Multicomponent coordinated defence response of rice to Rhizoctonia solani causing sheath blight

An excellent multicomponent coordinated defence response of rice plants (cv. IET-2233) to fungal attack has been, demonstrated and a plausible relationship among them has been proposed. Some selected defence;components such as momilactone 'A' (a rice phytoalexin), beta-1,3-glucanases and exo chitinases (both pathogenesis related (PR)-proteins) and an enzyme phenylalanine ammonia lyase (PAL) were employed as biochemical parameters for evaluating the degree of-response of rice plants to Rhizoctonia solani Kuhn, a fungus causing sheath blight disease. A systemic fungicide kitazin which reduced disease significantly also concomitantly activated biosynthesis of momilactone A, induced PR-proteins and increased PAL activity in rice. Treatment of rice leaf sheaths with a PR-protein inhibitor (kinetin + NAA) increased disease markedly but inhibited beta-1,3-glucanases and exo-chitinase activities in treated plants. Similarly; amino oxyacetic acid (AOA), a PAL inhibitor also enhanced disease intensity and inhibited PAL activity in treated, inoculated plants. Results confirm the coordinated function of various defence components in rife following infection by Rhizoctonia and also after abiotic induction of resistance.