Characteristics of endophytic bacteria Sz-2 from smooth vetch (Vicia villosa var.) and its control effect on banana Fusarium wilt

Objectives From the roots of Vicia villosa var., a main green manure cultivar, we screened out endophytic bacteria strain (Sz-2) with pro-biotic and antagonistic effects on banana Fusarium wilt, and studied their characteristics to enrich the resource pool of biocontrol and pro-biotic strains.

Methods The inhibitory effect of the strain Sz-2 was determined using the plate standoff test, and the in vitro phosphorus solubilizing, potassium solubilizing, nitrogen fixing, and iron-producing carrier capacity were also determined using regular methods. The strain was taxonomically identified by morphological observations, physiological and biochemical determinations, and 16S rDNA sequence analyses. The morbidity indices of banana leaf and bulb, as well as the promotional effect of the strain were tested using a pot experiment, in which four treatments (CK, TR4, Sz-2+TR4, and Sz-2) were set up to assess the efficacy of the strain in the prevention and control of banana blight, and the promotion effect on the growth of bananas.

Results Strain Sz-2 showed a good antagonistic effect on Fusarium oxysporum f. sp. cubense, with a plate radial inhibition rate of 74.3%. Strain Sz-2 is a Gram-negative bacterium, with light white, radial colony morphology, positive for contact enzyme, oxidase, lysine decarboxylase, β-galactosidase, arginine bis-hydrolyase, gelatin hydrolysis, nitrate reduction reaction, cellobiose, citric acid reaction, glucose fermentation reaction, and tyrosine hydrolysis, and negative for indole reaction, starch hydrolysis, H₂S-producing reaction, ornithine decarboxylase, and urease reaction. Combining the morphology and molecular biology, strain Sz-2 is identified as Stenotrophomonas maltophilia. In the pot experiment, the inoculation of Sz-2 decreased the banana bulb and leaf blight index by 69.66% and 84.60%, respectively; the longitudinal section of the bulb and the leaf color were normal and the plants were healthy under treatment of Sz-2; the stem thickness, the single plant fresh weight and height were 6.01 mm, 83.3 g and 11.82 cm higher than CK.

Conclusions Strain Sz-2 has obvious antagonist on banana Fusarium wilt disease and promotion effect on the growth of banana due to its phosphorus and potassium solubilization and iron-producing carrier function. Considering the original green manure to carry the strain, functional green fertilizers could be developed for banana in the future.