15 Journal of Rice Research 2011, Vol. 4 No 1 & 2 Genetic Studies on Enhanced Disease Reaction of Biparental Progenies (BIPs) to Blast Disease of Rice (Oryza sativa L.) A. Mahalingam 1* , S. Robin 1 and R. Rabindran 2 1 Department of Rice, 2 Department of Plant Pathology, Centre for Plant Protection Studies Tamil Nadu Agricultural University, Coimbatore- 641 003 Abstract The relative effectiveness of intermating or biparental mating in generating superior segregants resistant to blast (Pyricularia grisea ) in rice was studied with JGL 384 x Rasi cross combination. Under this investigation, parental lines (JGL 384, Rasi), 70 F 3 families and 32 intermated progenies (BIPs) were phenotypicaly screened for disease resistance along with checks (TN 1 and IR 50) by sandwich method. The donor parent Rasi was resistant (3.0) and recipient parent JGL 384 (7.0) was susceptible. Among 32 biparental progenies, 22 BIPs were found to be resistant (1.0 and 3.0) and 5 BIPs were moderately resistant to blast and BIPs had a mean score 3.19. In 70 F 3 families nearly 25 per cent were susceptible to blast and have a mean score of 4.02. None of the BIPs families had score 9. It showed that resistance was highly improved in BIPs than their F 3 families. BIPs exhibited superior mean performance than their parents, F 2 and F 3 generation for most of the economically important characters viz., panicle length, number of productive tillers per plant, 1000 grain weight and single plant yield. Most of the intermated progenies were high yielder accompanied by early flowering and resistant to blast disease. Intermating in early segregating generation is an effective approach to generate transgressive segregants with high yielding ability, early flowering and resistance to blast disease by breaking undesirable linkages between yield, grain quality and blast disease. Blast disease of rice caused by the filamentous fungus Magnaporthe grisea has been one of the most damaging diseases of rice and remains most difficult crop diseases to manage (Khush and Jena, 2007). Resistance to blast in ______________________________________________ *Corresponding author: mahalingamcpbg2008@gmail.com Supplementary Tables only in online edition rice is controlled by monogenic dominant, monogenic recessive, two dominant independent genes, two dominant complementary genes or partial resistance controlled by minor genes. Over 80 complete major resistance Pi genes have been described in rice germplasm worldwide (Ballini et al., 2008). To date, Pi- ta, Pi 2 / Piz-t, Pi 5, Pi 9, Pikm, Pi-b, Pi 36, Pi 37, Pi-d 2 , and Pit (Ashikawa et al., 2008; Hayashi and Yoshida, 2009) have been characterized molecularly and their gene structure and resistance functions have been extensively investigated. In spite of the wide distribution of many known genes in rice varieties grown in different countries, genetic studies on blast resistance are limited in tropics. This is partly attributed to the extremely variable nature of blast pathogen, lack of a suitable differential system for the efficient identification of the genes and presence of several resistance genes in indica type varieties may account for the complex nature of genetics of blast resistance (Mackill et al., 1985). However, varieties released as resistant became susceptible after only few seasons or few years of cultivation due to evolution of the pathogen and its adaptation to cultivated resistant varieties. Thus, breeding for disease resistance is a continuous challenge to rice breeders and pathologists. Biparental mating is one of the simplest random mating design available to enforce recombinations and breaking down undesirable linkages as pointed out by Comstock and Robinson (1952). F 2 are the critical generation in rice breeding and they determine the eventual success or failure of hybridization programme (Jennings et al., 1979). Frederickson and Kronstad (1985) stressed that in autogamous crops, intermating among early segregants could open vistas to new levels of genetic variability by breaking up the linkage and genetic recombination within group. The present investigation was carried out with the objective of studying the effectiveness of biparental mating on releasing superior transgressive segregants with high yield and blast resistance.