Abstract
PurposeTo screen endophytic Bacillus producing volatile organic compounds (VOCs) with antifungal activity, and to explore their biocontrol properties toward the growth and pathogenicity of Curvularia lunata.MethodsTwo-sealed-base-plate assays were used to estimate the antifungal activities of Bacillus strains against C. lunata. Conjoint analysis of solid-phase microextraction gas chromatography-mass spectrometry and antagonistic experiments were used to identify the VOCs responsible for the antifungal activity. Effects of individual synthetic VOCs were analyzed along with reactive oxygen species (ROS) accumulation in C. lunata conidia. After exposure to individual VOCs, conidia were also sprayed onto maize leaves to evaluate their pathogenicity. Expression levels of virulence-related genes in C. lunata mycelium following exposure to VOCs were analyzed using quantitative real-time PCR.ResultsAmong the ten endophytic Bacillus strains and two plant growth-promoting rhizobacterial (PGPR) strains, only B. subtilis strain DZSY21 strongly inhibited the growth of C. lunata by producing VOCs. 2-Methylbutyric acid, 2-heptanone, and isopentyl acetate produced by strain DZSY21 showed inhibitory effects on the mycelia growth and conidial sporulation of C. lunata. 2-Heptanone and isopentyl acetate also repressed the germination of conidia and the expression levels of virulence-related genes in C. lunata mycelium. Moreover, isopentyl acetate strongly enhanced the accumulation of intracellular ROS in conidia. The disease indexes of maize leaves sprayed with VOC-treated C. lunata conidia were reduced from 60.52 to 26.64%.ConclusionEndophytic B. subtilis strain DZSY21 displayed the potential to control C. lunata by producing VOCs, especially 2-heptanone and isopentyl acetate.
Highlights
Curvularia lunata is a major pathogen causing leaf spot disease in maize
Screening for bacteria producing volatile organic compounds (VOCs) with antifungal activity Ten endophytic Bacillus strains previously isolated from E. ulmoides as well as two well-known plant growth-promoting rhizobacterial (PGPR) strains
Preliminary screening showed that the VOCs produced by endophytic strains DZSY19 and DZSY21 significantly (P < 0.05) inhibited the growth of C. lunata, and the inhibition rate of DZSY21 (36.2%) was similar to the effect of commercial PGPR strain FZB42 (Fig. 1a)
Summary
Curvularia lunata is a major pathogen causing leaf spot disease in maize. In 1996, the disease expanded over 192,000 hm, leading to 8 million kg yield loss in Liaoning Province, China (Dai et al 1998). Due to variation of pathogen virulence, the disease has (2020) 70:2. It has been shown that some natural compounds can control disease caused by C. lunata. Essential oil of Cymbopogon citratus inhibited conidia germination and reduced disease progress (Mourão 2017), and extracts of Cinnamomum zeylanicum exhibited antifungal activity toward C. lunata (Mishra et al 2009). There is no effective method to control Curvularia spp. It is essential to develop an agent to effectively prevent and control the disease. The application of plant-beneficial microorganisms, which are friendly to the environment and safe for humans, is an alternative to using chemical agents and has attracted increasing attention
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