GENETICS AND MAPPING RESISTANCE GENE(S) F INBRED LINE DERIVATI RESISTANT GENOTYPE CHAUDHARY SARWAN KUMAR HIMACHAL PRADESH KRISHI VISHVAVIDYALAYA PALAMPUR Partial fulfilment of the requirements for the degree DOCTOR OF PHILOSOPHY (DEPARTMENT OF (AGRICULTURAL BIOTECHNOLOGY) OF NECK BLAST FROM RIL4 - A RECOMBINANT DERIVATIVE OF THE BROAD SPECTRUM ‘Tetep’
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Date
2019-01-02
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CSKHPKV, Palampur
Abstract
Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most destructive diseases
worldwide. Compared with leaf blast resistance, our understanding of panicle blast resistance
is limited. In this study, we have identified, genetically mapped and physically delimited the
chromosomal location of a new neck blast resistance gene from a broad spectrum resistant
genotype ‘RIL4’. The segregation analysis of F2 and F2:3 progenies of cross HPU2216 and
RIL4, indicated that the neck blast resistance in RIL4 is controlled by a single dominant gene.
The new gene was tentatively designated as ‘Pb2’. Based on the linkage analysis of 542
individual susceptible plants, the resistance gene Pb2 was fine mapped to a 1.2 cM region
flanked by RM3246 at 0.9 cM on telomeric side and RRS19 at 0.3 cM on the centromeric side
of rice chromosome 12. By aligning the sequences of flanking markers on the reference
sequence of cv. Nipponbare, a ~6.19 Mb region extending from position 9095272 to
15287816 b near the centromere of rice chromosome 12 was delineated as the region of neck
blast resistance locus. The gene Pb2 was inferred to be embedded in recombination
suppressed region as the average physical/genetic (P/G) distance ratio in this region was ~20-
fold higher than the average P/G ratio of 260-280Kb/cM reported for the rice genome. A total
of 334 predicted genes were identified in Pb2 region by surveying the equivalent genomic
region of cv. Nipponbare in Rice Annotation Project database (RAP-db)
(http://rapdbbeta.dna.affrc.go.jp). Five putatively expressed NBS–LRR genes were identified
in the target region by surveying the equivalent genomic region of Nipponbare and four of
these, NBS-LRR genes Os12g0270300, Os12g0273300, Os12g0281600 and Os12g0438300
were short-listed as a potential candidate for the resistance gene Pb2. The neck blast
resistance gene ‘Pb2’ is a novel gene and displays distinct resistance spectrum compared to
genes Pita, Pita2 and Pitr, previously identified from the syntenic region of donor genotype
Tetep. The ‘Pb2’ linked markers identified during this study can be exploited in markerassisted
breeding programmes for its speedy and precise mobilization into blast susceptible
varieties.
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