Soil inoculation of Trichoderma asperellum M45a regulates rhizosphere microbes and triggers watermelon resistance to Fusarium wilt

Abstract Fusarium wilt (FW) caused by Fusarium oxysporum f. sp. niveum (FON) is a soil-borne disease that seriously limits watermelon production. In the present study, the Trichoderma asperellum ( T. asperellum ) M45a was shown to be an effective biocontrol agent against Fusarium wilt (FW). In a pot experiment, the application of 10 5 cfu/g of T. asperellum M45a granules had better control effect on FW at the blooming period (up to 67.44%) from soils subjected to five years of continuous cropping with watermelon, while the average length of watermelon vine was also significantly improved(P<0.05). Additionally, the acid phosphatase (ACP), cellulase (CL), catalase (CAT) and sucrase (SC) activities in the M45a-inoculation group were significantly higher than in the control (CK) group, and the soil nutrients (total N, NO3-N, and available P) transformation was significantly increased. Moreover, T. asperellum M45a inoculation reduced fungal diversity and increased bacterial diversity, especially enhancing the relative abundance of PGPR (plant growth promoting rhizobacteria), such as Trichoderma, Sphingomonas , Pseudomonas , Actinomadura and Rhodanobacter . Through functional prediction, the relative abundance of Ectomycorrhizal, Endophyte, Animal pathotroph and saprotroph in fungal community was determined to be significantly lower than observed in the M45a-treated soil. Correlation analysis revealed that Sphingomonas , Pseudomonas and Trichoderma had the most differences in microorganisms abundance, positively correlated with ACP, CL, CAT and SC. These findings will provide ecological fungicide advice for microecological control of FW in continuous cropping watermelon.