Field experiments were conducted to investigate persistence of Chinese milk vetch(CMV) seed under naturally reseeded CMV-rice cropping systems during the period of 2007～2009. Persistence of the CMV seeds were evaluated in the naturally reseeded CMV-rice field on different tillage methods and soil depths based on the seed number recovered and the seed longevity in soil. Field observation in the naturally reseeded CMV rice field showed that as many as 917～2,185 CMV seeds m-2 were found from 0～15cm soil depth in the rotary tillage and 250～10,105 CMV seeds in minimum tillage rice cultivation in autumn. The recovered seed germinated 25～33%, 23～43% but still had high percentage of hard seed having 64～72% and 51～77%. Field experiment showed that the CMV seedling still emerged even after 2 years of continuous destructive killing of emerged CMV plant by rotary tillage in naturally reseeded CMV-rice field, indicating that CMV seeds persistent at least two years in rice field.

Cold sensitivity has been shown to vary and the cold tolerance from vegetative to reproductive stage appears to be independent during the life cycle. In the current study, cold tolerance under high elevation rice growing area were evaluated using F4 generation of 181 lines derived from Gayabyeo*2/Chhamrong. Five main-effect QTLs related to days to heading, panicle exertion and spikelet fertility were identified. The QTL qDH-3 on chromosome 3 showed the peak LOD score of 6.3, explaining up to 16.5% of phenotypic variation with additive effect of -2.6. Moreover, the QTL qPE-3 and qSF-3 on chromosome 3 were coincided with the QTL qDH-3 showing an opposite allele effects. Thus, the region harboring marker RM523-RM14281 could be helpful for the selection of cold tolerance genotypes in marker assisted selection(MAS) of rice breeding program.

Cold tolerance at every growing stage of rice(Oryza sativa L.) is one of the main determinations for the stable growth in temperature and high elevate area. In the current study, a 181 lines of BC population derived from a cross of Gayabyeo, a Tongil type sensitive to cold and Chhamrong a tolerant to cold were evaluated for cold tolerance with cold water irrigation(17℃) at seeding stage as well as low temperature germinate at 13℃, respectively. The resulting linkage map consists of 157 marker loci, covering all of 12 rice chromosomes and spanning 910cM(Haldane function) with an average interval of 76cM between markers. Three main-effect QTLs were identified. The comparison of the OTLs identified in this cold treatments resulted in an intriquing finding that each treatments were controlled by a major QTL. The QTL qCWI-4 on chromosome 4 was found to increase its additive effect to -0.84 as the cold water irrigate stress was given. In the meanwhile, the QTL qLTG-8 was detected with a LOD score of5.54, explaining up to 13% of the phenotypic variation controlled by Gayabyeo allele. In addition, the QTL qLTGV-3, controlled by Gayabyeo allele with a LOD score of 5.19 explaining about 12.5% of the variation was also identified. These results would favor our better understanding of the genetic control of cold tolerance in rice and be important for the development of rice cultivars with a broaden climatic adaptation.