Effect Of Genetic Background On Expression Of QTL For Drought And Salt Tolerance And Their Genetic Overlap In Rice

Salinity and drought are both two major abiotic stresses in rice (Oryza sativa L.) production worldwide. Improving salt tolerance (ST) and drought tolerance (DT) of rice is an important target for rice breeding programs. It's an efficient way to improve ST and DT by mining and pyramiding favorable QTLs from germplasms.In the present study, two indica varieties, IR64 (from IRRI) and Teqing (from Guangdong, China) were used as the recurrent parents, a japonica landrace, Binam (from Iran) was used as the donor parent to foster two sets of BC2F8 introgression lines. The two sets of advanced backcross introgression populations were used to identify QTLs affecting ST at the seedling and tillering stages and DT at the reproductive stage. The expressions of QTL under different genetic backgrounds and different environments, and genetic overlap of ST QTLs detected in different stages and genetic overlap of ST- and DT-QTLs were compared. Beneficial information was provided for breeding new rice varieties with ST and DT. The main results were summarized as follows.1. A total of 41 QTLs affecting survival days of seedlings (SDS), score of salt toxicity of leaves (SST), shoot K+ concentration (SKC), shoot Na+ concentration (SNC) , root K+ concentration (RKC) and root Na+ concentration (RNC) were identified under salt stress with the concentration of 140mM NaCl at the seedling stage in the two populations.2. Twenty-two QTLs affecting fresh weight of shoots (FW), tiller number per plant (TN) and plant height (PH) at the tillering stage were identified in IR64/Binam BC2F8 introgression lines. And sixteen QTLs were considered as ST-QTLs based on expression of QTLs under salt stress and non-stress conditions.3. In the two introgression populations a total of 47 QTLs affecting grain yield (GY), 1000-grain weight (GW), panicle number per plant (PN), filled grains number per panicle (GN ), spikelet number per panicle (SN), seed setting rate (SS) and plant height (PH) were detected under drought stress and non-stress conditions. And 37 QTLs were considered as DT QTLs which had contribution to DT.4. Comparing the distribution of ST-QTLs detected at the seedling and tillering stages, most (75.4%) of them were genetically independent. Only six were located in the same or adjacent chromosomal regions, suggesting partial genetic overlap of ST across the two stages occurs. It is likely, therefore, to develop ST rice variety for both stages by pyramiding of ST-QTLs of different stages or selection against the overlapping QTLs between the two stages via marker-assisted selection (MAS).5. Five chromosomal regions were identified to harbor both ST- and DT-QTLs in IR64/Binam population, while three in TQ/Binam population, indicating that there were genetic overlaps of ST and DT to some extent (23.4%). Rice variety with both ST and DT could be developed by selecting against the overlapping QTLs for ST and DT.6. By comparison of QTLs detected in different populations derived from same donor in different recurrent parent (IR64 and Teqing) backgrounds, and QTLs in the same genetic background under different environments (salt and drought stresses versus control), significant effects of genetic background and environment on expressions of ST- and DT-QTLs were observed. Even so, some main-effect QTLs insensitive to environment and genetic background were identified, e.g. QSnc3, QPn9 and QGw3. These QTLs show stability in different genetic backgrounds and environments, and may be beneficial for MAS breeding in rice for salt and drought tolerance.