Efficacy of new biocontrol agents against Rhizoctonia solani in lettuce evaluated through an automated imaging system and their effect on bacterial soil communities

In recent years, biocontrol agents (BCAs) have gained attention as sustainable alternatives or complements to synthetic chemicals for managing phytopathogens and enhancing plant growth. In this study, six bacterial strains were evaluated as BCAs against Rhizoctonia solani (RS), a soil-borne pathogen affecting economically important crops. Two strains (Bacillus sp. B04A33 and Psychrobacillus sp. B04A42) were isolated from maize embryos, while Lactiplantibacillus plantarum strains (ITEM 17215, ITEM 17218, ITEM 18335 and S61) originated from food or animal sources. A commercial Trichoderma-based product (REMEDIER®, Gowan Italia) served as the control. Biocontrol effectiveness was assessed both in vitro and in vivo on lettuce using an automated imaging system for plant growth monitoring. In soils infected by R. solani, the inoculum of strains B04A33, B04A42, and S61 enhanced germination and seedling vigor, and increased dry weight of shoots and roots. Root system development, analyzed via image processing in Matlab, confirmed improved growth. The qPCR analysis of soil samples showed that microbial abundance increased in non-treated (NT) and S61 + RS treatments, while R. solani levels decreased in B04A33 + RS and B04A42 + RS. Oxford Nanopore MinION sequencing of soil samples revealed dominance of Pseudomonadota, Actinomycetota, and Bacillota, with enrichment of Bacillaceae and Lactobacillaceae in B04A42 and S61 treatments, confirming the successful establishment of the inoculated strains within the soil microbiome. These results support both the potential of selected bacterial strains as effective BCAs against RS and the use of automated imaging in BCAs screening procedures, promoting sustainable and technology-assisted crop management.