BIOLOGICAL-CONTROL OF RHIZOCTONIA SP ROOT-ROT OF CASUARINA-EQUISETIFOLIA SEEDLINGS BY FRANKIA SPP STRAINS

Seventy Frankia spp. strains (nodulating N-2-fixing actinomycetes) wer e isolated from root nodules of Casuarina equisetifolia from different localities of Tamil Nadu state, India. From these, four strains (UMCe 12, UMCe23, UMCe35, and UMce55) were selected. Their potential use as biological control agents for Rhizoctonia solani root rot disease of C . equisetifolia seedlings and their relative efficiency in nodule prod uction were investigated. Between the two inoculum broadcast systems t ested, seed-coating with Frankia spp. cell suspension was superior to the soil application of cells as sand-vermiculite-basal ammonium propi onate inoculum. UMCe12 was the promising strain, offering the highest level of disease protection (81.1%) and nodule production (88.1%) in t he R. solani-infested soil, followed by UMCe23 (60.3 and 65.5% of dise ase protection and nodule production, respectively), UMCe55 (53.5 and 58.2%), and UMCe35 (45.4 and 44.5%). Further, a significant positive c orrelation was observed between the dose of Frankia spp. and efficienc y in both disease control and nodule production.