In-vitro Efficacy of Trichoderma asperellum against wilt in Watermelon Caused by Fusarium oxysporum f. sp. niveum

The production of watermelon (Citrullus lanatus) in India is negatively impacted by Fusarium oxysporum f. sp. niveum (Fon) which is a major soil-borne disease. Keeping Fusarium wilt under control is crucial for maintaining crop yield. Various approaches have been proposed to combat Fusarium wilt. The toxic forms of chemicals remain in the soil and pollute the entire environment because they are continuously used. The purpose of this study is to determine the occurrence and severity of Fusarium wilt in important districts where watermelon is grown in Tamil Nadu and to evaluate the in vitro efficacy of native Trichoderma asperellum isolates as potential biocontrol agents. Field surveys conducted across 15 locations revealed varying levels of disease incidence, with Vaidapakkam village recording the highest incidence (42.14%). Ten Fon isolates (Fon1–Fon10) and ten native Trichoderma isolates (TsI1–TsI10) were obtained from infected plant tissues and rhizosphere soils, respectively. Among these, Fon5 was identified as the most virulent isolate. Dual culture assays demonstrated that T. asperellum isolate TsI4 exhibited the highest antagonistic activity, inhibiting Fon5 growth by 81.74%. Further, poisoned food and well diffusion assays confirmed that TsI4 culture filtrates significantly suppressed Fon5 mycelial growth in a dose-dependent manner, achieving up to 95.13% inhibition in the poisoned food assay and a 28.72 mm inhibition zone in the agar well diffusion method at 40% concentration. The results indicate that T. asperellum isolates, particularly TsI4, have a strong chance of being biological control agents against Fusarium wilt in watermelon cultivation, and are an ecological alternative to chemical fungicides. Trichoderma asperellum shows good effect on suppression of Fusarium wilt pathogen under in vitro condition. Farmers growing watermelon crop must use Bio-control agent Trichoderma for the management of wilt disease thereby resulting in sustainable yields with highest economic returns.