Evaluation of Indigenous Trichoderma Isolates from Nepal Terai Region against Sheath Blight Disease of Rice

Abstract

Sheath blight caused by Rhizoctonia solani is a major constraint to rice production in Terai region of Nepal, often resulting in substantial yield losses. The heavy use of chemical fungicides raises serious concerns about environmental pollution and human health, highlighting the need for safer disease management options. In this context, biological control using Trichoderma spp. has gained considerable attention. This study aimed to manage sheath blight in spring rice using indigenous Trichoderma spp. Based on prior in vitro and screenhouse experiments, three promising Trichoderma isolates and a virulent isolate of R. solani were selected for field evaluations. Four rice varieties, Hardinath-1, Chaite-2, BINA Dhan and Chaite-5 were included in the experiment. Rice seeds were soaked in Trichoderma spore suspension (10⁶ spores/ml) and sown in nursery beds. Twenty-five days old seedlings were root-dipped in Trichoderma spore suspension before transplanting and a foliar spray was applied 24 hours after pathogen inoculation. Among the tested isolates, Trichoderma isolate RN-12 was found to be highly effective, reducing the average lesion size by 75.1%. Plants treated with RN-12 showed a significant reduction in disease severity, and lower relative lesion height compared to untreated control. These results clearly demonstrated the strong antagonistic potential of RN-12 in limiting both the development and progression of sheath blight. In addition to disease suppression, RN-12 also enhanced plant growth. The highest values for total tiller number, flag leaf length, panicle length, and total grains per panicle were consistently recorded in RN-12-tretaed plants across all four rice varieties, showing its superiority over other treatments, including untreated control.