Construction Of Genetic Linkage Map Based On SSR Marker And Mapping Of QTLs Related To Cold Tolerance Using A RIL Population In Rice (Oryza Sativa L.)

Rice is one of the most critical cereals in China. It has been expected that breeding of varieties with high yield, good quality and multiple resistance by breeders and farmers. Because of the quantitatively-genetic nature of the traits related to yield, quality and resistancees to various stresses, it is fundamental to explore special resourcees with elite agronomic traits, mapping corresponding position by molecular markers, cloning of corresponding genes and breeding of rice by MAS (Molecular marker-assisted selection) .In this study 227 lines (F7) were randomly selected among a RILs (Recombination Inbreeding Lines) population extracted from a cross between IR₂₈, a cold-susceptible indica variety, and Da-guan-Dao, a cold-tolerance japanica, and used to construct a molecular linkage map. With this map the cold tolerance of rice seedling and seed germination ability under low temperature were genetically analyzed. The main results were described as follows:1. Total 1095 SSR (Simple Sequence Repeat) markers were used to screen the polymorphism between two parents (IR₂₈ and Da-Guan-Dao). Among 269 SSR markers with polymorphism, 167 were finally used to construct a genetic linkage map in a population of 227 lines. It spans 1837.2 cM in length covering all 12 chromosomes, with an average density of 11.0cM. Several distorted segregation regions was detected according to Chi-value of all 167 marker loci. Then the genetic map was tentatively adjusted with a multiple-point method. Based on the adjusted map 29 SDLs (Segregation-distorted loci) were located on 12 chromosomes.2. The seedlings of 227 lines with 2-3 leaves were subjected to 9℃for 5 days and subsequently slow recovery of 5 days in growth chambers. The scoring was done to characterize the cold tolerance of two parents and RILs (Fs) according to the percentage of dead seedling after recovery. The result show that DaGuanDao was tolerant with a score of 2 while IR₂₈ susceptible, with a score of 9. The RIL population exhibited all range of scores from 1-9, presenting continuous distribution. It was detected that three QTLs accounting for 38.1% of total phenotypic variation located on 8 and 11 chromosomes respectively. The qSCT-11-1, a major QTL, located between RM26281 and RM3701 on 11 chromosome accounted for 23.0% of total phenotypic variation. The qSCT-11-2 located between RM7248 and RM5731 closely flanking qSCT-11-1 explained 10.1% of total phenotypic variation. The qSCT-11-2 located on 11 chromosome flanked by RM22491 and RM22694 explained 8.1% of total phenotypic variation. All three QTL alleles from japonica parent decreased the percentage of seedling death.3. In order to map QTLs conferring low temperature germinability (LTG) it was observed germination rate percentage at 14°C for 8,10,12 days of two parents and 227 RILs (Fg) after soaking. Germination rate percentage at 14°C for 8% 10% 12 days of two parents were obviously different and that of the RILs distributed continuously. Two Putative QTLs on chromosome 1 and 11, associated with low-temperature germination were detected. The total phynotypic variation explained by qLTG-1, a newly-detected QTL at 10 day and 12 day on chromosome 1 were 18.4% and 16.8% respectively. The additional QTL, qLTG-11, detected at 8 day on chromosome 11 accounted for 24.5% of the total phenotypic variation for low-temperature germinability. Both alleles in qLTG-1 From IR 28 and that at the region of qLTG-11 from DaGuanDao increased the low-temperature germination rate.