A quantitative trait locus (QTL) analysis was carried out with a recombinant inbred line (RIL) population to identify the chromosomal regions responsible for cold tolerance of rice (Oryza sativa L.). The RIL population, consisting of 80 lines, was developed from a cross between the indica cultivar, Milyang 23 and the japonica weedy rice, Hapcheonaengmi 3. The population was genotyped with 2 morphological and 132 DNA markers, providing an average interval size of 11.3 cM, and was also evaluated for traits related to agricultural performance in cold water and in control plots. The RILs showed delayed heading and reduced culm length in the cold water plot and the differences in heading date and culm length between two plots were statistically significant. Cold tolerance was measured as days to heading, culm length, spikelet fertility, leaf discoloration, and panicle exsertion in the cold water plot, and difference in days to heading and the reduction ratio of culm length between two plots. A total of 14 QTLs for 7 traits were identified using single point and composite interval analysis. The number of QTLs per trait ranged from one to three. Phenotypic variation associated with each QTL ranged from 5.8 to 32.8 %. No digenic interaction was detected. Several QTLs associated with cold tolerance were clustered in a few chromosomal blocks. For 11 (78.6 %) of the QTLs identified in this study, the Hapcheonaengmi 3-derived alleles contributed desirable effects and favorable alleles were detected for difference in days to heading, spikelet fertility, panicle exsertion and leaf discoloration. From this study, it can be concluded that weedy rice is useful as a source of valuable alleles for breeding cold tolerance in rice.
The nearly isogenic nature of the introgression lines (ILs) provides a relative advantage over other segregating populations in the rapid implementation of pyramiding approach through crosses and marker analysis. A set of 126 ILs carrying various introgressed segments from a presumed wild progenitor, Oryza rufipogon Griff. Acc. W1944 in the background of an elite Korea japonica cultivar (O. sativa L.), Hwayeongbyeo, was constructed using the marker assisted selection (MAS) technique combined with repeated backcrosses. The 126 ILs have different W1944 segments on each chromosome, with 100% coverage of wild segments on chromosome 1, while for chromosome 10, the coverage was only 33.3%. The mean number of homozygous and heterozygous donor segments were 3 (ranging from 0 to 7) and 4.7 (ranging from 1 to 14.5), respectively, and 31.6% of introgressed segments had sizes of less than 10.5 cM. A total of 41 quantitative trait loci (QTLs) and two loci associated with pericarp coloration were identified. The number of QTLs per trait ranged from 2 to 6. Phenotypic variance associated with each QTL varied from 9.1 to 52.2%, with an average of 17.1%. For 11 (26.8%) of the QTLs detected in this study, the O. rufipogon-derived alleles contributed the desired agronomic effect despite the overall inferior characteristics of the wild phenotype. Favorable alleles from the O. rufipogon accession were identified for panicle number, panicle length, days to heading, secondary branches, spikelets per panicle, and 1,000-grain weight.
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