Isolation of indigenous antagonistic microorganism to inhibit Rigidoporus microporus and other plant pathogens and analysis of the bioactive compounds

The objectives of this study were to screen chitinase producing microorganisms to inhibit Rigidoporus microporus (white root rot) and to analyze the bioactive compounds produced by the selected strain using gas chromatography mass spectrometry (GC-MS). A total of 148 microbial isolates were screened from different sources such as composts and soils for chitinolytic activity by colloidal chitin hydrolysis, and then tested for inhibition by dual culture technique. The result showed that 78 isolates exhibited inhibitory activity against R. microporus. Among them, the fungal strain F14 showed the most chitinase production. It was identified as Trichoderma asperellum based on 18S rDNA. T. asperellum F14 was then cultured in 1/5 potato dextrose broth for 28 days to obtain the bioactive compounds using various type of solvents including methanol, n-butanol, ethyl acetate and hexane. Crude ethyl acetate extract displayed the highest inhibitory activity against many plant pathogens such as Agrobacterium tumefaciens, Erwinia carotovora subsp. carotovora, Xanthomonas oryzae, Aspergillus parasiticus, Fusarium culmorum, F. merismoides, F. oxysporum f. sp. gladioli, R. microporus, Verticillium albo-atrum and V. dahliae. The GC-MS analysis of the bioactive compounds produced by T. asperellum F14 showed that they were composed of many known bioactivities. This study indicates that T. asperellum F14 can be used to inhibit white root rot disease and other plant diseases.