QTL Mapping For Controlling Seedling Cold Tolerance In Dongxiang Wild Rice (Oryza Rufipogon Griff.)

Cold stress is one of the major environmental stresses affecting rice (Oryza sativa L.) production, and that low-temperature stress is one of restricting factors in the development of rice at seedling stage in early-spring and high-elevation environments. So that it has an important significance for high and stable yield of rice to find genetic resource and breed new variety with cold tolerance, especially find and utilize cold-tolerant gene from Dongxiang wild rice (O. rufipogon Griff., hereafter referred to as Dwr), which is the northernmost wild rice.We used the strong cold-tolerant variety Dwr as the donor parent, and the cold-sensitive cultivar Xieqingzao B (O. sativa sp. indica Kato, hereafter referred to as Xqz B) as the recurrent parent to construct two primary mapping populations BC₁F₁₀ and F2, which were used to assess the seedling cold tolerance of Dwr by genetic analysis and QTL mapping. The control lines included the strong cold-tolerant variety Longdao 5 (O. sativa sp. japonica Kato, hereafter referred to as Ld 5), and the parents. The results were summarized as follows:â'ˆSeedling cold tolerance genetic analysis of DwrGentic analysis for the seedling cold tolerance of a BC₁F₁₀ population consisting of 228 lines, derived from a backcross between Dwr and Xqz B, by cold treatment assay (10°C for 7 days), and seedling wilting rate and seedling mortality rate were used as evaluation indices. The result showed that the mean seedling wilting rate and seedling mortality rate for the population of BC₁F₁₀ was 67.40% and 70.80%, respectively. Moreover, the skew-normal and continuous distribution of seedling wilting rate and seedling mortality rate, and the 1:3 proportion of cold tolerance separation between cold tolerance and cold intolerance, suggested that cold tolerance at seedling stage in Dwr was inheritance of qualitative-quantitative traits, major quantitative trait locus (QTL) be existed.Genetic analysis for the seedling cold tolerance of a F_2:3 population consisting of 265 lines, derived from a cross between line 5339 and Xqz B, of which line 5339 was a strong cold-tolerant line screened from BC₁F₁₀ by cold treatment assay (10°C for 7 days), and seedling mortality rate was used as evaluation index. The result showed that there were significant differences in seedling mortality rate of each line of the F_2:3 population, varied from 6.13% to 100%, and the mean seedling mortality rate was 69.76%. Moreover, the continuous distribution of seedling mortality rate, and the 1:3 proportion of cold tolerance separation between cold tolerance and cold intolerance, further suggested that cold tolerance at seedling stage in Dwr was inheritance of qualitative-quantitative traits controlled by major-minor genes.â'‰QTL mapping of seedling cold tolerance in DwrThe genetic linkage map of a BC₁F₁₀ population consisting of 239 lines, derived from a backcross between Dwr and Xqz B, was constructed with 130 pairs of SSR markers. The QTL for seedling cold tolerance (SCT) was identified by composite intervals mapping. There were two QTLs for seedling cold tolerance (qSCT-1 and qSCT-12) detected. The location of qSCT-1 was in the interval RM246-RM1095 on chromosome 1, and the location of qSCT-12 was in the interval RM519-RM270 on chromosome 12, explaining 53.34% and 12.07% of phenotypic variance, respectively.The genetic linkage map of a F2 population consisting of 276 lines, derived from a cross between line 5339 and Xqz B, of which line 5339 was a strong cold-tolerant line screened from BC₁F₁₀ by cold treatment assay, constructed with 64 pairs of markers. Seedling mortality rate of the F_2:3 population represented the genotype of the F2 population. The QTL for seedling cold tolerance (SCT) was identified by composite intervals mapping. One QTL for seedling cold tolerance (qSCT-4) was detected. The location of qSCT-4 was in the InDel marker S47M on chromosome 4, explaining 1.55% of phenotypic variance.Total three QTLs for controlling seedling cold tolerance of Dwr were detected in the two mapping populations, which can lay a foundation of fine mapping and cloning cold-tolerant gene in Dwr, and can help marker-assisted selection for enhancing the efficiency and accuracy in screening cold-tolerant rice.