Recently, there has been a growing interest in the biocontrol activity of volatile organic compounds (VOCs) produced by microorganisms. This study specifically focuses on the effects of VOCs produced by the co-culture of Burkholderia vietnamiensis B418 and Trichoderma harzianum T11-W for the control of two phytopathogenic fungi, Botrytis cinerea and Fusarium oxysporum f. sp. cucumerium Owen. The antagonistic activity of VOCs released in mono- and co-culture modes was evaluated by inhibition assays on a Petri dish and in detached fruit experiments, with the co-culture demonstrating significantly higher inhibitory effects on the phytopathogens on both the plates and fruits compared with the mono-cultures. Metabolomic profiles of VOCs were conducted using the solid–liquid microextraction technique, revealing 341 compounds with significant changes in their production during the co-culture. Among these compounds, linalool, dimethyl trisulfide, dimethyl disulfide, geranylacetone, 2-phenylethanol, and acetophenone were identified as having strong antagonistic activity through a standard inhibition assay. These key compounds were found to be related to the improved inhibitory effect of the B418 and T11-W co-culture. Overall, the results suggest that VOCs produced by the co-culture of B. vietnamiensis B418 and T. harzianum T11-W possess great potential in biological control.

This study aimed to investigate the efficiency of the secondary metabolites (SMs) produced by a co-culture of Trichoderma harzianum TW21990 and Burkholderia vietnamiensis B418 in the control of Colletotrichum siamense CM9. A fermentation filtrate of B418 + TW21990 co-culture (BT21) produced a notable increase in the inhibition rate of CM9 compared to those of TW21990 and B418 monocultures, which reached 91.40% and 80.46% on PDA plates and strawberry leaves, respectively. The BT21 fermentation broth exhibited high control efficiency on strawberry root rot of 68.95% in a pot experiment, which was higher than that in the monocultures and fluazinam treatment. In addition, BT21 treatment promoted strawberry root development, improved antioxidative enzyme activities in the leaves and roots, and enhanced the total chlorophyll content of the strawberry leaves. UHPLC-MS/MS analysis of fermentation filtrates was performed to elucidate SM variations, revealing 478 and 795 metabolites in BT21 co-culture in positive and negative ion modes, respectively. The metabolomic profiles suggested abundant SMs with antagonistic capabilities and growth-promoting effects: 3-(propan-2-yl)-octahydropyrrolo [1,2-a]pyrazine-1,4-dione (cyclo(L-Pro-L-Val)), 3-[(4-hydroxyphenyl)methyl]-octahydropyrrolo[1,2-a]pyrazine-1,4-dione (cyclo(L-Pro-L-Tyr)), 3-indoleacetic acid (IAA), 2-hydroxycinnamic acid, 4-aminobutyric acid (GABA), bafilomycin B1, and DL-indole-3-lactic acid (ILA) were significantly enhanced in the co-culture. Overall, this study demonstrates that a co-culture strategy is efficient for inducing bioactive SMs in T. harzianum and B. vietnamiensis, which could be exploited as a novel approach for developing biocontrol consortia.

Root-knot nematodes (RKNs; Meloidogyne incognita) pose a significant threat to tomato crops, necessitating sustainable control methods. This study investigated the inoculation efficacy of co-cultured Burkholderia vietnamiensis B418 and Trichoderma harzianum T11W compared with single-strain treatments for RKNs suppression and their influence on the structure and function of the rhizosphere microbiome. Co-inoculation with B418 + T11W achieved a 71.42% reduction in the disease index, significantly outperforming single inoculations of B418 (54.46%) and T11W (58.93%). Co-inoculation also increased plant height by 38.51% and fresh weight by 76.02% compared to the RKNs infested plants control, promoting robust tomato growth. Metagenomic analysis reveals that co-inoculation enhanced bacterial diversity, with 378 unique bacterial species and a high Shannon index, while fungal diversity decreased with Trichoderma dominance (83.31% abundance). Actinomycetota (46.42%) and Ascomycota (97.92%) were enriched in the co-inoculated rhizosphere, showing negative correlations with RKNs severity. Functional analysis indicates enriched metabolic pathways, including streptomycin and unsaturated fatty acid biosynthesis, enhancing microbial antagonism. Single inoculations altered pathways like steroid degradation (B418) and terpenoid biosynthesis (T11W), but co-inoculation uniquely optimized the rhizosphere microenvironment. These findings highlight co-inoculation with B418 + T11W effectively suppressing RKNs and fostering plant health by reshaping microbial communities and functions, offering a promising approach for sustainable agriculture.