Studies On Drought Tolerance And High Nitrogen Use Efficiency Of Introgression Lines Derived From Multiple Parents In Rice

With the water crisis and the worsening of environmental pollution,improving drought tolerance(DT) and nitrogen utilization efficiency(NUE) of rice become an important target for rice breeding programs,it is the most effective methods to improve DT and nitrogen NUE of rice verities by discovering and applying DT and NUE QTLs from germplasm.The new strategy of molecular breeding to combine QTL discovery with crop breeding can be conducted by screening the target trait of introgressed lines(ILs) derived from large scale backcross and genotyping ILs.Furtherly,favorable QTLs can be Pyramided by intercross ILs with DT and NUE QTLs from different donors assisted by marker selection.In this study,Zhong413,a wide compatible restore line,was used as recurrent parent(RP),to cross and backcross with 10 elite varieties(donors) originated from countries or regions to foster BC2F2 introgression lines.The bulks of BC2F2 populations were imposed critical selections for DT and NUE under severe drought stress and low nutrition,the survived were selfed to form BC₂F₃ population. Pyramiding populations were developed by making crosses between BC₂F₃ ILs and imposed repeatedly DT and NUE selections in F₂,from which 112 pyramiding lines were repeatedly phenotyped under DT,low nitrogen level(LN),medium nitrogen level(MN)and normal nitrogen level(NN).it is also genotyped with molecular markers for QTL analysis.The main results summarized as follows:1.The ILs were progeny test for phenotypes under DT,LN,MN and NN conditions in Hainan and Shanghai.There existed some variations between experiment locations and treatments.In summary,no significant differences were observed between RP and the ILs in DT performance,however,some ILs in the progeny performed much better DT than the recurrent parent;in three nitrogen levels treatment,ILs performed better than RP in MN and NN,but contrarily in LN.2.Among the grain yield components,plant height and hundred grain weight were closely correlated with grain yield and were much more susceptible to DT.In t nitrogen treatments,plant height,Panicle number and upland weight correlated with grain yield are significant in Hainan;The results in Shanghai were different from Hainan,Panicle number and spikelet fertility percentage in the three fertility levels have reached a significant correlation.100 grain weight reached a very significant negative correlation in MN;the upland weight was significantly positively correlated in LN and MN.3.In the studies on root traitsof two elite lines and Zhong 413,root system of elite lines grew batter than Zhong 413 in the case of adequate water and nitrogen condition;in the drought tolerance and low nitrogen stress conditions,the performance of elite lines is better than the recurrent parent.4.The ILs was genotyped with 117 well distributed polymorphic SSR markers.A total of 35 QTLs were identified through X² test on introgression frequency (P＜0.001),distributed on the whole genome.The additive effects of donor alleles of most QTLs were positive.ANOVA detected many QTLs(GY,HWG and SFP) in DT,LN,MN,NN.Some of which were overlapped to ones mapped by X² test.Most DT QTLs declared in this study were consistent with those documented before.5.With genetic linkage disequilibrium(LD) analyses,681 unlinked but highly LD associated loci was discovered.11 of 15 DT and NUE QTLs correlated with GY composed a genotypic group(GG),which suggested that there might exist the putative genetic network related to DT and NUE.There were Genetic overlaps between DT and NUE.