QTL Analysis Of Related Characters And Nitrogen Use Efficiency Under N-Stress In Maize

Corn is one of the most important food and forage crops in the world,and has an important place in the national economic development.High nitrogen use efficiency in maize had been widely noticed.Breeding hybrid with high nitrogen use efficiency is the most economic and effective approach for increasing nitrogen use efficiency(NUE).Through the inbred line selection for high nitrogen use efficiency,a F_2:3population with high nitrogen use efficiency had been set up in this research,the QTL analysis had first been made on chlorophyll content in ear leaf in maize,plant height dynamic variation under N stress in N-input and no N-input conditions,also the variation of grain and stalk nutrients had been studied simultaneously.The main results as fallows:The changes of chlorophyll content in ear leaf,plant and ear height as well as grain yield have been studied by using 50 maize inbred lines under the low nitrogen stress(LNS)and normal nitrogen fertilization(CK)conditions in this research.The results showed that the chlorophyll content in ear leaf and grain yield dropped on an average by 5.73%and 15.89%,respectively,while the dropping extents varied with inbred lines and highly differences existed among them,ranged about from 0 to 22%for chlorophyll content and 0 to 50%for grain yield.Inbred lines A40,Q3 and Xu178 are insensitive and belonged to high N use efficiency lines to LNS,while the lines of Fengke 1,Shen 99-718,Q2 and Zong 3 are sensitive to LNS.The chlorophyll content in ear leaf can be served as a physiological target for the response of inbred lines to LNS.The unconditional and conditional QTL for chlorophyll contents(CC)at different developing stages were detected under N input(N+)and N stress(N-),using the composite interval mapping method with a 203 F_2:3population derived from an elite maize hybrid Nongdal08(Huang C×Xu178)with high nitrogen use efficiency,and a molecular linkage maps including 189 SSR markers.The results showed that:1)the mean of CC in the five developing stages for parent Xu178 under N- and N+ condition were 54.12 and 55.76,there were 1.80 and 2.40 higher than another parent Huang C,respectively.The mean of CC for the F2:3 populations were 55.6 and 58.32,higher than the mean of their parents,and the variance range for CC was smaller in N+ than N- condition;it implied that the variance range for CC was affected by N- stress in some degree. Under N-/N+ conditions,2,2,1,3,1 and/or 2,2,2,7,1 unconditional QTL for CC were detected at bell stage(BS),florescence stage(FS),early grain filling stage(EGFS),mid:grain filling stage(MGFS)and later grain filling stage(L6FS),respectively,and the accumulative contribution of the detected QTL could explain 22.75%,22.93%,19.77%,49.87%,12.79%and/or 16.95%, 23.49%,19.38%,84.56%,13.38%phenotypic variation of co,respectively.There was one conditional QTL identified for each period from BS to FS,MGFS to LGFS and/or BS to FS,FS to EGFS under N-/N+ condition,it could explain 12.90%,25.51%and/or 15.98%,26.67%phenotypic variance of CC for each period,respectively.The QTL detected for CC expressed in a spatiotemporal model,however qch14 and qch15b were two major QTL identified in different stages and played an import role in maize development.2)N- stress had more influence to plant height in the parent Huang C than in Xu 178,and there was no significant difference in the average of plant height for the F_2:3families between the two nitrogen treatments,but the ranges of variation were different.Under N^- treatment,1,1,2 and 2 QTLs were detected for plant height at elongation stage, small bell stage,large bell stage and grain filling stage,respectively.The total contribution of the detected QTLs could explain 8.42%,13.86%,24..33%and 22.66%of phenotypic variation.Under N+ treatment,there were 1,1,2 and 4 QTLs for plant height in the four different stages above, accounting for 8.10%,12.92%,21.30%and 44.41%of total phenotypic variation respectively.One and five QTLs for plant height were detected from elongation to bell stage and from large bell to grain filling stage under N- treatment,while 1,4 QTLs were detected under N+ treatment,the total contributions of the detected QTLs were 9.14%and 50.98%as well as 13.33%and 44.47%, respectively.About all of the conditional and unconditional QTLs detected appeared to be of dominant and partially dominant effects on plant height.3)N- stress had more influence to the parent Huang C than to the parent Xu 178,and the ear length(EL),ear diameter(ED),row number(RN),kernel number per row(KN)had mainly significant/highly significant positive correlation with grain yield per ear(GY).A total of 53 QTL were identified under N+ and N- conditions in two locations using the composite interval mapping method,including 28 QTL detected in Zhengzhou and 25 QTL detected in Xinzheng.The 53 QTL identified mainly clustered in chromosome 1,2,8 and 9,over 60%QTL appeared to be partial dominant and over-dominant effect.The QTL detected for the six measured traits under N+ condition in two locations were more than the QTL identified under N- condition,and there were 3 and 1 QTL detected under the two nitrogen levels in Zhengzhou and Xinzheng simultaneously.4)The effects of nitrogen(N)on grain yield and three main nutrient components in maize kernels as well as four nutrient components in stalks were investigated.The results suggested that low N stress could raise starch concentration,while it decreased protein content in some degree.Low nitrogen stress would increase acid detergent fiber(ADF)and neutral detergent fiber(NDF)content, and decrease crude protein content and fat content.ADF had significant positive relationship with NDF,and had significant negative relationship with crude fat and protein under two nitrogen treatments in two environments,in contrast,crude fat protein had significant positive relationship with crude protein content.A total of 18 quantitative trait loci(QTL)were detected for grain nutrient traits under two N treatments in both environments,7 QTL for oil content,6 QTL for protein content,and 5 QTL for starch content.The total number of QTL detected for the four measured traits under high N levels was greater than that the QTL detected under low N level conditions,and several QTL specially expressing in different N condition was identified.Twenty five QTL were detected for four measured traits in stalk under two nitrogen treatments in two environments,including six QTL for ADF,four QTL for NDF,ten QTL for crude protein,and five QTL for crude fat.The QTL detected for specially expressing in different N treatments especially the QTL detected only under low nitrogen stress might be relation with high nitrogen use efficiency in maize,which could be aid to understand the genetic basis of N use efficiency.