Gamma-induced Trichoderma guizhouense mutants: enhanced biocontrol of Fusarium wilt in cucumbers and improved environmental stress tolerance

Chemical stress limits Trichoderma biocontrol effectiveness in soil. In 2022–2023, 100 soil samples from cucumber, tomato and eggplant rhizosphere were collected. Using serial dilution method, 24 Trichoderma isolates were obtained. Dual culture method identified the most effective isolate against Fusarium oxysporum f.sp. radicis-cucumerinum . The selected isolate was identified as Trichoderma guizhouense by amplifying the translation elongation factor 1-alpha (tef1-α) and ITS1&4 genes. To enhance the biocontrol potential and tolerance to high electrical conductivity (EC) and potential of hydrogen (pH), spore suspensions of selected isolate were subjected to gamma irradiation using a cobalt-60 source at a dose rate of 0.23 Gy/sec. About 96 mutants of wild type Trichoderma were selected after viability test. The radial growth of Fusarium mycelium was evaluated in dual culture with Trichoderma mutants. Furthermore, Trichoderma mutants were cultured independently on potato dextrose agar (PDA) at different pH and electrical conductivity (EC) levels and incubated for a duration of 72 hours in 27 ^o C and dark. The results showed that the highest and lowest mycelium radial growth of mutants were at pH 7.5, EC 7 and pH 9.5 and EC 9 respectively. The analysis of the Trichoderma mutants over time in the Fusarium competition test, considering EC and pH levels, revealed that certain mutants exhibited significantly greater efficacy than the wild type in suppressing pathogen growth and thriving under high EC and pH conditions. Consequently, the combined application of these mutants may be regarded as appropriate potential biocontrol agents in adverse soil environments.