A Streptomyces sp. strain: Isolation, identification, and potential as a biocontrol agent against soilborne diseases of tomato plants

Continuous cropping of tomato plants leads to the prevalence of soilborne diseases, such as Fusarium wilt and bacterial wilt. Actinobacteria are gaining interest in agriculture as biological control agents (BCAs). In this study, we isolated an actinomycete strain, FJAT-31547, from the rhizosphere soil of a healthy tomato plant in a serious soilborne diseased field. The strain FJAT-31547 exhibited broad-spectrum antifungal and antibacterial activities against 6 species of phytopathogenic fungi and 7 species of phytopathogenic bacteria, especially Fusarium oxysporum and Ralstonia solanacearum. Based on morphological and physiological characteristics and 99.64% of 16S rRNA gene sequence similarity with Streptomyces diastaticus subsp. ardesiacus, the strain was identified as a member of the genus Streptomyces. Thirteen chemical compounds with a high match degree (more than 90%) were identified in the crude extracts of Streptomyces sp. by gas chromatography-mass spectrometry (GC-MS) analysis, and n-hexadecanoic acid was the major constituent. The crude extract of strain FJAT-31547 exhibited the minimum inhibitory concentration (MIC) against F. oxysporum and R. solanacearum with 6.250 mu g mL(-1) and 3.125 mu g mL(-1), respectively. Pot experiments showed that after preinoculation with the strain FJAT-31547, the disease incidence of tomato plants was reduced by 80.59% for Fusarium wilt and 76.92% for bacterial wilt. Moreover, the strain FJAT-31547 had a growth promoting effect on tomato plants, increasing root length, plant height and stem diameter by 16.62%, 15.01% and 21.13%, respectively. Together, the Streptomyces sp. strain FJAT-31547 could be used as BCA against tomato Fusarium wilt and bacterial wilt.