Incorporation of Brassica seed meal soil amendment and wheat cultivation for control of Macrophomina phaseolina in strawberry

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 the abundance of M. phaseolina detected in 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 functional role of soil biology in disease suppression 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 additive effect on disease suppression 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.