Inhibitory activity and mechanism of volatile organic compounds from Bacillus velezensis HC-10 against honeysuckle leaf spot disease

Abstract

Alternaria alternata, a pathogenic fungus responsible for honeysuckle leaf spot disease, causes substantial economic losses in honeysuckle cultivation. While chemical pesticides remain the primary control measure, their use poses significant risks to human health and the environment. Consequently, there is a growing demand to explore eco-friendly and sustainable alternatives to chemical control methods. In this study, Bacillus velezensis HC-10 was isolated from honeysuckle leaves and exhibited a notable inhibition rate of 66.74 % against A. alternata in plate assays. The volatile organic compounds (VOCs) produced by HC-10 demonstrated significant inhibitory effects on mycelial growth and spore germination of A. alternata. A greenhouse pot experiment validated the effectiveness of VOCs in disease control, with efficacy reaching 74.84 % after 21 days. Using HS-SPME-GC-MS, twenty VOCs were identified, of which six were evaluated for their antifungal activity against A. alternata. Isovaleric acid showed the most potent antifungal activity, with the lowest EC₅₀ value of 2.22 μL. The antifungal mechanism of isovaleric acid was investigated through morphological and physiological analyses. Isovaleric acid compromised the integrity of the cell wall and membrane of A. alternata, disrupted mitochondrial function, hindered energy metabolism, and diminished antioxidant capacity. Additionally, in vivo experiments revealed that isovaleric acid effectively controlled leaf spot disease, achieving a maximum control efficacy of 77.27 % at an 800-fold dilution. Overall, this study highlights the potential of B. velezensis HC-10 and its VOCs as promising biocontrol agents for managing honeysuckle leaf spot disease.