field environments there has been a lack of consistent association between the effect of SM amendment or wheat cultivation 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 transpire in the rhizosphere than that which occurs in the bulk soil environment.