| Most of important agronomic traits in crops are quantitative traits with complex genetic basis and vulnerable to environmental conditions, which bring some problems for genetic research and plant improvement. QTL analysis and construction of NILs is the basic premises for fine mapping and positional cloning of quantitative trait loci . In this study, based on Maize Hybrid Nongda108 and its F2: 7 family lines, Field trial had been made to study the effects of N treatment on the ear traits of maize under nitrogen supply(N +)and no-nitrogen supply(N-) conditions in Xunxian and Zhengzhou, and the concerning QTL were analyzed using composite interval mapping method (CIM). Five objectives QTL - NIL including chlorophyll content, kernel weight, protein content, ear diameter, plant height were constructed by Marker-Assisted Selection according to the primary QTL identified in F2:3 population. The main results of this study are:1)Using Huang C, Xu178 and its RIL population, a maize genetic linkage map were constructed, containing 217 dominant SSR markers, covering 10 chromosomes , and with a total length of 2434.2 cM, and average interval length of 11.2cM between markers.2)A total of 16 QTL associated with ear traits in maize were detected in Xun Xian. The result showed that 7 QTL were detected under N- condition and 9 QTL under N+ condition,mainly distributed on chromosomes 1,7 and 10,and each QTL could explain 7.56%~24.41% of phenotypic variation. QTL ,RN10a and RN10b were identified for Row number(RN) on chromosome 10 bnlg1185-umc2021 and bnlg1450-bnlg1185 interval ranges,respectively. Also ,different QTLs controling different traits were detected in same regions , such as axial diameter (qAD7a) and 100 kernel weight (qKW7) are located on the range of mmc071~umc1545 marker on chromosome 7 under no nitrogen supply condition;while Ear length (qEL1) and ear diameter (qED1) are located on the same range of phi227562-bnlg504 on chromosome 1 under nitrogen supply condition.This may be the result of pleiotropism.3)A total of 14 QTL account for ear traits in maize were detected in Zheng Zhou. The result showed that 8 QTL were detected under N- condition and 6 QTL were detected under N+ condition. The QTL mainly lied on chromosomes 1,5 and 6 ,and each QTL could explain 8.31%~17.42% of phenotypic variation. under no nitrogen supply condition, the ear diameter, ear weight and grain weight QTLs were all detected within the same interval of umc1912-phi452693 marks on chromosome 6, and the contribution of each single QTL was between 12.32% -15.42%, It may also be the result of pleiotropic effects.4)According to the primary QTL identified in F2:3,qChl4 was in the interval between umc1395～umc2237 and allele from the nitrogen efficiency inbred line A51 contributing to increase in Chlorophyll content, Which was 4.01 ~ 4.02 bin sites, spacing 19.8 cM, LOD value of 4.27, the contribution rate of 17.15%.Using A65, a nitrogen-sensitive inbred line, served as the recipient and recurrent parent. Following the strategy of NIL development by consecutive backcrossing, a NIL for Chlorophyll content was constructed in A65 background. 70 SSR markers were used in genetic background selection. The average interval of markers on chromosome was 25.37cM and 97.27% of Recovering Ratio of Genetic Background (RRGB) in BC3F1.That can be regarded as near isogenic line qChl4. Similarly 4 target QTL NILs of kernel weight, protein, ear diameter, plant height were also built, the RRGB of BC3F1 generation selected plants were 96.31%, 97.25%, 96.36% and 95.45%,respectively. The target QTLs could be further detected and as a basis for fine mapping using BC3F2 segregating population composed by NILs. |
