Dual role of Trichoderma koningiopsis T-51 in promoting watermelon growth and controlling Fusarium wilt disease in continuous-cropping fields

The increasing difficulty of controlling watermelon Fusarium wilt disease (caused by Fusarium oxysporum f. sp. niveum, Fon) in continuous-cropping systems using traditional chemical control techniques highlights the need for sustainable alternative strategies. This study evaluated the biocontrol agent Trichoderma koningiopsis T-51 through controlled assays and multi-year field trials between 2020 and 2024 at multiple sites in Shanghai, China. T-51 exhibited the most effective activity in susceptible genotypes, reducing the disease index by 76.5% in the susceptible watermelon line W4k-1 in controlled assays. Field trials revealed dose-dependent effects, with treatment using T-51 at high concentrations (5×10⁷ CFU/mL, repeated drenching) reducing disease incidence by 59 to 76% in continuous-cropping fields. In contrast, low concentrations (5×10⁶ CFU/mL) advanced flowering by 6 days and increased average fruit number per plant by 15 to 20%. Marketable fruit yields increased by 15 to 18% in T-51–treated plots without compromising fruit quality during continuous cropping in large fields. T-51 stably colonized soil and reshaped soil microbiomes, suppressing Fusarium populations, and enriching potentially beneficial bacteria (Bacillus and Pseudomonas) in continuous-cropping fields. The broad fungicide compatibility of T-51 treatment indicates that it could be used in combination with fungicides. Overall, T-51 proves to be an effective and sustainable tool for integrated management of watermelon Fusarium wilt, particularly for high-yield, disease-susceptible cultivars, and offers a sustainable alternative to chemically intensive practices.