Endophytic Bacteria as a Biocontrol Agent: Variability in Effectiveness Across Different Growing Environments

Abstract

The effectiveness of biocontrol agents (BCAs) in different growth media, including soil and soilless systems, remains inadequately understood. This study aimed to evaluate the effectiveness of endophytic bacteria (EB) in controlling bacterial angular leaf spot (ALS) disease in cucumbers grown in different growing media (GM). Cucumbers were cultivated in non-sterile soil, sterile hydroponic, and substrate-based media. The study assessed the population dynamics of the EB Acinetobacter calcoaceticus G118K1T, the bacterial pathogen Pseudomonas syringae pv. lachrymans (Psl), ALS disease progression, and expression of resistance-related genes (PR1 and PR3) in seedlings. Additionally, the impact of these factors on plant growth and health was evaluated. In the early stages, GM influenced disease development. The application of EBG118K1T suppressed disease severity and progress by 26% to 40% across all GM. However, the extent of disease suppression varied depending on the GM. GM significantly affected the Psl population. In EB-treated plants, the Psl population reached a maximum of 106CFU/g-shoots, whereas in the positive control (PC), it reached 107CFU/g-shoots. The resistance induced by G118K1T was activated across all GM without significant differences in PR1 and PR3 gene expression levels. Plant biomass varied significantly influenced by GM, Psl, EB G118K1T and their interactions. The ability of EB to colonize internal plant tissues presents a significant advantage for its use in diverse growing systems. However, its effect on plant health and development varies across different systems.