Indian Phytopath. 67 (3) : 216-221 (2014) Molecular validation for blast and sheath blight resistance in improved rice genotypes and landraces A.K. DUBEY 1 , R.T.P. PANDIAN 1 , H. RAJASHEKARA 1 , A. KHANNA 2 , R.K. ELLUR 2 , P. SHARMA 1 , A. KUMAR 1 , A.K. SINGH 2 , S. GOPALAKRISHNAN 2 , R. RATHOUR 3 and U.D. SINGH 1 * 1 Division of Plant Pathology, 2 Division of Genetics, Indian Agricultural Research Institute, New Delhi 110 012, India 3 Department of Biotechnology, CSK Himachal Pradesh Krishi Viswavidhyalaya, Palampur 176 062, Himachal Pradesh, India ABSTRACT: Globally, two major fungal diseases viz., blast caused by Magnaporthe oryzae and sheath blight incited by Rhizoctonia solani Kuhn. of rice occur in most of the rice-ecosystems resulting in significant yield losses. Host plant resistance is the most eco-friendly management option for combating biotic stresses. In the present study, a set of one hundred rice genotypes were evaluated for blast as well as sheath blight resistance. Twenty seven genotypes were identified to be resistant against M. oryzae isolate (Mo-ni-0066). These genotypes were subjected to molecular validation using the markers linked to major R-genes, viz., Piz5, Pi9, Pita, Pi54, Pi1 and Pib. Individually none of the entries could be observed to possess all these R-genes. However, some of the resistant genotypes were found to possess one or more R-genes. But, evaluation of these genotypes with highly virulent M. oryzae Karnataka isolate (Mo-si-mnd) revealed that only two genotypes viz., Bhusan San and P1490-03 were resistant to blast. Interestingly, molecular validation of these two genotypes did not show any of the above resistance genes, indicating the possible role of some other R-gene/s. When the same set of one hundred rice genotypes were screened for sheath blight resistance, none of the rice genotypes were resistant. However, four genotypes were observed to possess high degree of tolerance to sheath blight and were assessed for the major sheath blight quantitative trait loci qSBR11-1. Key words: Blast, Magnaporthe oryzae, relative lesion height, Rhizoctonia solani, sheath blight RESEARCH ARTICLE *Corresponding author: uds_path@rediffmail.com Rice is one of the most important and widely cultivated food crops in the world. The majority of rice (90 per cent) is being produced in Asian countries with China and India being the major producers. Rice cultivation is often subjected to several biotic stresses. Rice blast and sheath blight are two major diseases of rice which cause significant loss in rice production. Major blast epidemics covering vast area occurs on a regular basis resulting 11 to 30 per cent crop losses annually which represent a yield loss of about 157 million tonnes worldwide (Ahn, 1994). Blast is common in all three ecosystems, irrigated, rainfed uplands and lowlands in which rice is grown. Sheath blight in rice is another important soil-borne fungal disease (Rhizoctonia solani Kuhn.) resulting in dramatic damage to the crop growth causing severe yield losses (Kumar et al., 2009). The estimation of losses due to sheath blight of rice in India has been reported to be upto 54.3 per cent (Chahal, 2005). Wide host range of the pathogen (Rhizoctonia solani Kuhn.) makes the management of sheath blight disease a difficult task. Use of resistant varieties is thought to be one of the most economical and environmentally efficient ways of crop protection in place of chemicals, where the latter generate additional costs in rice production and chemical contamination of environment and food. Though breeding for resistance is the most practical method, it could not be feasible for important diseases due to lack of suitable donors. So far, more than 100 blast resistance genes from japonica (45%), indica (51%) and other (4%) genotypes have been identified (Shikari et al., 2013) and at least 22 blast resistance genes have been isolated through map-based cloning (Pib, Pita, Pi54(Pikh), Pi9, Pid2, Pi2, Piz-t, Pi36, Pi37, Pik-m, Pi5, Pid3, pi21, Pit, Pb1, Pish, Pik, Pik-p, Pia, Pi1 and Pi54rh) (Chen et al., 2014). No rice germplasm in the world has been found to be completely resistant to sheath blight fungus because of the typical quantitative trait of resistance which has been controlled by polygenes (Sha and Zhu, 1989). Quantitative trait loci (QTL) for sheath blight has been identified in rice lines, viz., Tadukan, ZYQ8, LSBR- 2, LSBR-33, Teqing, Jasmine85, Minghui63 and WSS2. Very recently, Channamallikarjuna et al. (2010) have identified major QTLs for sheath blight resistance in traditional rice genotype Tetep. It was found that the sheath blight resistance QTL qSBR11-1 was effective under field conditions across various rice eco-systems. Therefore, molecular markers closely linked to sheath blight resistance QTLs can be used in marker assisted selection. In the present study, a total of 100 rice genotypes have been screened for resistance to blast and sheath blight diseases and the resistant genotypes are evaluated for the presence of major blast resistance genes and QTLs for sheath blight using respective gene linked/ gene based markers. MATERIALS AND METHODS Plant materials A set of 100 rice genotypes including Pusa Basmati-1 (PB-1) as susceptible check and Tetep as resistant check