Volatile Organic Compounds of some Antagonists against Lasiodiplodia theobromae, a Pathogen of Coconut

Abstract

Biocontrol agents are the potential microbes and used for the control of aerial and soil-borne pathogens present in all crops. An attempt was made on identification, morphological and molecular characterization of Lasiodiplodia theobromae, a pathogen causing disease in nuts and leaves of coconut. A virulent isolate Lasiodiplodia theobromae L26 was selected based on the growth parameters and pycnidiospore production. Three efficient biocontrol agents (BCAs) namely Trichoderma asperellum, Bacillus subtilis and Streptomyces rochei, were selected for in vitro studies. Among these, T. asperellum showed a significantly higher percentage of inhibition (81%) in dual culture assay against L26. The inhibition was also confirmed in light microscopic observation, the mycelium of L26 was distorted, lysis of cell wall during the interaction. Volatile organic compounds (VOCs) emitted from BCAs inhibited the fungal growth of L26 by 59.61–47.03% in sealed plate method. Solid-phase microextraction GC-MS analysis revealed numerous new VOCs compounds emitted from the BCAs, whereas the dominant compound was identified as peptaibols, 2,4-di-tert-butylphenol, 2-piperidinone. The strength of peaks of these compounds augmented during the interaction of BCAs with L26, the peak intensity for terpenoids was the predominant class, followed by phenols and heterocyclic organic compound. Crude metabolite (75 μL) of each antagonist tested through agar well method against L26 and showed a complete inhibition. This study demonstrated the ability of BCAs to produce volatile and nonvolatile antifungal compounds, showing that there could a major mechanism involved in and that will be responsible for the successful inhibition of L26 under in vitro. In future combination of these three strains as commercial formulation may be a better management practices for leaf blight and malformation of nuts in coconut