Characterization of Streptomyces strains isolated from coffee plantation soils exhibiting plant growth-promoting and antagonistic activity against Fusarium oxysporum f. sp. cubense
Abstract
Fungal diseases continue to cause severe losses in crop production. Among the causal pathogens, Fusarium oxysporum f. sp. cubense (Foc) causes Fusarium wilt, one of the most destructive diseases affecting banana and plantain production worldwide. Its ability to persist in soil for prolonged periods makes disease management and crop re-establishment difficult. The overuse of chemical pesticides has raised environmental and health concerns, creating a need for sustainable biological alternatives for disease management. This study evaluates the potential of Streptomyces strains isolated from coffee plantation soil in Vietnam to antagonize Foc. Although these soils provide a source of actinomycetes, their potential to yield isolates combining antifungal activity with plant growth-promoting traits remains insufficiently studied. Among a total of 30 strains isolated from coffee plantation soil, two strains, HY1.2 and TN72M, were selected for their strong antagonistic properties, exhibiting 74% and 75% inhibition of Foc growth, as well as growth promoting traits, including phosphate solubilization, IAA production, and siderophore synthesis. In particular, HY1.2 and TN72M produced IAA at concentrations of 26.69 and 35.61 µg/mL after 7 days, respectively. Both strains also exhibited phosphate-solubilizing activity with clear zones of 20 mm and 24 mm, while siderophore production reached 8 mm and 15 mm, respectively. In addition, both strains exhibited extracellular enzyme activities, including pectinase, cellulase, and xylanase. Analysis and comparison of the 16S rRNA nucleotide sequences revealed that strains HY1.2 and TN72M are closely related to Streptomyces griseorubens and Streptomyces macrosporeus, respectively. These findings identify coffee plantation soils as a source of Streptomyces isolates combining antagonistic activity against Foc with several traits potentially relevant to plant growth promotion. However, their ability to suppress Fusarium wilt and promote plant growth requires further validation before their agricultural application can be established.