Dissection And QTL Mapping Of Low-phosphorus Using Selected Introgression Lines In Rice (Oryza Sativa.L.)

In this study, Shuhui527 and Minghui86, the two widely used elite indica restorers in China, were used as recurrent parents, two indica varieties Yetuozai and 2004 as donor for developing four backcrossing introgression line (IL) populations. The bulks of four BC2F2 backcrossing populations were imposed critical screening for low phosphorus tolerance (LPT) under the red soil condition with phosphorus deficiency in Xuancheng, Anhui province. The progeny of the BC2F4 populations and their parents were tested for comprehensive phenotypic evaluation in the whole growth stage at the field condition.Meanwhile, the two IL populations were investigated at seedling stage using nutrient solution in the glasshouse.1. Compared with the control condition, B treatment (normally fertilizing under barren soil) caused the significant reduction of plant height and spikelet number per panicle of the recurrent parent Shuhui527 and Minghui86, but no significant changes were observed in panicle number per plant, spikelet fertility and thousand grain weight, resulting in the yield loss of Shuhui527 and Minghui 86 under B treatment. Under P treatment (phosphorus stress under barren soil), plant height, filled-grain number per panicle, thousand grain weight, grain yield per plant and harvest index of Shuhui527 and Minghui86 were significant affected, while panicle number per plant and spikelet fertility were not obviously affected, indicating the reduction of filled-grain number per panicle and thousand grain weight were the main reason for the changing of grain yield of Shuhui527 and Minghui86. Transgressive variations were observed among the measured traits in four populations, indicating the presence of a wide range of separation of each trait.2. Compared with the control condition in Beijing, root-shoot ratio of IL was significantly increased in Shuhui527/Yetuozai population under F treatment (phosphorus deficiency treatment); root length, total dry weight and root-shoot ratio were significantly increased while biomass was significantly decreased in Minghui86/Yetuozai population. From the results above, we found that root-shoot ratio was sensitive to low phosphorus stress, the reason was that plants need to absorb more phosphorus and develop stronger root system in order to adapt the low phosphorus stress. Under F treatment, root length, root length/shoot height displayed highly sensitivity; therefore, these traits can be used as indicators in the screening of superior lines using water culture method.3. Grain yield per plant was significantly positive correlated with panicle number per plant, filled-grain number per panicle, spikelet number per panicle and grain yield per plant in four populations under three treatments. Therefore, we should consider these traits as a priority in practical breeding, and coordinate with other yield components.4. A total of 68 (55.3%) main-effect QTLs which had favorable alleles from donor parent Yetuozai or 2004 underlying 11 yield and its related traits were identified of four populations in LangFang. A total of 85 main-effect QTLs were identified for 9 measured traits of two populations in Beijing, the contribution of phenotypic variations ranged from 7.5% to 27.6%. Of which,10.6% QTLs can be detected repeatedly under two or more treatments, especially those QTLs associated with root length, root length/shoot and root-shoot ratio which displayed consistent phenotypic effects.5. Based on the performances of grain yield per plant under low phosphorus stress in Langfang,1,13,6 and 7 lines which had significant higher yield than the recurrent parent were identified in Shuhui527/Yetuozai, Minghui86/Yetuozai, Shuhui527/2004 and Minghui86/2004 population. The dissection the genotype of superior lines of combining with identified QTLs under low phosphorus and showed that RM481 and RM402 were important QTLs for further improvement of DLT of Shuhui527. RM335, RM5463, RM219, RM254, RM341, RM571, RM316 and RM224 were important regions of Shuhui527 for maintaining stable yield under low phosphorus stress condition. RM200, RM6959, RM108 were important QTLs for further improvement of DLT of Minghui86. RM335, RM169, RM254 and RM5349 were important regions of Minghui86 for maintaining stable yield under low phosphorus stress condition. These QTLs would be key candidate regions for low phosphorus molecular breeding. Some superior ILs were identified under the overlap screenings in the field at the whole growth stage and in the greenhouse at seedling stage using water culture method. These lines could not only be used as materials for the breeding of high efficient use of phosphorus varieties, but also used for the dissection of genetic mechanisms of DLT.