CHARACTERIZATION OF STREPTOMYCES SAMPSONII STRAIN C4 FOR THE DEVELOPMENT OF AN EFFECTIVE MICROBIAL CONSORTIUM FOR LEGUMINOUS PLANT PROTECTION

Streptomyces is the most abundant genus of Actinobacteria, including several species used by the pharmaceutical industry for the production of antibiotics. Many Streptomyces strains have also been reported as effective plant growth promoters and biocontrol agents, and can be considered useful for agricultural applications. A colony morphologically attributable to Actinobacteria was isolated from a compost tea and identified as Streptomyces sampsonii by 16S rDNA gene sequencing. This strain, named C4, was able to form biofilm and to produce indole-3-acetic acid. Additionally, it showed a marked antagonistic activity against the phytopathogenic fungi Botrytis cinerea, Fusarium solani, and Macrophomina phaseolina in in vitro dual test. Strain C4 also produced active volatile compounds against B. cinerea, producing a significant reduction in the colony size. Moreover, the cultural filtrate of C4 inhibited the conidia germination of B. cinerea. The biocontrol activity of C4 against the three phytopathogenic fungi was evaluated in vitro on tomato detached leaves. In vivo biostimulation and biocontrol activities of C4 were investigated on chickpea and pea plants with the aim of including this strain in a microbial mixture to be used for the protection of the two leguminous crops. Compatibility of C4 with the other strains of the mixture, namely Bacillus thuringiensis, Bacillus halotolerans, and Pseudomonas putida, was preliminarily evaluated.