Biocontrol practices alter Rhizosphere community structure in Phytophthora capsici infested soil and increase pepper growth

Biocontrol practices alter rhizosphere community structure in Phytophthora capsici infested soil and increase pepper growth 1*Hoagland, L., 2Egel, D., 1Cerruti, N., 3Thimmapuram, J., 3Colling, C., 3Bhide, K. 1Department of Horticulture and Landscape Architecture, Purdue University; 2Department of Botany and Plant Pathology, Purdue University; 3Bioinformatics Core Facility, Purdue University 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 also insufficient resistance in crop varieties, and P. capsici is now 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, though the mechanisms are not well understood limiting the effective deployment of these practices. In this study, we evaluated the potential for various cover crop species grown alone, or in combination with a biochar amendment made from hardwood forest species to suppress Phytophthora blight in two naturally infested field soils. Changes in the rhizosphere community structure of a subsequently planted pepper crop were quantified with semi-selective media and 16S sequencing performed by Illumina MiSeq and analyzed using QIMME. A wheat cover crop and biochar, alone and in combination, increased pepper root and shoot biomass, and increased the abundance of Pseudomonas fluorescens in the pepper rhizosphere in both soils. In the low organic matter soil, P. capsici abundance in the pepper rhizosphere 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. These results indicate that including a wheat cover crop and applying biochar can improve pepper growth in soil infested with P. capsici, though the suppression mechanisms and most effective biocontrol strategy could vary given soil type. Results of on-going sequencing analyses will provide additional insights to the potential mechanisms regulating P. capsici suppression and enhanced pepper growth observed in this study.