Favorable Allele Mining Of Cold Tolerance At Seedling Stage By Reciprocal Introgression And Recombinant Inbred Line Populations In Rice

Unlike other grains,rice,as a temperature sensitive crop,is extremely susceptible to low temperature and chilling damage during its growth,resulting in a decline in yield and rice quality.Cold damage often hinders rice growth,affects its morphogenesis and leads finally to serious yield loss.Accordingly,identifying favorable genes tolerant to cold,and breeding elite rice varieties with cold tolerance is an effective way to solve this problem.In this study,two sets of reciprocal introgression lines and a set of recombinant inbred line derived from xian variety Minghui 63 and geng variety 02428 were evaluated for cold tolerance in climate chamber using cold tolerance-related traits such as wilting degree and survival rate after recovered growth.Based on the cold tolerance phenotypic data of rice seedlings,extreme materials were selected for physiological index testing to understand the physiological mechanism of cold tolerance in rice.Combined with the available Bin genotype data generated by previous re-sequencing,QTL mapping for cold tolerance at seedling stage was performed.Combined some 3K germplasms resources to explore favorable haplotypes,the results will provide novel germplasms and favorable genes for molecular improvement of cold tolerance of rice.The main results are as follows:(1)The malondialdehyde(MDA)content,peroxidase(POD)activity,superoxide dismutase(SOD)activity,and catalase(CAT)activity of extremely cold resistant materials and extremely cold sensitive materials were measured.The results showed that the antioxidant system in plants would be destroyed after prolonged low temperature stress,and the ability to remove reactive oxygen species in plants would be reduced,and the resistance of plants would be decreased accordingly.(2)13 QTLs for cold tolerance at seedling stage were identified on chromosomes 1,4,5,7 and 12,which explained 0.36% to 13.63% of phenotypic variation.No QTL was stably detected in different genetic backgrounds,whereas five QTLs were simultaneously detected for both wilting degree and survival rate on chromosomes 1,5,7 and 12.Among them,QTLs in the regions of 12 732 139～13 202 097 bp and 14 445778～14 585 009 bp on chromosome 1,and 14 658 891～15 684 510 bp on chromosome5 had high LOD values above 25 and were considered as reliable main-effect QTLs.98 pairs of epistatic QTLs were located in MH63-ILs and RIL,and the two populations jointly located epistatic QTLs located in the 3 427 719～2 365 667 bp and 1 787 320 ～ 3056 226 bp intervals on chromosome 6.(3)Combined with gene annotation,gene expression profile and phenotyping data of cold tolerance of 3K germplasms,the previously cloned gene Os WKRY45 for cold tolerance was regarded as the responsible gene for the QTL in the region of 14 658891～15 684 510 bp on chromosome 5,while the two candidate genes,LOC＿Os01g25540 and LOC＿Os01g25560 in the two regions on chromosome 1,were the new candidate genes for both wilting degree and survival rate.Haplotype analysis indicated that Hap9 of LOC＿Os01g25540 and Hap8 of LOC＿Os01g25560 are favorable haplotypes for cold tolerance.