Abstract

                                Major biotic stresses that affects rice production are sheath blight (ShB) caused by Rhizoctonia solani Kuhn, blast disease caused by fungal pathogen Magnaporthe oryzae and bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae. To reduce the yield loss pyramiding of resistance (R) genes in an elite rice variety is the most effective method. Two high yielding rice varieties namely, ASD16 and ADT43 are extensively grown in South India. These varieties are susceptible to blast, bacterial blight and sheath blight diseases. Hence this study aims to improve these disease susceptible varieties to achieve higher yield in disease prone areas. Improved ASD16 (CB14004) harbouring BB and blast and improved ADT43 (CB14002) harbouring BB resistance genes were used in the present marker assisted backcross breeding program to introgress three sheath blight resistant QTLs (qSBR 11-1, qSBR 11-2 and qSBR 7-1). In every backcross generation, PCR-based markers (RM224, RM209 and RM336), linked with sheath blight resistance QTLs, bacterial blight resistance genes (xa5, xa13 and Xa21) and blast resistance genes (Pi54) were utilized for foreground selection. In addition, a set of forty eight (CB14002 x tetep) and forty one (CB14002) parental polymorphic SSR markers were used for background selection and backcrossing was carried out until BC₃ generation. Background selection studies using polymorphic markers revealed that, an average recovery of 91.15% and the maximum of 92.68% recurrent parent genome in CB14004 x Tetep cross population. In CB14002 x Tetep an average of 90.20% and maximum of 92.70% has been recovered. These plants will be selfed to generate large number of segregating progenies to identify agronomically superior with good grain quality traits and multiple disease resistance lines in rice.

Key Words :Sheath blight, Bacterial blight, Blast, QTLs, R genes, Marker assisted selection, Tetep, CB14002, CB14002