The Genetic Analysis For Responses To Nitrogen Stresses Using Rice Chromosomal Segment Substitution Lines

Rice production has mainly relied on the increase in nitrogen fertilizer in recent decades.Surplus application of nitrogen fertilizer has brought a series of environment problems.Study on the genetic mechanism of nitrogen utilization is the main way to solve these problems.In this study,we analyzed the genetic components associated with tolerance to low nitrogen in rice at seedling stage and mature stage,using a population of 127 chromosomal segment substitution lines(CSSLs) from a cross between indica cv. 93-11 and japonica cv.Nipponbare.The CSSLs were cultivated in low nitrogen(N-) and normal nitrogen(N+) using plastic pods.Seedling height,tiller number,shoot dry weight and root-related traits(root number,total root length,average root length,longest root, root dry weight) at seedling stage,and dates to flowering,SPAD value at heading date, plant height,yield-related traits(panicle length,productive tillers per plant,number of primary branches,seed setting ratio,filled grain number per panicle,grain yield per plant and biomass(root dry weight,over ground dry weight,plant dry weight) were investigated at mature stage.The main results are as follows:1.Except for root/shoot ratio,the average performances of measured traits for parents and the CSSLs are lower under low nitrogen level as compared that normal nitrogen level,of which yield per plant and biomass have significant differences between the two levels,again indicating that the CSSLs were very sensitive to the low nitrogen stress.2.Yield per plant were significant(p＜0.05) or extremely significant(p＜0.01) correlation with seedling height,tiller number and rooting capacity(root number,root weight and total root length) at seedling stage under the two nitrogen levels,indicating that seedling development has a great impact on yield in rice.Significant negative correlation between relative traits and its measurement under normal nitrogen condition suggests a general trend in the CSSLs,that is,better performance of line, lower tolerance to the stress.3.Harvest index(HI) between 9311 and Nipponbare was great different,the HI value of 9311 was about 0.42-0.53 under two nitrogen conditions,while Nipponbare about 0.16-0.25.It indicates that the process of nitrogen or other substance distribution may be different.The information of QTLs for HI could be usful for further understanding its genetic mechanism and for development of high yielding varieties. 4.One hundred and sixty four QTLs were detected for the measured traits under two nitrogen levels,which distributed on 12 rice chromosomes.A majority of QTLs under the two levels were different,and the most were also different from those QTLs detected for relative traits.The results indicate that absorption and utilization of nitrogen under various nitrogen levels might be regulated by different genes.5.Many colocations of QTLs such as the same region including three or more QTLs for various traits were detected.The reason may be tightly linked genes influencing more traits independently or pleiotropy(the same genetic factor controls both traits).Some of the colocation QTLs did adjacent to the known genes in nitrogen metabolic pathway,suggesting these QTLs may be involved in process of nitrogen absorption, transportion and utilization.In addition,most of the colocation QTLs regions or hot regions haboring QTLs for yield per plant,suggest that yield per plant is regulated by expression of many genes in whole rice growth.The results will provide some significant information for further revealing genetic bases of efficient use of nitrogen.