Genetic analysis of resistance to rice bacterial blight in Uganda

Abstract

Rice bacterial blight ( Xanthomonas oryzae pv. oryzae ) is a major\nconstraint to rice ( Oryza sativa L.) production in Uganda and as\npart of strategies to develop resistant cultivars, it is important to\nevaluate resistance of commonly used cultivars. A full-diallel mating\ndesign involving three resistant and three susceptible rice cultivars\nwas used to produce F1 and F2 progenies in a screen-house at the\nNational Crop Resources Research Institute (NaCRRI), Namulonge in\nUganda. The parents and F2 populations were challenged with the ≤\nXanthomonas oryzae pv. oryzae isolate (UX00) and lesion lengths were\nscored 21 days after inoculation (DAI). Griffing’s combining\nability analysis showed significant specific combining ability (SCA)\nand non-significant general combining ability (GCA) effects, indicating\nthe preponderance of non-additive gene effects in controlling the\nresistance to bacterial leaf blight (BLB) in rice. Rice genotypes,\nNERICA14, NERICA10 and NERICA4 had desirable GCA estimates, and were,\ntherefore, the best general combiners. Crosses CO39 x NERICA10 and\nNERICA14 x IRAT104 had favorable SCA values. These hybrids are thus,\npromising in developing the BLB resistant progenies. Significant\nreciprocal effects indicate the importance of maternal contribution in\ncontrolling the BLB virulence. For this, resistant lines can be used as\nfemale parents for fear of affecting transfer of resistance to the\nprogenies, and the hybrids and their reciprocals would be handled\nseparately. Low estimates of narrow sense coefficient of genetic\ndetermination (NSCGD) (0.9%) and medium broad sense coefficient of\ngenetic determination (BSCGD) estimates (16.4%) highlight the influence\nof non-additive gene action in controlling the resistance to BLB,\nconfirming an effective selection of superior genotypes at advanced\ngenerations when the maximum homozygosity is fixed.