Biological approach for management of Streptomyces setonii causing common scab of potato

The common scab pathogen was isolated from infected potato tubers and 16S rDNA sequence identified the pathogen as Streptomyces setonii. Three isolates of Pseudomonas fluorescens (Pf1, Pf2 and Pf3), three isolates of Trichoderma harzianum (Th2, Th3 and Th4) and one isolate of Trichoderma asperellum (Th1) were tested for their antagonistic activity against S. setonii both in vitro and in vivo. T. asperellum (Th1) showed tmaximum antibiosis against S. setonii with inhibition zone of 3.50 cm diameter followed by Pf1 isolate of P. fluorescens with inhibition zone of 3.12 cm. Talc based formulations of these two isolates were applied as seed, soil and soil+seed treatment under pot house and field conditions. T. asperellum (Th1) showed maximum reduction in disease severity i.e. 84.65% and 82.58% under pot house and field conditions, respectively. This isolate also acted as biofertilizer by enhancing shoot and root length. The rhizosphere competency showed that the antagonistic microflora competed well and maintained enough population to suppress the disease throughout crop period.