Effect Biocontrol Activity of Bacillus velezensis S161 Against Green Mould Through Volatile Organic Compound Regulation

Postharvest green mould of citrus, caused by Penicillium digitatum , frequently incurs severe decay losses. Chemical control strategies are plagued by multiple drawbacks, rendering biological control a promising alternative. Bacillus velezensis S161 suppresses the growth of the pathogen; with HS‐SPME/GC–MS and multivariate stats we now map how it works and how it re‐sculpts fruit volatiles. The results showed that S161 treatment reduced the incidence of green mould to 50.9% and obviously alleviated disease severity. Inoculation with S161 alone induced the upregulation of antifungal VOCs such as α‐pinene and linalool, maintaining the normal metabolism of citrus fruit. Conversely, P. digitatum infection promoted the synthesis of signal molecules (e.g., D‐limonene and pinene) that facilitate pathogen colonization. Co‐treatment with S161 and P. digitatum downregulated various metabolites unfavourable for disease control, while obviously upregulating four compounds, namely acetic acid, styrene, trimethyl ethyl citrenate and 2‐phenylethyl nicotinate; notably, acetic acid has been confirmed to possess distinct antifungal activity. The core regulatory pathways involved monoterpenoid biosynthesis, limonene and pinene degradation, as well as glycolysis and gluconeogenesis. Thus, S161 redirects citrus VOC metabolism to suppress green mould, providing both a ready‐to‐use strain and target metabolites for future biocontrol formulations.