Suppression of Phytophthora Blight of Pepper by Biochar Amendment is Associated with Improved Soil Bacterial Properties

Biochar amendment effectively controlled the Phytophthora blight of pepper and suppressed the pathogen abundance, with biochar applied just before transplanting (BC0) producing greater effects than that applied 20 days before transplanting (BC20). Biochar treatments stimulated the proliferation of total bacteria, Bacillus spp., Pseudomonas spp. , Streptomyces spp., and Sphingomonas spp. The proliferative effect of BC20 treatment gradually weakened compared to that of BC0 treatment with extended planting time. Moreover, biochar amendment strongly promoted the antagonist percentage and antagonistic ability of total bacteria, Bacillus spp., and Pseudomonas spp. and the promoting effect of BC0 treatment was stronger than that of BC20 treatment. Biochar-enriched Bacillus and Streptomyces strains, followed by Pseudomonas strains, were the best in terms of reducing the abundance of P. capsici and controlling Phytophthora blight of pepper. In addition, MiSeq sequencing data indicated that biochar treatments altered the soil bacterial community and enriched some beneficial bacteria, with BC0 treatment producing greater effects than BC20 treatment. Overall, the biochar-induced improvement of soil properties (particularly the abundance of biocontrol bacteria such as Bacillus spp., Pseudomonas spp. and Streptomyces spp. and bacterial antagonisms against P. capsici) may constitute one of the important mechansims of biochar-mediated control of Phytophora blight of pepper.