QTL Mapping For Abiotic Stress Tolerance And Probing Their Genetic Overlap In Lowland Rice And Upland Rice

There were two ways to improve crop yield:increasing per unit area yield and enhancing corps abiotic stress tolerance. According to statistics, the yearly grain yield loss was up to about 1,000 billion kilograms in recent 5 years due to adverse environmental conditions, which was the most import factor in crop production. Crop abiotic stress tolerance, as the complex quantitive traits, was hard to be enhanced by traditional breeding methods, but it can be done by unraveling abiotic stress tolerance genetic mechanisms with the continuous improvement of quantitative trait locus (QTL) theory and method and the construction of high-density genetic map.In this study, IAPAR-9 (upland rice) was crossed with two lowland rice, Liaoyan241 and Akihikari, and fostered two recombinant inbred lines (RILs). The two RILs were used to study genetic background and environmental effects on expression of QTLs for abiotic stress tolerance (cold, drought, salidiy, and Nitrogen Efficiency), and genetic overlap of these QTLs were compared. All of results aimed to better understand abiotic stress tolerance mechanisms and provide more beneficial QTLs, and to provide theoretical basis for fine mapping and molecular marker-assisted breeding of abiotic stress tolerance by identifying stable QTLs across environment and genetic backgrounds. The application of genetic overlap to breeding for abiotic stress tolerance was also discussed. These main results were summarized as follows:1. A total of 64 QTLs referring some traits correlated with nitrogen utilization efficiency were detected in the two RILs, forming 16 clusters in rice chromosomes. The 16 QTL clusters in chromosomes would be used in MAS rice breeding. The interval, RM3421-RM5404, in chromosome 2 and the adjacent interval with RM8264 in chromosome 8, where QTLs underlying traits associated with nitrogen utilization efficiency stably expressed across different genetic backgrounds and environment, may be beneficial MAS for nitrogen efficiency in rice.2. A total of 314 QTLs underlying 11 and 7 main agronomy traits in Jilin and Hainan province, respectively, were detected under drought stress and non-stress conditions in two RILs, among them 108 QTLs had contribution to drought tolerance. There were 13 and 12 chromosome intervals, respectively, where QTL stably expressed across two drought stress conditions and two RILs. The total 25 chromosome intervals may be beneficial MAS for drought tolerance in rice.3. A total of 69 QTLs affecting 8 main agronomy traits were identified in two RILs under salinity stress and non-stress in Tanghai county. The 17 QTLs which had contribution to salinity tolerance were distributed 16 intervals on chromosomes, and only 2 intervals among them, where QTLs stably expressed across different two RILs, may be beneficial MAS for salinity tolerance in rice.4. A total of 88 QTLs affecting 5 main agronomy traits were identified in two RILs under cold stress and non-stress in Jilin province. The 25 QTLs which had contribution to cold tolerance were distributed 21 intervals on chromosomes, and the 2 intervals among them, where QTLs stably expressed across different two RILs, may be beneficial MAS for cold tolerance in rice. In addition, 61 QTLs affecting main agronomy traits were identified in two RILs under nature low temperature in Kunming city, and which further indicated genetic background had a significant impact on QTL expression of main agronomy traits under cold stress.5. A total of 3 QTLs affecting survival days of seedlings (SDS) at seedling stage were identified in two RILs under alkaline stress,which had genetic overlap with salinity tolerance QTLs identified by previous studies, and the alleles contributed to alkaline tolerance were all from the parents except IAPAR-9.The 3 QTLs may be beneficial MAS for salinity-alkaline tolerance in rice.6. There were genetic overlap among abiotic stress tolerance to some extend,and the intervals harboring multiple stress tolerance QTLs distribute on all 12 chromosomes,maybe hot spot regions existed, such as the adjacent interval with RM3482 in chromosome 1, which was identified to harbor multiple abiotic stress tolerance QTLs in two RILs in this study. The results offered useful information for molecular breeding of multiple abiotic stress tolerance.