Soil Suppressiveness Against Pythium aphanidermatum in Relation to Microbial Community Composition in Vegetable Fields

Abstract

Soil suppressiveness against Pythium aphanidermatum was evaluated in relation to microbial community composition in vegetable fields to understand the biological basis of disease suppression in agroecosystems. Soil samples were collected from fields exhibiting varying levels of damping-off incidence, and suppressiveness was assessed through pathogen inoculation assays under controlled conditions. Microbial community structure was analyzed using culture-dependent isolation and functional group assessment of bacteria, fungi, and actinomycetes. Results indicated significant variation in soil suppressiveness, with certain soils consistently reducing disease severity and pathogen survival. Suppressive soils were characterized by higher microbial diversity and greater abundance of antagonistic microorganisms, including fluorescent Pseudomonas, Bacillus spp., and Trichoderma-like fungi. In contrast, conducive soils showed reduced microbial diversity and dominance of less competitive microbial assemblages, favoring pathogen establishment. Correlation analysis demonstrated a strong relationship between microbial activity levels and reduced Pythium infection rates, suggesting that microbial competition, antibiosis, and niche exclusion contribute to disease suppression. Soil physicochemical properties, particularly organic carbon content and moisture stability, further influenced microbial community structure and suppressive potential. The findings highlight the critical role of soil microbiome composition in regulating soil-borne plant pathogens and emphasize the importance of maintaining biologically active soils. These results support the integration of soil health management practices, such as organic amendments and crop rotation, to enhance natural suppressiveness against Pythium aphanidermatum in vegetable production systems.