Construction Of Maize SSR Linkage Map And QTL Analysis Of Agronomic Traits Under Two Nitrogen Levels

In the world wide, most of maize was planted in poor soil, and nitrogen is one of most important nutrition elements for maize growing, especially for maize yield. However, a great deal of nitrogen is applied in soil, which would induce higher costing, lower nutrition absorption rate and environment pollution. To solve the above problems special maize varieties with resistant to low nitrogen stress should be developed through maize breeding program. Firstly, the collection and evaluatiion of relevant genetic resources is one of key factors in breeding. So, extension of maize germplasm and QTL analysis of maize nitrogen absorption rate is very stringent for improving maize nitrogen absorption rate by molecular marker assistant selection. In this research, a SSR linkage map was constructed by using F₉ RIL (recombinant inbred line) population which derived from Mo17×Huangzao4. The QTLs of controlling maize main agronomic traits were also mapped. The main results are as follows:1. A SSR linkage map was constructed by the F₉RIL population derived from the cross combination of inbred Mo17 and inbred Huangzao 4, which covered the whole genome of maize.there was about 1364.3 cM along all the linkage group and averagely 13.92 cM between markers. It indicated that my map was almost consistent with published IBM linkage map and was suitable for QTLs location.2. 17 traits investigated in the field trial such as yield, plant morphology and mature of Mol7, Huangzao 4 and 239 RILs under high and low nitrogen levels. ANOVA and correlation analysis indicated that the difference under the two levels were significant at 0.01 signifcant level and the correlated relations among the 17 traits were very complicated. The absolute value of kurtosis and skewness of the 17 traits under the two nitrogen levels were computed and the results showed all 17 traits were complied with normal distribution, and QTL analysis could be carried out on these traits.3. The QTLs of 17 traits and low nitrogen tolerance index of yield (NTIY) under high and low nitrogen levels were detected by composite interval mapping(CIM) method. The total number of QTLs were 92, including 31 QTLs under high nitrogen level, 58 QTLs under low nitrogen level and 3 QTLs for NTIY, but no QTLs for controlling Days-to-Seedling were detected. All the detected QTLs were distributed in 43 intervals on 10 chromosomes.4. 15 QTLs controlling Growth-Stage were detected. Under high nitrogen levels 5 QTLs controlling ASI were found, in which 2 QTLs were on chrososome3, and the rest distributed chromosome 6, 7 and 8, respectively. These QTLs accounted for 4. 89%-9. 36% of phenotypic variance. Under low nitrogen levels, 4 QTLs were detected for Days-to-SiIking, in which 2 QTLs distributed on chromosome 6 and 2 on chrhomosome 9, all of 4 QTLs could totally explain 53. 62% of phenotypic variance. 3 QTLs were detected for Days-to-anthesis, which all distributed on chromosome 9 and could account for 9. 29%—12.24% of phenotypic variance. 3 QTLs were detected for ASI, which distributed on chromosome 6, 7 and 8, respectively and accounted for 30. 09% of phenotypic variance. For growth stage the QTLs with additive effect could contribute to prolong Days-to-Anthesis, Days- to-Silking and ASI.5. 33 QTLs for plant morphology trait were detected. Under high nitrogen level, 2 QTLs controlling plant height were found, which distributed on chromosome 1 and 9 and accounted for 17. 94% and 5.27% of phenotypic variance, respectively. 3 QTLs for Ear-Leaf-Area distributed on chromosome 2,4 and 6, respectively, which accounted for 16.75% of phenotypic variance.1 QTL controlling width of ear leaf distributed chromosome 1, which accounted for4. 98% of phenotypic variance. 1 QTL for length of ear leaf distributed chromosome 2, which accounted for 5.05% of phenotypic variance. 2 QTLs controlling ear position distributed on chromosome 1 and 9, which accounted for 9. 55% and 13. 11% of phenotypic variance, respectively. The detected QTLs under low nitrogen level with nearly same location and additive effect as high nitrogen levels were as follbws: 2 QTLs for plant height. 4 QTLs for ear leaf area distributed on chromosome 4, 6, and 7, which accounted for 5.57-12.34% of phenotypic variance. 2 QTL for width of ear leaf distributed on chromosome 1 and 9, which accountedforl7. 48% of phenotypic variance. 5 QTLs for length of ear leaf distributed on chromosome 4, 6 and 8 , which accounted for 44.41% of phenotypic variance.5 QTLs for ear position distributed on chromosome 1 and 9, which accounted for 48. 83% of phenotypic variance. 6 QTLs for leafs per plant distributed chromosome 3,6,7 and 9, which accounted for 55.86% of phenotypic variance.6. 41 QTLs controlling yield and its component factors were detected. Under high nitrogen level, 5 QTLs of ear rows distributed on chromosome 4,9 and 10, which accounted for 52. 59% of phenotypic variance. 2 QTLs of ear diameter distributed on chromosome 9 , which accounted for 17. 38% of phenotypic variance. 1 QTL of ear length distributed on chromosome 1, which accounted for 10. 55% of phenotypic variance. 5 QTLs of kernel per row distributed chromosome 1,2 and 6, and which accounted for 54. 27% of phenotypic variance . 1 QTL of kernel ratio distributed on chromosome 9, which accounted for 4. 30% of phenotypic variance. 1 QTL of 100-kernel weight distributed on chromosome 7, which accounted for 6. 81% of phenotypic variance. 2 QTLs of grain yield distributed on chromosome 9, and which accounted for 5.83% and 8.75% of phenotypic variance, respectively. For low nitrogen level, 4 QTLs of ear rows distributed on chromosome 4 and 9, which accounted for 59.99% of phenotypic variance. 4 QTLs of ear diameter distributed on chromosome 4 and 9, which accounted for 44. 12% of phenotypic variance. 4 QTLs of ear length distributed chromosome 1 and 5, which accounted for 50.28% of phenotypic variance. 5 QTLs of kernel per row distributed on chromosome 1, 2 and 6, which accounted for 62.55% of phenotypic variance. 1 QTL of kernel ratio distributed on chromosome 9, which accounted for 9. 38% of phenotypic variance. 5 QTLs of 100-kernel weight distributed on chromosome 3, 4, 7, 9 and 10, which accounted for 47.66% of phenotypic variance. 1 QTL of grain yield distributed chromosome 1, and which accounted for 7.61% of phenotypic variance.7. The low nitrogen tolerance index of yield (NTIY) was defined. 2 QTLs of low nitrogen tolerance index of yield were detected on chromosome 4 and 9, which accounted for 7.49% and 8. 15% of phenotypic variance of yield, respectively, and their additive effects were -5.73 and -5.85, respectively. Both of allelelocus with positive effects derived from male parent. The results agreed that Huang-zao 4 is resistant to poor soil. New QTLs with resistance to low nitrogen stress distributed on chromosome 4. The location of NT1Y and QTLs of yield were repetitive on chromosome 9.8. All detected QTLs were very unevenly distributed on the 10 linkage groups, e. g. the number of QTLs on the ninth linkage group summed to 24. And these QTLs distributed on chromosome with clustering character, e.g. 7 QTLs of the ninth linkage group were detected in the intervals between ncl34 and PhiO67 and between Umcl357 and Bnlgl375, respectively.