Biocontrol of Phytophthora Blight with Forest Industry Residuals.

Abstract

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 up to ten years. Resistant crop varieties are rare and P. capsici is now resistant to many commonly used fungicides. Amending soil with complex organic substrates has potential to suppress P. capsici infection and increase vegetable productivity via biocontrol mechanisms. Indiana has a significant forest industry with residual products that could be used as locally available amendments to meet this goal. In this study, soil from two farms with recent outbreaks of Phytophthora blight were collected for use in greenhouse trials. One of the soils had high and the other had low total organic matter. Soils were amended with one of five forest industry residuals alongside a control (no amendment) treatment, at rates of 1% and 3% of total soil carbon. Following a one month incubation period, susceptible pepper seedlings (cv. Red Knight) were transplanted into each pot, and pots were inoculated with P. capsici zoospores to ensure sufficient pathogen pressure. Pepper plants were harvested after 37 days and soil microbial community structure, percent root infection by P. capsici, and plant above and belowground biomass determined. Results to date indicate that many of the treatments altered microbial community structure, particularly in the low organic matter soil, resulting in greater total microbial biomass and greater populations of actimomycetes and arbuscular mycorrhizal fungi. Several treatments also resulted in lower P. capsiciroot infection and increased pepper biomass.  These results indicate that forest industry residuals could be used to improve soil quality and biologically control Phytophthora blight.

 Keywords: Phytophthora capsici, soil suppressiveness, organic amendments