| With six physiological traits (i.e., sodium content, superoxide dismutase activity, malondialdedyde content, relative electric conductivity, proline content and water content) and the dose of 50% inhibition of seedling height as indexes, mapping of QTLs underlying the salt tolerance of rice was conducted with the method of composite interval mapping, based on a recombinant inbred (RI) population consisting of 131 lines (Fjo) derived from a cross between two indica rice varieties, Acc8558 and H359, via single seed descent and on a corresponding genetic map comprising 147 RFLP markers and 78 AFLP markers. Meanwhile, QTLs controlling chrolophyll content were also analyzed. The main results were summaried as follows:(1) Under the salt stress of ISOrnmol NaCl, All examined traits of rice seedlings of the RI population displayed continued variation and an approximately normal distribution, indicating that all of these traits were quantitatively inherited.(2) Analyses of correlation between traits showed that the correlation coefficients between Na+ content and relative electric conductivity, proline content and water content were all positive and significant at the level of 1%; the correlation coefficient between Na~ content and SOD activity was negative and significant at the level of 5%; malondialdedyde content and SOD activity were positively correlated at the level of 5%, The correlation coefficients between the doses of 50% inhibition of plant height at the three observation times (12d, 18d and 24d) were all significant at the level of 1%. But no linear correlation was found between physiological characters and the dose of 50% inhibition of plant height.(3) 21 QTLs for Na+ content were detected on chromosomes 1, 3, 5, 6, 8, 9, 10, 11 and 12, which could explain 79.63% of phenotypic variance. Among the QTLs. qSClc had the largest additive effect and could explain 15.23% ofthe total phenotypic variance. This QTL was located at the same interval with the half dwarf gene sdl, suggesting that the sdl gene could probably improve the salt tolerance of rice by reducing the Na+ content.(4) Eight QTLs for SOD activity were detected on chromosomes 1, 2, 3, 4, 7, 8 and 9, which could explain 42.44% of phenotypic variance.(5) Three QTLs affecting MDA content were detected on chromosomes 1 and 3, which could explain 13.56% of phenotypic variance.(6) Seven QTLs concerning relative electric conductivity (REC) were detected on chromosomes 1, 2. 3. 6. 9 and 11, which could explain 39.78% of phenotypic variance.(7) Ten QTLs for proline content were detected on chromosomes 1, 2, 3, 4, 7, 8, 9 and 11, which could explain 41.16% of phenotypic variance.(8) Seven QTLs affecting water content were detected on chromosomes 1, 3, 5, 8 and 9, which could explain 30.23% of phenotypic variance.(9) The number of QTLs detected for the doses of 50% inhibition of plant height (PHDso) of seedlings increased with time quickly, with 3, 8 and 14 QTLs detected at 12d. 18d and 24d respectively, and basically new QTLs appeared on the basis of former QTLs. In addition, the phenotypic variance explained by these QTLs also increased with time. These results implied that genes relevant to salt adaptability were turned on step by step along with the time of salt stress. This phenomenon was consistent with the gradual increase of PHDso with time.(10) QTLs concerning salt tolerance were found on all chromosomes, and a few QTLs for different indexes were mapped at the same locations. But the number of QTLs detected on chromosome 1, 3 and 9 were the most, suggesting that the three chromosomes were more important for salt tolerance.(11) Six QTLs for contents of chlorophyll a and chlorophyll b were detected respectively, among which five QTLs were the same between the twocharacters. These QTLs were mainly distributed on chromosomes 1 and 4, indicating that the two chromosomes were more important for chlorophyll content. qChlAlc and qChlBlb (these two QTLs were mapped at the same...
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