Mapping Of Quantitative Trait Loci Associated With Heat Tolerance At Flowering Stage In The Rice (Oryza Sativa L.) Variety, 996

Rice is highly sensitive to high temperature stress (HTS) at flowering stage that is likely to become one of major abiotic stresses in rice growing areas in future climates. Identifying genes/QTLs and breeding rice varieties with tolerance to HTS at flowering stage are therefore essential for adaptation to climate warming. In this study, a recombinant inbred lines (RILs) population consisted of 286 RILs, which derived from a cross between the HTS tolerant rice cultivar 996 and the sensitive cultivar 4628, was developed with single seed descent (SSD) method. The QTL analysis was conducted, with seed set percentage (SSP) and pollen fertility (PF) as the heat tolerance indicators for the lines grown in both field and greenhouse under HTS at flowering stage, and with the genome-wide genetic linkage map constructed with SSR and SFP markers. The main results were as follows:1. The seed set percentage for the RILs (F9) and the two parents were measured both in the field and greenhouse stressed with high temperature at the flowering stage. The two parents,996 and 4628, showed highly significant differences in the response to HTS both in the field and greenhouse conditions. A large variation to HTS in the RILs was also observed for seed setting rate in the field and growth chamber, and their seed set percentage showed a normal frequency distribution. The SSPs of the two treatments were positive correlated significantly, with a correlation coefficient of 0.69.2. The pollen fertility percentage for the RILs and the two parents were measured in the field high temperature growth environment at the flowering stage. The two parents,996 and 4628, showed highly significant differences of the pollen fertility percentage in the response to HTS. The pollen fertility of RILs exhibits a normal frequency distribution. The correlation coefficient between the seed set percentage and pollen fertility percentage is 0.57, with significantly at 1% level.3. A total of 928 SSR and SFP markers were screened for the polymorphism between the parents of 996 and 4628.162 polymorphic SSR and SFP markers were used for the construction of a genetic linkage map using the RIL population. The linkage map spanned 2025.2 cM in length, with an average distance of 12.5 cM between adjacent markers.4. Two QTLs associated with seed set percentage (SSP) stressed with high temperature were detected on chromosome 4 and 10 in two HTS environments. The QTL on chromosome 4, is located in the interval flanked by the markers RM5687 and RM471, with a LOD score of 13.63 and 15.43 in the field and growth chamber conditions, with contribution rate 21.32% in the field conditions and 25.82% in the greenhouse to the total phenotypic variation, respectively. The allele from 996 was associated with the increased seed setting rate of 9.11% in the field and 9.32% in the greenhouse under HTS. The QTL on chromosome 10, is also located in the same interval flanked by the markers RM6132 and RM6100, with a LOD score of 6.61 and 7.17 in the field and greenhouse conditions, with contribution rate 11.50% in the field conditions and 11.63% in the greenhouse to the total phenotypic variation, respectively. The allele from 996 was associated with the increased seed set percentage of 7.24% in the field and 6.99% in the greenhouse under HTS.5. Two HTS QTLs were detected on chromosome 4 and 6, taking the pollen fertility rate as a heat tolerance index, under the natural field high temperature. The QTL on chromosome 4, was located in the interval flanked by the markers RM5687 and RM471, with a LOD score of 7.54 and contribution rate 15.1%. The QTL on chromosome 6, is located in the interval flanked by the markers RM190 and RM225, with a LOD score of 4.43 and contribution rate 9.31%.