Studies on the development of hexaconazole-tolerant <i>Trichoderma asperellum</i>

The generation of fungicide-tolerant Trichoderma strains is desirable for managing crop plant diseases during severe disease outbreaks as fungicides immediately suppress the fungal pathogens, and a fungicide-tolerant Trichoderma strain later suppresses the weakened pathogens caused due to fungicide exposure for a prolonged period of crop growth. Thus, in the present study, hexaconazole-tolerant T. asperellum was generated by induced mutagenesis using ethyl methyl sulfonate. Four hexaconazole-tolerant strains that did not show any growth defects were selected. Among them, two hexaconazole-tolerant strains, namely, T. asperellum strains T7 and T18, showed a threefold increased tolerance compared to their parental strain. Hexaconazole-tolerant T. asperellum strain 18 exhibited the maximum mycelial growth inhibition of Macrophomina phaseolina and improved black gram seed germination and vigour index compared to its parental strain. Further black gram’s dry root rot disease incidence was effectively suppressed with the application of 0.01% hexaconazole. Thus, this study indicates that the combined application of hexaconazole-tolerant strains and the reduced dose of hexaconazole effectively suppressed black gram’s dry root rot disease.