| Rice is moderate susceptible to salt. Lower concentration (0.3%) of sodium chloride can inhibit its growth, eventually leading to a decline in production. With the increase or aggravation of industrial wastewater, sewage emissions, heavy use of pesticides and fertilizers, unreasonable irrigation, as well as the area of cultivated salinization, salt stress has become an important factor in agricultural production. Full study of the genetic mechanism of salt-tolerant rice, and developing new varieties of salt is the most effective way to reduce salinity. In this study, QTLs for salt tolerance (ST) related traits including score of salt toxicity of leaves (SST), survival days of seedlings (SDS), shoot K+ concentration (SKC) and shoot Na+ concentration (SNC) were detected using a set of reciprocal introgression lines (ILs) derived from a japonica variety 'Lemont' and an indica variety 'Teqing' under salt stress treatment with the concentration of 140 mmol·L-1 NaCL in a greenhouse and phytotron, with a view to reveal the effect of genetic background on salt-tolerant QTL, providing a scientific basis for rice genetic improvement of salt-tolerant traits.The main experimental results were described as follows.1. Based on genotype data of the reciprocal introgression lines by the same 151 SSR markers and three morphological markers, Lemont genome on the average accounted for 83.8% in Lemont background-ILs whereas 88.9% of Teqing genome in Teqing background-ILs. Most genetic background of the two sets of ILs was similar to their respective parent. The two reciprocal ILs averagely shared around 11.1-16.2% of common genome.2. Continuous variation and transgressive segregation for all ST-related traits were observed in the two IL populations with overlaps of frequency distributions for most traits. In Lemont background, the number of introgression lines with SST smaller than 3 score and SDS longer than 14 days were 4 and 2 while in Teqing background, the number of lines for the two triats were 6 and 6, respectively, suggesting the gene effect of the two parents in the reciprocal backgrounds on each ST-related trait was almost equivalent.3. SST and SDS showed a significant negative correlation in the reciprocal IL populations by the correlation analysis, indicating that the more serious salt toxicity of leaves, the shorter survival days of seedings. SNC in greenhouse and phytotron were significantly or very significantly positively correlated with SST, and negative correlation with SDS in Lemont background-ILs, showing that the higher Na+ content in leaves, the shorter of survival days. SKC and SNC were highly significant negative correlation in greenhouse and phytotron of Teqing background-ILs. SKC and SNC were highly positively correlated between greenhouse and phytotron of two-way ILs, indicating that the trends of K+ and Na+ are consistent at the two environments.4. Eighteen QTLs for all ST-related traits were identified in each of the two IL populations. No any a common QTL for the same trait was detected in the reciprocal IL populations, indicating there was a strong genetic background effect on expression of ST-QTL, and also suggesting these ST-QTLs had relative small phenotypic effect.5. Only one common QTL affecting SKC was identified in Teqing background-ILs under green house and phototron environments, indicating there was a strong interaction of ST-QTL by environment.6. The two parents, Lemont and Teqing are moderate susceptible to salt stress, QTL mapping results indicated that some favorable alleles beneficial to improvement of ST-related traits do exist in the parents. Therefore, it is possible to develop a new variety with improved ST level by identifying and mining this kind of 'hidden' ST-genes existed in the modern varieties through molecular marker technology and further pyramiding these non-allelic alleles via marker-assisted selection.
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