Genetics and mapping of neck blast resistance gene s from RIL4 a recombinant inbred line derivative of the broad spectrum resistant genotype Tetep

Abstract

newlineRice blast, caused by the fungus Magnaporthe oryzae, is one of the most destructive diseases newlineworldwide. Compared with leaf blast resistance, our understanding of panicle blast resistance newlineis limited. In this study, we have identified, genetically mapped and physically delimited the newlinechromosomal location of a new neck blast resistance gene from a broad spectrum resistant newlinegenotype RIL4 . The segregation analysis of F2 and F2:3 progenies of cross HPU2216 and newlineRIL4, indicated that the neck blast resistance in RIL4 is controlled by a single dominant gene. newlineThe new gene was tentatively designated as Pb2 . Based on the linkage analysis of 542 newlineindividual susceptible plants, the resistance gene Pb2 was fine mapped to a 1.2 cM region newlineflanked by RM3246 at 0.9 cM on telomeric side and RRS19 at 0.3 cM on the centromeric side newlineof rice chromosome 12. By aligning the sequences of flanking markers on the reference newlinesequence of cv. Nipponbare, a ~6.19 Mb region extending from position 9095272 to newline15287816 b near the centromere of rice chromosome 12 was delineated as the region of neck newlineblast resistance locus. The gene Pb2 was inferred to be embedded in recombination newlinesuppressed region as the average physical/genetic (P/G) distance ratio in this region was ~20- newlinefold higher than the average P/G ratio of 260-280Kb/cM reported for the rice genome. A total newlineof 334 predicted genes were identified in Pb2 region by surveying the equivalent genomic newlineregion of cv. Nipponbare in Rice Annotation Project database (RAP-db) newline(http://rapdbbeta.dna.affrc.go.jp). Five putatively expressed NBS LRR genes were identified newlinein the target region by surveying the equivalent genomic region of Nipponbare and four of newlinethese, NBS-LRR genes Os12g0270300, Os12g0273300, Os12g0281600 and Os12g0438300 newlinewere short-listed as a potential candidate for the resistance gene Pb2. The neck blast newlineresistance gene Pb2 is a novel gene and displays distinct resistance spectrum compared to newlinegenes Pita, Pita2 and Pitr, previously identified from the syntenic region of donor gen