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

Abstract BACKGROUND 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). RESULTS 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. CONCLUSION 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.