Biocontrol of Colletotrichum falcatum with volatile metabolites produced by endophytic bacteria and profiling VOCs by he
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RESEARCH ARTICLE
Biocontrol of Colletotrichum falcatum with volatile metabolites produced by endophytic bacteria and profiling VOCs by headspace SPME coupled with GC–MS V. Jayakumar1
•
A. Ramesh Sundar1 • R. Viswanathan1
Received: 17 June 2020 / Accepted: 4 September 2020 Ó Society for Sugar Research & Promotion 2020
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
& V. Jayakumar [email protected] 1
Plant Pathology Section, Division of Crop Protection, ICARSugarcane Breeding Institute, Coimbatore 641007, Tamil Nadu, India
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. Keywords Sugarcane Endophytic bacteria Red rot Biocontrol VOCs SPME GC–MS
Introduction Red rot caused by Colletotrichum falcatum Went. is regarded as disease of major importance in all the sugarcane growing countries (Chona 1980; Singh 2008). In India, red rot was first noticed in Godavari delta of Madras province (Barber 1901) after that a series of epidemics were reported in many parts of country (Chona and Padwick 1942; Satyavir 2003; Viswanathan and Samiyappan
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