Effective assessment of mixed strains against Fusarium oxysporum f. sp. lycopersici causing tomato wilt
Tomato wilt disease, caused by Fusarium oxysporum f. sp. lycopersici , is a major soil-borne disease affecting tomato cultivation. In this study, two strains exhibiting significant control effects on F. oxysporum f. sp. lycopersici and tomato growth-promoting effects were isolated from the rhizosphere. Through physiological and biochemical identification, as well as 16S rRNA identification, these strains were identified as Enterobacter quasihormaechei L33 and Klebsiella oxytoca TL2, respectively. And the two strains of bacteria were confirmed to have no antagonistic effect through antagonistic compatibility tests. Notably, when these strains were mixed in a ratio of 5:1, they demonstrated remarkable antifungal activity. The mixed strains induced mycelium swelling, necrosis, and rupture in F. oxysporum f. sp. lycopersici , resulting in a 56.65 % inhibition of mycelial fresh weight. Additionally, they inhibited spore production with an inhibition rate of 787.5 %, and the inhibition rate of the lipopeptide produced reached 93.80 % at 50 mg/mL. Furthermore, in potting experiments, the mixed strains reduced the disease incidence by 36.25 % after 8 weeks. Additionally, compared to the control group, the mixed bacterial strain group enhanced fresh weight, plant height, chlorophyll a and b levels, and root activities by 96.31 %, 18.51 %, 184.48 %, 53.03 %, and 44.31 %, respectively. In addition, mixed strains can inhibit the cell wall degrading enzymes produced by Fusarium oxysporum f sp., induce plant defense enzymes, including increased activity of peroxidase, catalase, and superoxide dismutase, and reduce the decrease in malondialdehyde levels. The mixed strains could colonize tomato plant roots. Overall, these findings suggest a potential biocontrol agent deriving from the mixed strains against tomato wilt disease.
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