Biocontrol Practices Alter Rhizosphere Community Structure in Phytophthora Capsici Infested Soil and Increase Pepper Growth.

Phytophthora blight has become one of the most serious threats to the vegetable industry in the Midwest U.S. Controlling Phytophthora capsici, the pathogen responsible for Phytophthora blight is difficult because it has a broad host range, spreads rapidly under ideal environmental conditions, and produces resilient spores that can survive indefinitely in soil. There is insufficient resistance in crop varieties, and P. capsici is resistant to many fungicides. Biocontrol practices that are thought to suppress soil-borne pathogens via changes in soil microbial communities could help control Phytophthora blight, but the mechanisms are not well understood which limits effective deployment of these practices. In this study, we determined whether various cover crop species grown alone, or in combination with a biochar amendment made from softwood forest species, could suppress Phytophthora blight in two naturally infested field soils. Changes in the rhizosphere community structure of a subsequently planted pepper crop were quantified in select treatments with semi-selective media and 16S sequencing performed by Illumina MiSeq and analyzed using QIMME. A wheat cv. Penewawa cover crop and biochar, alone and in combination, increased pepper root and shoot biomass, and increased the abundance of Pseudomonas fluorescens in both soils. In the low organic matter soil, P. capsici abundance was reduced most by treatments that received the wheat cover crop, whereas in the high organic matter soil, P. capsici was reduced most by treatments that received biochar. Results of sequencing analyses indicated that many microbial taxa increased in response to the biocontrol treatments, and there was some overlap across soils, but soil type also played a role. These results indicate that including a wheat cover crop in rotation, and applying biochar can improve pepper growth in soil infested with P. capsici, but the most effective strategy could vary given soil type.