Biocontrol of Colletotrichum falcatum with volatile metabolites produced by endophytic bacteria and profiling VOCs by headspace SPME coupled with GC–MS

Abstract

A total of 49 endophytic bacteria isolated from sugarcane were screened in vitro for antagonistic property against C. falcatum through production of volatile organic compounds (VOCs). Among them, 27 bacteria produced volatiles with moderate inhibitory level, i.e. 30 to 50% and 9 produced volatiles with strong inhibitory properties, i.e. > 50% mycelial growth inhibition over control. The volatile compounds produced by B. axarquiensis—ESR 7 inhibited C. falcatum mycelia growth to the tune of 59.2% followed by B. licheniformis—ESR 26 (57.8%) and B. subtilis—ESR 24 (54.8%), respectively. The volatiles produced by bacteria not only inhibited the radial growth of mycelium but also suppressed the vertical expansion of mycelia and caused deformation in mycelia growth. The VOCs produced by 24 endophytic bacteria completely inhibited spore formation in C. falcatum culture. Profiling of antagonistic VOCs produced by bacterial strains ESR 7, ESR 24 and ESR 26 was done by head space-solid phase microextraction (SPME) coupled with gas chromatography mass spectral analysis. The analysis showed the presence of 63 compounds belonging to chemical groups of alcohols, esters, hydrocarbons, ketones, acids, amino acid, carbohydrates, ethers, aldehydes, amines and amides. Among the identified microbial volatiles, 6 compounds viz., acetic acid, methoxy-phenyl-oxime, octamethyl-cyclotetrasiloxane, 5,7-dimethyl-undecane, hexamethyl-cyclotrisiloxane and dodecane were reported in VOCs produced by all three bacteria. However, among 63 volatiles, only 31 were already reported to be produced by many bacteria and fungi and 11 compounds viz., acetic acid, hexanal, 2-ethyl-1-hexanol, undecane 5,7-dimethyl, undecane 3,7-dimethyl, 2-decanone, dodecane, 2-undecanone, 2-dodecanone, 1,2-Benzenedicarboxylic acid, diisooctyl ester and 2-methyl-hexadecanol were reported with antagonistic property against many plant pathogens. The study revealed that many VOCs produced by B. axarquiensis—ESR 7, B. subtilis—ESR 24 and B. licheniformis—ESR 26 play role in mediating antagonism against C. falcatum.