Plant-Derived Biostimulant Supports Biocontrol Microbial Inoculant and Reduces Phythophthora Blight.

Phytophthora blight is a serious threat to the Midwest vegetable industry, because the oomycete pathogen responsible for this disease, Phytophthora capsici, has a wide host range, can spread quickly in fields, and produces resilient oospores that can survive in soil for years. Phytophthora capsici has also become resistant to commonly used fungicides and resistant crop varieties are rare. Amending soil with biostimulants derived from plant biomass has been shown to promote plant growth, improve nutrient-use efficiency and help plants withstand abiotic and biotic stress. Because soil microorganisms are generally better competitors for amino acids and peptides in these products than plants, the benefits are expected to be due, at least in part, to changes in microbial community structure and activity. These products also have potential to aid in the establishment and survival of key biocontrol microbial inoculants such as Trichoderma species. To test these hypotheses, we conducted an experiment to determine how these amendments would alter rhizosphere microbial community structure in pepper and affect the potential for pepper plants to withstand Phytophthora blight. Soil was subject to one of the four following treatments: 1) control (no amendment), 2) biostimulant, 3) Trichoderma, 4) biostimulant + Trichoderma. Pepper seedlings were transplanted into each pot, and pots were amended with either P. capsici propagules or a sterile water control. After 28 days, rhizopshere microbial communities were collected from pepper roots and subject to culture dependent and independent analyses, and pepper biomass was determined. Results indicate that each amendment treatment altered pepper rhizosphere community structure, and the biostimulant+Trichoderma helped pepper plants to withstand Phytophthora blight. Findings from this study provide evidence that biostimulants could increase the efficacy of biocontrol inoculants and improve the productivity of vegetable crops.