Effects of chitin and salicylic acid on biological control activity of Pseudomonas spp. against damping off of pepper

Fluorescent pseudomonads (SE21 and RD41) and resistance inducers (chitin and salicylic acid) were examined for plant growth promotion and biological control of damping off of pepper caused by Rhizoctonia solani. The antagonists SE21 and RD41 isolated from the rhizosphere of pepper were found to be effective in inhibiting the mycelial growth of R. solani in a dual culture assay and increasing the seedling vigour in a roll towel assay. Both antagonists were further characterized for biocontrol and plant growth promoting features. The addition of inducers (chitin alone) increased the antagonist's population in the culture medium. In a further study, seed treatment with antagonists showed an increase in plant growth and controlled the damping off under in vivo conditions. Amendment with inducers alone showed a moderate degree of plant protection against R. solani. However, the reduction in disease was more pronounced when inducers were applied with antagonists. Amendment with chitin alone enhanced biocontrol efficiency of both SE21 and RD41. However, amendment with SA alone or in conjunction with chitin showed a moderate effect on biocontrol efficiency of the antagonists. These results show that the biocontrol efficiency of antagonists SE21 and RD41 may be stimulated by chitin resulting in a significant increase in their population density and antagonistic effect against R. solani.