Screening and identification of antagonistic <Emphasis Type="Italic">Streptomyces</Emphasis> spp. against <Emphasis Type="Italic">Clavibacter michiganensis</Emphasis> subsp. <Emphasis Type="Italic">michiganensis</Emphasis> from tomato rhizosphere

The objectives of our present study were to isolate antagonistic Streptomyces from tomato rhizosphere, and evaluate the potential strain for the biological control of bacterial canker of tomato. One hundred and seventy strains of isolated from tomato rhizosphere were tested for antibiosis activity against Clavibacter michiganensis subsp. michiganensis on double-layer agar. Sixty-three isolates showed antibiosis activity with diameter of an inhibition zone ranging from 1.0–6.5 cm. Fifteen Streptomyces strains had strong antibiosis activity against C. m. subsp. michiganensis with diameter of the inhibition zone above 4.0 cm on double-layer agar. Especially, the strain named Z-L-22 showed the strongest antibiosis activity with 6.5 cm inhibition zone. The fermentation filtrate also showed a high inhibition activity against Gram-positive bacteria such as Streptomyces scabies, Staphylococcus aureus, and Bacillus subtilis. Morphological, physiological and biochemical tests combined with 16S rDNA sequence analysis were carried out to identify the strain Z-L-22. Characteristics of the Z-L-22 were similar to those of Streptomyces setonii, and the 16S rDNA sequence showed 99.4% homology to S. setonii. Based on the polyphase taxonomic views, the Z-L-22 was identified as S. setonii.