Volatile-mediated suppression of cucumber damping-off by Chryseobacterium gleum isolated from compost-amended soils

Compost-based soil amendments are widely used to enhance soil health and suppress soil-borne plant diseases. These effects are often linked to changes in microbial activity and volatile organic compound (VOC) production. In this study, we investigated the effects of compost amendment on soil VOC profiles and the role of bacterial antagonists isolated from compost-amended soil in suppressing cucumber damping-off caused by Pythium aphanidermatum. Compost amendment altered the soil volatilome, increasing the diversity and relative abundance of several volatile compounds compared to non-amended soil. Nine bacterial isolates recovered from compost-amended soil were screened for antagonistic activity. Among these, Chryseobacterium gleum B2 showed the strongest and most consistent antagonistic activity, significantly inhibiting the mycelial growth of P. aphanidermatum in vitro and reducing damping-off incidence by 50% in a greenhouse pot experiment. A sealed plate assay (absence of direct contact) showed that VOCs released by C. gleum B2 directly suppressed P. aphanidermatum growth. The GC–MS analysis of VOCs produced by C. gleum B2 showed that it produced a complex VOC profile, dominated by l-alanine ethylamide (S), 1-dodecene, and dimethyl disulfide, along with short-chain ester derivatives. Overall, these results indicate that compost amendment and its associated bacterial populations show VOC-mediated antagonistic activity towards P. aphanidermatum. The VOCs produced by C. gleum B2 suppressed cucumber damping-off caused by P. aphanidermatum under greenhouse conditions. The study highlights the potential of VOC-mediated biocontrol as a component of sustainable management strategies for soil-borne plant diseases.