Biocontrol and Plant Growth-Promoting Potential of Volatile Organic Compound-Producing Endophytic Bacillus safensis and Serratia liquefaciens against Sclerotinia sclerotiorum in Helianthus annuus L

Abstract The present study is aimed at evaluating biocontrol and growth-promoting potential of volatile organic compound (VOC) producing bacterial endophytes against Sclerotinia sclerotiorum in Helianthus annuus L. Two isolates SEB6 and SEB23, exhibiting fungal growth inhibition of 23.75 and 20.0%, respectively, in a dual-plate assay and 76.5 and 35.4%, respectively, in broth were identified by morphological features, biochemical tests, matrix-assisted laser desorption/ionization time of flight mass spectroscopy and 16S rRNA gene sequencing as Bacillus safensis and Serratia liquefaciens. Scanning electron microscopy revealed that fungal growth was inhibited by bacterial antagonists by rupturing, breaking, and shrinking of fungal hyphae. Additionally, the antagonists exhibited phosphate solubilization, and auxins, ammonia, and lipase production. Both strains produced various volatile organic compounds as detected by gas chromatography–mass spectrometry, including 26 VOCs in Bacillus safensis SEB6 and 16 in Serratia liquefaciens SEB23. The compounds 1-docosene, isopropyl myristate, 1,2-benzenedicarboxylic acid, octadecene, diethyl phthalate, glycerin, triacetin, and tetradecane were the common VOCs produced by both the strains. Colonization of plant tissues, as evident by scanning electron microscopy analysis, validated the endophytic nature of both the strains. The pot trial revealed that the combined application of both the strains decreased the disease severity by 88.9% and significantly improved the vigor index, plant growth, total phenol content, and chlorophyll content over control treatment. The maximum increase in N, P, and K contents of 1.73, 0.54, and 6.8%, respectively, was obtained with the treatment BsSEB6 + SlSEB23 in the presence of the fungal pathogen. To the best of our knowledge, this paper for the first time reports the production of 3-pentadecylphenol by the antagonistic Bacillus safensis strain.