Gamma Irradiation Enhances the In Vitro Biocontrol Potential of Trichoderma Species Against Major Rice Pathogens Rhizoctonia solani and Pyricularia oryzae

Improving the efficacy of microbial biocontrol agents is a pivotal strategy for sustainable management of rice blast and sheath blight caused by Pyricularia oryzae and Rhizoctonia solani, respectively, in Vietnam. In this study, Trichoderma sp. TVN-A0 and Trichoderma sp. TVN-H0 were irradiated by gamma to generate mutants for screening the enhanced antagonistic activity against P. oryzae and R. solani. The potential mutants were screened by antifungal metabolite production via the cellophane membrane assay (ICM), antagonistic performance through dual culture confrontation assays (IDC), volatile organic compound bioassays (IVOCs), and chitinase activity. As a result, among five potential mutants derived from each wild-type strain (AM1-AM5 and HM1-HM5), mutant AM2 originated from TVN-A0, and mutant HM2 derived from TVN-H0 demonstrated the highest inhibition rates and chitinase activities. The AM2 exhibited ICM of 96.71% against R. solani, 92.57% against P. oryzae, IDC of 87.76%, and IVOCs of 83.57%, while HM2 possessed ICM of 95.33% against R. solani, 85.28% against P. oryzae, IDC of 91.24%, and IVOCs of 79.33%. The genetic differences among mutants and their parents were investigated by RAPD. The non-GMO AM2 and HM2 mutants are promising candidates for biocontrol of the diseases caused by P. oryzae and R. solani in Vietnam.