Abstract
Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) is globally one of the most destructive soil-borne fungal diseases. Biological control using environmental microorganisms is considered as an alternative and sustainable strategy. Actinomycetes have the potential to explore biocontrol agents due to their production of diverse metabolites. The isolation and identification of high-efficiency and broad-spectrum antagonistic actinomycetes are the key for the application of biocontrol agents. In the present study, 60 actinomycetes were obtained from the rhizosphere soil of Machilus pingii in the primitive ecological natural reserve of Hainan province, China. Seventeen isolates and their extracts exhibited significant antifungal activity against F. oxysporum TR4. Particularly, strain BITDG-11 with the strongest inhibition ability had a broad-spectrum antifungal activity. The assay of its physiological and biochemical profiles showed that strain BITDG-11 had the ability to produce IAA and siderophores and had a positive response to gelatin liquefaction and nitrate reduction. Enzyme activities of chitinase, β-1,3-glucanase, lipase, and urease were also detected. Average nucleotide identity calculated by comparison with the standard strain genome of Streptomyces albospinus JCM3399 was 86.55% below the novel species threshold, suggesting that the strain could be a novel species. In addition, Streptomyces BITDG-11 obviously reduced the disease index of banana plantlets and promoted plant growth at 45 days post inoculation. The higher and lasting expression levels of defense genes and activities of antioxidant enzymes were induced in the roots of banana. Genome sequencing revealed that the Streptomyces BITDG-11 chromosome contained large numbers of conserved biosynthesis gene clusters encoding terpenes, non-ribosomal peptides, polyketides, siderophores, and ectoines. Fifteen bioactive secondary metabolites were further identified from Streptomyces BITDG-11 extract by gas chromatography–mass spectrometry. Dibutyl phthalate demonstrating a strong antifungal activity was the major compound with the highest peak area. Hence, Streptomyces sp. BITDG-11 has a great potential to become an essential constituent of modern agricultural practice as biofertilizers and biocontrol agents.
Highlights
Banana (Musa spp.) is one of the world’s most important staple and cash crops and widely cultivated in 135 countries in tropical and subtropical regions
A total of 60 actinomycetes were isolated from the rhizosphere soil of M. pingii using four culture media of humic acid–vitamin (HV) (18), glucose–aspartic acid (GA) (12), starch casein agar (SCA) (10), and Gause’s No 1 (20)
The results showed that different temperatures reduced antifungal activity of the extract against F. oxysporum tropical race 4 (TR4), but 57.05% was kept after treatments at 121◦C for 1 h (Figure 4A)
Summary
Banana (Musa spp.) is one of the world’s most important staple and cash crops and widely cultivated in 135 countries in tropical and subtropical regions. Annual banana production in the world is estimated at over 145 million tons (Ploetz, 2015a). Fusarium wilt of banana caused by Fusarium oxysporum f. Cubense is one of the most destructive soil-borne fungal diseases and seriously threatens the global banana industry. The causal agents are subdivided into four races based on the banana cultivars infected (Dita et al, 2018). F. oxysporum tropical race 4 (TR4) distributed in the main producing areas globally can infect almost all banana cultivars (Pegg et al, 2019). It can be spread by banana material, soil and machinery, irrigation water, etc. It can be spread by banana material, soil and machinery, irrigation water, etc. (Ploetz, 2015b)
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