Antifungal and plant growth-promoting activities of Streptomyces roseoflavus strain NKZ-259

Biocontrol approach, using beneficial microorganisms, is becoming an important alternative to the use of chemical fungicides to control crop diseases. Therefore there is a need to found new effective biocontrol agents. Herein, a bacterial strain named NKZ-259 was isolated from soil samples obtained from Qilian Mountain, Qinghai, using the dilution plate method and streak plate technique. Strain NKZ-259 was identified as Streptomyces roseoflavus based on 16S rDNA sequencing, which displayed high antagonistic activity against six fungal pathogens tested. A greenhouse experiment showed that the use of NKZ-259 fermentation broth reduced the incidence of the tomato gray mold by 66.67%, and promoted the growth of tomato and pepper seedlings, with a significant increase in plant height, root length, and fresh weight compared to controls; the field experiment also showed the growth promotion of tomato and pepper seedlings by the use of NKZ-259 fermentation broth. Furthermore, indoleacetic acid (IAA) production was also detected in strain NKZ-259 using the Salkowski's reagent method, and was important for its plant growth-promoting effects. The results suggest that NKZ-259 has potential for commercial application as a biofertilizer or biocontrol agent.