Improvement And QTL Mapping For Low Nitrogen Tolerance Using Selected Introgression-line In Rice

Nitrogen is one of the essential nutrients that are vital to plant growth. Also, it is oneof the most important mineral elements. In the process of rice cultivation, the appliedamount of nitrogen per unit area and a low utilization rate has become the two biggestproblems constraining its development. The relevant mechanisms of uptake, transport andutilization efficiency of nitrogen are still a mystery. The research on the mechanism ofnitrogen metabolism and how to improve the utilization efficiency of nitrogen absorptionprovided an economic, environmental, and long term strategy for ensuring the sustainablerice production in China. In this study, Shuhui527(SH527) and Minghui86(MH86), whichwere two widely used elite indica restorers in China, were used as recurrent parents,2004and TKM9as donors for developing four BC2F4selected backcrossing populations(SH527/2004, MH86/2004, SH527/TKM9and MH86/TKM9. Eight important agronomictraits, including plant height, panicle length, panicle number per plant, filled-grain numberper panicle, total grain number per panicle, spikelet fertility, thousand grain weight andgrain yield were conducted for phenotypic evaluation and QTL mapping under normalcontrol and low nitrogen stress conditions. The main results were summarized as follows:1. Among the eight agronomic traits, thousand grain weight, spikelet fertility andpanicle number per plant were greatly affected by low nitrogen stress, leading to thereduction of yield. The lines with high ability of tillering, high spikelet fertility and stablethousand grain weight should be considered in the practical breeding.2. The correlation analysis results showed that grain yield per plant was significantlyor extremely significantly positive correlated with flled-grain number per panicle, totalgrain number per panicle and spikelet fertility. Thousand grain weight and flled-grainnumber per panicle, total grain number per panicle and grain yield per plant were insignificantly or extremely significantly negative correlations. It is indicated that we shouldnot only consider the ability of tillering, flled-grain number per panicle and spikeletfertility, but also pay attention to the coordination of flled-grain number per panicle andspikelet fertility in the high yield breeding.3. The results of path analysis showed that panicle number per plant provided the largest direct effect for grain yield, and filled-grain number per panicle had a large indirecteffect on this. Thus, it is important to improve the panicle number per plant and filled-grainnumber per panicle simultaneously which is consistent with the correlation results.4. The results of identification of QTLs showed that18QTLs were stably expressedunder low nitrogen stress and normal conditions with the explained phenotypic variationpercentage ranging from10.57%to32.96%. The favorable alleles are from donor parents.Thus, these loci could be used as important loci in the improvement of yield traits. Forexample, qfgp6, qfgp12, qsnp6a and qsnp12in the Shuhui527/2004population; qph2,qpl12a and qsf3in the Shuhui527/TKM9population.34QTLs were detected using the difference of trait values between normal and stressconditions with the explained phenotypic variation percentage ranging from7.32%to20.2%. The favorable alleles are from donor parents. For example, qph2a and qph5controlling plant height were identified in the Shuhui527/2004population. qfgp12controlling filled-grain number per panicle in the Shuhui527/TKM9population, qtgw3aand qtgw5controlling thousand grain weight in the Minghui86/2004population. qsnp12controlling total grain number per panicle in the Minghui86/TKM9population. These locireduced the difference of trait values of target traits, indicating that they had directcontributions to the low nitrogen tolerant.14pleiotropic QTLs were identified under low nitrogen stress and normal conditionswith the explained phenotypic variation percentage ranging from13.52%to25.68%. Thefavorable alleles are from donor parents. For example, qfgp11、qsnp11and qyd11(nearRM286) controlling filled-grain number per panicle, total grain number per panicle andgrain yield per plant, respectively. These three traits could be simultaneously improved bythe introgressed alleles of TKM9. Some pleiotropic QTL were unfavorable for thesimultaneously improvement of different traits. For example, qsnp7b and qtgw7(nearRM346), the favorable alleles from donor Minghui86can improve filled-grain number perpanicle while the favorable alleles from2004can improve thousand grain weight. Thoseloci should be applied alternatively according to different breeding goals.