Solid‐State Fermentation and Biocontrol Effects of Mycorrhiza Helper Streptomyces Agents on Pepper Phytophthora Blight

ABSTRACT The liquid agents of two mycorrhiza helper (MH) Streptomyces strains, S. tricolor (STr), and S. tendae (STe), were confirmed to suppress Phytophthora blight of pepper ( Capsicum annuum L.) in a former pot experiment. In terms of practicality, it is urgent to prepare solid microbial agents and test their actual effects on the community diversity and vitality of soil AM fungi. First, by adjusting the formulation and fermentation conditions, the optimal C/N ratio and main C source for STr and STe were determined as 34.9 and maize flour, and 43.6 and millet flour, respectively, while pH 7.5, material‐to‐water ratio 1:1 and 15% inoculation volume were chosen for both strains. Second, by test in a greenhouse pot experiment, the two prepared solid MH agents increased soil AM fungal diversity and colonization, and decreased pepper Phytophthora blight severity. Specifically, STe more effectively elevated AM fungal population, colonization, and P‐promoting function, while STr aggressively enhanced the uptake efficiency of K, the strongest crucial factor controlling blight. On the whole, the blight severity negatively correlated to AM fungal population size, diversity index and colonization rate, while the fruit yield and shoot biomass negatively correlated to blight severity. In summary, two solid MH agents which could promote the diversity and functionality of soil indigenous AM fungal community were successfully developed to suppress pepper Phytophthora blight.