KOTASTHANE, ANIL S.ROY, PULI SASANKAPRAKASAM, V.VERULKAR, SATISH BALKRISHNAKHARE, N.CHANDRAKAR, G.2018-08-132018-08-132018http://krishikosh.egranth.ac.in/handle/1/5810064233The present investigation entitled “Defence mechanism in rice against sheath blight caused by Rhizoctonia solani Kühn” were conducted in the laboratory and fields of Department of Plant Pathology, ICAR-Indian Institute of Rice Research, Rajendranagar, Hyderabad, 500030. Rice is a most important cereal and is principle food for about 60% of the world’s population. The production and productivity of rice is reduced by numerous diseases caused by fungi, bacteria, virus, nematodes and other abiotic Title of the thesis “Defence mechanism in rice against sheath blight caused by Rhizoctonia solani Kühn” Full name of the student Puli Sasanka Roy Major subject Plant Pathology Name and Address of Major Advisor Dr. Anil. S. Kothesthane, Head and Professor, Dept. of Plant Pathology, CoA, IGKV, Raipur. Degree to be Awarded M. Sc (Ag) in Plant Pathology Signature of Student Signature of Major Advisor Date: _______________ Signature of Head of the Department xiv constraints. Rice sheath blight caused by Rhizoctonia solani Kuhn [telomorph: Thanetophorous cucumeris (Frank) Donk] is one of the major biotic constraint damaging rice production in India. In the present study, the differential behaviour of R. solani within the different tolerant and susceptible rice plants during different stages of infection. The R. solani hyphal behaviour within the host tissue was distinctly different in the susceptible and tolerant cultivars of rice. The growth of hyphae, formation of infection cushions, density of hyphae on leaf surface and formation of microsclerotia were high on susceptible cultivar when compared with the tolerant one. The correlation between trichomes and susceptibility of the plant was studied. The numbers of trichomes are more (30.76%) on the tolerant cultivar (Whazhuophek) when compared to susceptible cultivar (IR-50). The defence responses of tolerant and susceptible rice were monitored using biochemical analyses and expression analyses of selected defence related genes over a time course during different infection stages. Defence systems were differentially activated in tolerant and susceptible rice plants after inoculation with R. solani and it accounted for the difference in disease severity (PDI) in the those varieties. The pathogen R. solani induced Phenylalanine ammonia lyase (PAL), Superoxide dismutase (SOD), Peroxidase (POX), Polyphenol oxidase (PPO) in tolerant cultivars (Whazhuophek, Ngonolosa and Tetep) whereas in susceptible cultivars (TN-1 and IR-50), it had suppressed POX and SOD enzymes. Distinct difference was observed in activity of these enzymes in different cultivars at different times of course. The enzyme activity was observed peaks at 24 and 48 hours post inoculation mostly in all cultivars. The expression rate of selected defence related genes in two cultivars i.e., Whazhuophek as tolerant and IR-50 as susceptible were studied. The expression transcripts of defence related genes viz., PR-1, PR-2, PR-3, PR-4, PR-5, PR-9, PR-10, PR-13, CHS, LOX, PAL and PPO were studied by using quantitative Real-time PCR (qRT PCR). Results showed that the expression of all genes in tolerant cultivar were higher than that of susceptible cultivar, post inoculation. Significant differences were observed between these two cultivars. These studies suggest that the roles of these defese mechanisms are more significantly related to host-pathogen interaction.ennullThesis