Association of the Hydrolytic Enzyme Chitinase against Rhizoctonia solani in Rhizobacteria-treated Rice Plants

Twenty-two strains of Pseudomonas fluorescens isolated from the rhizosphere soil of nine plant species were screened in vitro for their inhibitory effect on the mycelial growth of the rice sheath blight fungus, Rhizoctonia solani. Of the 22 strains, two promising strains (Pf1 and FP7) were assessed for their effect on seedling vigour and their ability to promote growth in vitro of four cultivars of rice. Both bacterial strains induced systemic resistance in rice cv. IR 50, which is susceptible to sheath blight. After inoculation of the sheaths with the pathogen, Pseudomonas-treated plants showed an increase in chitinase activity significantly higher than that of untreated control plants. A twofold increase in chitinase activity occurred 2 days after inoculation of plants with the pathogen. Western blot analysis of chitinase indicated the expression of 28 and 38 kDa proteins in rice sheaths against R. solani. Increased induction of the pathogenesis-related chitinase isoform in Pseudomonas-treated rice in response to R. solani infection indicates that the induced chitinase has a definite role in suppressing disease development.