Methyl thiobutyrate: A microbial volatile compound with dual modes-of-action against root-knot nematodes

Root-knot nematodes (RKN; Meloidogyne incognita) cause severe losses in tomato production, driving the need for sustainable control strategies. Methyl thiobutyrate (MTB), a volatile organic compound produced by the biocontrol bacterium Bacillus cereus Bc-cm103, was investigated for its nematicidal activity and underlying modes-of-action (MoAs).

MTB exhibits direct contact toxicity, with a 12-h median lethal concentration (LC₅₀) of 48 μg mL^-1 against second-stage juveniles (J2) and a median effective concentration (EC₅₀) of 89 μg mL^-1 for inhibiting egg hatching. In pot assays, soil drenching with MTB at 100 μg mL^-1 reduced gall formation by 89.8%, whereas application at 20 μg mL^-1 achieved 84.6% control efficacy. Additionally, when applied as a volatile fumigant without direct root contact, MTB provided 41.7% control efficacy. Furthermore, split-root and foliar spray assays revealed that MTB triggers plant defense responses suggestive of induced systemic resistance in tomato plants, achieving control efficacies of 60.5% and 45%, respectively. Mechanistic studies revealed that MTB disrupts nematode cell membrane integrity and induces apoptotic-like morphological changes associated with upregulation of MI-asp1. Transcriptome analysis of MTB-treated tomato roots showed significant enrichment of defense-related pathways, including plant hormone signal transduction (SA/JA/ET), MAPK signaling and phenylpropanoid biosynthesis, providing molecular evidence for the observed systemic resistance.

MTB controls RKN through a dual MoA involving direct contact toxicity, fumigant activity and the induction of systemic resistance in plants. This multifaceted activity highlights MTB's significant potential as an eco-friendly nematicide for integrated nematode management. © 2026 Society of Chemical Industry.