Study On Effects Of Genetic Background And Environment On Expression Of Salt Tolerant QTL In Rice

Rice is the staple food for most Asian people. Salinity is considered one of the most major abiotic stresses limiting rice productivity throughout the world. Improving salt tolerance of rice is one of the most important objectives of rice breeding programs, which can be better to mapping QTLs related to salt tolerance for MAS-based rice breeding. In this study, two advanced backcross populations were evaluated for morphological and physiological traits related to salt tolerance at the seedling stage under the green house and phytotron conditions. QTLs affecting salt tolerance and their expressions in different genetic backgrounds and environments were examined and compared.Two moderate salt-susceptible indica varieties, IR64 (from IRRI) and Teqing (from China) were used as the recurrent parents, a japonica landrace, Tarom molaii (from Iran) was used as the donor parent. Two BC₂F₈ populations were developed by random consecutive backcrossing, and were evaluated under salt stress with the concentration of 140mM NaCl at the seedling stage under the green house and phytotron conditions. Correlation analysis indicated that survival days of seedlings (SDS) was highly negatively correlated with shoot Na⁺ concentration (SNC), positively with shoot K⁺ concentration (SKC), and had no correlation with root K⁺ concentration (RKC) and root Na⁺ concentration (RNC), indicating salt toxicity of leaves or salt tolerance resulted from over-accumulation of Na⁺ in the shoots and had nothing to do with ions situation in the roots. RKC was highly positively correlated with RNC and both of them had no correlations with SKC and SNC, respectively, suggesting different mechanisms existed between uptake of K⁺ and Na⁺ in the roots and their transportation from the roots to the shoots. Fifty-seven QTLs affecting the seven salt-tolerance related traits including score of salt toxicity at 10 and 16 days after salinisation (S10D, S16D), SDS, SKC, SNC, RKC and RNC were identified in two BC₂F₈ backcrossing introgression populations under the two environments, which distributed on the 11 chromosomes except chromosome 10. The QTLs affecting SKC and SNC were not observed to distribute in the same genomic regions with the QTLs of RKC and RNC, respectively, which further showed different genetic mechanisms involved in uptake of K⁺ and Na⁺ between the roots and the shoots. Compared to the previous mapping results in different mapping populations by same markers, 1/4 of 57 QTLs for the seven related traits were located to the same or near genome regions. The regions of RM583-RM23 on chromosome 1, RM240-RM112 on chromosome 2, and RM60-RM231 on chromosome 3 were identified for QTLs affecting S10D, S16D, SDS, SKC and/or SNC in the green house and /or phytotron, which are considered as important genomic regions related to salt-tolerance for MAS-based breeding.By comparison of QTLs detected in different populations derived from same donor in different recurrent parent (IR64 and Teqing) backgrounds, and in the same genetic background under different environments (green house and phytotron), significant effects of genetic background and environment on expressions of the ST QTLs were revealed. The same QTLs detected in two different genetic backgrounds or environments may have different effect values or/and directions of gene effect. Some main-effect QTLs insensitive to environment, e.g. QPsnc2 and QGsnc3 for SNC were identified. These important QTLs and genomic regions mentioned above will be greatly beneficial to the MAS-based breeding for salt tolerance in rice.