The characterization and antifungal activities of two new Trichoderma antagonistic fungi against four apple disease pathogens

• Two new species of Trichoderma antagonistic fungi were isolated and identified. • The two strains showed antifungal activity against four apple disease pathogens. • The antifungal activity was achieved by the decrease of PG and β-GC activities. Trichoderma is widely utilized in the biological control of plant diseases. In this study, two antagonistic fungi were isolated from cadavers of Spodoptera litura and Mythimna separata , and were identified as Trichoderma afroharzianum and Trichoderma asperelloides . The mycelia of T. afroharzianum grew fastest on the PSA medium under all light conditions, with soluble starch and peptone serving as the optimal carbon and nitrogen sources, respectively. The optimal pH was 6.0 and the lethal temperature was 57°C. The mycelia of T. asperelloides grew fastest on the PDA medium under all light conditions, with maltose and peptone as the optimal carbon and nitrogen sources, respectively. The optimal pH was 5.0 and the lethal temperature was 58°C. The two strains demonstrated antifungal activity against four apple disease pathogens: Alternaria mali , Collectotrichum gloeosporioides , Botryosphaeria dothidea , and Valsa mali . Antagonistic culture results showed that T. afroharzianum achieved an inhibition percentage exceeding 55 % against all four pathogens, while T. asperelloides exhibited the highest antifungal activity against B. dothidea (67.66 %). The mechanisms for controlling apple pathogens were investigated by measuring the activities of Poly Galacturonase (PG) and β-glucosidase (β-GC). In B. dothidea , the activities of PG and β-GC decreased by 58.92 % and 79.54 % when treated with T. afroharzianum culture filtrates, and decreased by 49.28 % and 89.02 % when treated with T. asperelloides culture filtrates, respectively. These results provide valuable information to support the development of T. afroharzianum or T. asperelloides as microbial fungicides for apple diseases.