Biological control activity of Trichoderma asperelloides PSU-P1 against gummy stem blight in muskmelon (Cucumis melo)

Abstract

This study aimed to test the antifungal activity of Trichoderma species against gummy stem blight caused by Stagonosporopsis cucurbitacearum in muskmelon plants. Eight isolates of Trichoderma were screened for their inhibitory effect on S. cucurbitacearum, on potato dextrose agar (PDA) by dual culture assay and pre-colonized methods. The results show that Trichoderma sp. PSU-P1 was superior in inhibiting the fungal growth of S. cucurbitacearum. Molecular identification of internal transcribed spacers (ITS), RNA polymerase II (rpb2), and translation elongation factor 1-α (tef1-α) gene sequences revealed the isolate PSU-P1 as Trichoderma asperelloides. To clarify the defense response, enzyme assays of the defense-related enzymes peroxidase (POD) and polyphenol oxidase (PPO) and the cell wall degrading enzymes chitinase and β-1,3-glucanase were conducted for muskmelon seedlings inoculated with T. asperelloides PSU-P1. The results show that the activities of POD, PPO, chitinase and β-1,3-glucanase were higher than in the control. Crude metabolites extracted from T. asperelloides PSU-P1 inoculated muskmelon plants caused abnormal fungal morphology. The inoculation test (in vivo) revealed that muskmelon seedlings treated with T. asperelloides PSU-P1 showed resistance to gummy stem blight with a disease score of 0.2 and disease severity index (DSI) of 10%, lower than those of the control, which had a disease score of 2.8 and 75% DSI. The results obtained in this study reveal that T. asperelloides PSU-P1 exhibited antifungal activity by mycoparasitism and enhanced defense response in muskmelon through the production of defense-related enzymes and cell wall degrading enzymes. High activities of the enzymes are associated with systemic resistance in muskmelon against gummy stem blight.