QTL Mapping Of Phosphorus Deficiency Tolerance At Two Development Stages In Rice (Oryza Sativa L.)

The low level of available phosphorus in soils is a major yield-limiting factor in rice production. Breeding high phosphorus efficient cultivars may represent a more sustainable solution than sole reliance on fertilizer application. Molecular marker assisted selection (MAS) can be integrated with traditional methods of artificial selection on phenotypes to breed rice cultivars with high phosphorus efficiency. Wheares QTL mapping is the basis of the MAS and map-based cloning. The present research mainly aimed to map QTLs for traits related to phosphorus deficiency tolerance at tillering stage and heading stage in rice after increasing the density of rice genetic linkage map with a number of 35 SSR markers. In addition, the rice root acid phosphatase was evaluated and its relationship with phosphorus efficiency was studied. A RIL population consisting of 195 lines derived from maintainer line Xieqingzao B (abbreviated as Xie B) and restoring line Zhonghui 9308(abbreviated as R9308) of super hybrid rice Xieyou 9308 was used and hydrophonic method was employed in the experiment. The relative parameter, defined as a ratio of value under phosphorus deficient condition to that measured under sufficient condition was used to evaluate the tolerance ability of parents and RIL population in the experiment. The main results are outlined as follows:1. A total of 328 SSR markers were used to screen the polymorphism between Xie B and R9308, and 98 polymorphic markers were obtained with the polymorphism rate of 29.8%. Based on the preliminary framework of the linkage map, 35 polymorphic markers were chosen to genotype the RIL population consisting of 281 lines. The chi-squares test indicated that a number of 18 markers which accounted for 51.4% were consistent with theoretical segregation ratio of 1:1 at the significance level of 5%, and the other 17 markers which accounted for 48.6% deviated significantly. Among all the deviation markers, 7 markers deviated to male parent R9308 and the other 10 deviated to female parent Xie B. By using MAPMAKER/EXP 3.0, all the 35 SSR markers were localized onto the chromosomes. The marker-newly-added linkage map consists of 198 SSR markers and covers a length of 1765.6 cM with the average distance of 8.96 cM between adjacent markers.2. By using CIM method, a total of 21 additive QTLs for phosphorus deficiency tolerance related traits were detected at two development stages, which distributed through chromosome 4, 5, 6, 7, 10, 11. Among them, 4 was for relative root dry weight(RRDW), 3 was for relative shoot dry weight(RSDW), 3 was for relative total dry weight(RTDW), 5 was for relative root length(RRL), 4 was for relative tillering ability(RTA) and 2 was for relative root/shoot ratio(RRRS). In addition, 3 pairs of epistatic effect between QTLs which have no additive effect were also detected on chromosome 1, 5, 6, and 9. At tillering stage, QTLs for RSDW, RTDW and RRRS were detected at the same region of RM307-RM5953 on chromosome 4 and QTLs for RRDW and RTA were detected at the same region of RM311-RM6142 on chromosome 10. The situation that QTLs for different traits localized at the same region was also found at heading stage. Except for RRL, same QTLs were detected for the other 5 traits at the same region at tillering stage and heading stage. Interestingly, among three pairs of epistatic effect, one pair was detected at two development stages. A cluster of QTLs were detected at the region of RM307-RM5953 on chromosome 4 in which phosphorus efficiency related gene may lie.3. Under phosphorus surficient condition, the root acid phosphatase activity of male parent R9308 was higher than that of female parent Xie B. Under phosphorus stress condition, however, the situation is quite reverse although the root acid phosphatase activity of the parents and RIL population lines increased at both development stages, which indicated that the genetic system for acid phosphatase under stress condition was different with that for acid phosphatase under normal culture. The simple correlation analysis showed that the contribution of AAP to phosphorus efficiency at tillering stage was greater than that of at heading stage. There were two QTLs for RRAPA at tillering stage, but no QTL was detected at heading stage.