Construction Of Genetic Linkage Map And QTL Analysis For Important Agronomic Traits In Wheat Introgression Lines

Wheat is the most important food crop in the world, so to breed high yield and quality wheat varieties is one of the main tasks for wheat breeding. Most of agronomic traits of wheat are quantitative traits and are related to yield traits. QTL mapping of important agronomic traits using introgression line population and discover important genes established foundation not only for fine mapping and map-based cloning, but also for the polymerization breeding. The objective of this study is to construct a genetic linkage map of wheat and make a QTL analysis for important agronomic traits, including heading date, plant height, first internode length, length from flag leaf pulvinus to spike base, spike length, number of valid tiller, fertile spikelet number of per main spike, grain number per main spike, grain weight per plant and thousand grain weight, using a 160 population of introgression lines derived from Lumai14/Jing411. The main results are as follows:1. A total of 565 SSR markers were used to analyze the polymorphism between parents. A number of 156 loci were identified polymorphism, which represented 27.61% of effective amplification reaction. The genetic background of Lumail4 was 93.2% in this IL access to its theory value 93.8% by genotype detection. According to the international wheat consensus SSR map,156 markers were anchored in the linkage map of the IL. The number of polymorphic markers ranged from 3 to 15 on each chromosome. And every chromosome contained 7.42 markers in average. The average length between two markers was 16.47 cM. Among them, the chromosome 3B contained 15 markers, while the number of markers on the 4B and 5D were only 3. Among the 156 polymorphic markers,125 markers were polymorphic in IL population, which accounted for 80.13% of polymorphic markers. All of the ILs contained substitution fragment from donor parent Jing411 in 160 lines. Two to twenty-five introgression segments were detected in every line, average of 6.85 in each line. The length of the donor fragment ranged from 23.12 cM to 516.37 cM, and the average length was 133.7 cM, accounting for 0.90%-20.10% of genome coverage percentage.2. Chi-square test was conducted on gene frequency of 125 polymorphic molecular markers in the IL population. There were 99 markers significantly distorted from the expected segregation, accounted for 79.2% loci in statistics, and they were distributed on all 21 chromosomes. In these segregation distortion markers,57 loci deviated toward Jing411, while the remaining 42 markers biased towards Lumai 14. A total of 12 distortion segregation hotspot regions were detected on 11 chromosomes 1A, 1B,3A,4D,5D, 6B,7B and 7D.3. Phenotypic analysis of 10 important agronomic traits in ILs showed that coefficients of variation for all traits ranged from 0.40% to 60.25% under four different environment conditions, and the mean values of most of traits presented the tendency to be more adjacent to the recurrent parent Lumai14. As can be seen from the range of phenotypic variation, apart from HD under El and E4, FNS under all environments as well as GWP under E4, the majority of traits displayed bidirectional transgressive segregation phenomenon. But all characters exceeded recurrent parent Lumai14, probably owing to the introgression of favorable alleles from non-recurrent parent Jing411.4. A total of 33 additive QTLs and 229 pairs of epistasis QTLs for important agronomic trait in wheat on all chromosomes expect 5D were identified. The additive QTLs for 2 agronomic traits were simultaneous located next to the markers Xwmc24(1A),Xwmc707 (4A) and Xwmc331 (4D).Some additive QTLs and epistasis QTLs simultaneously controlled multiple traits distributed on close to the markers Xwmc128(1B),Xgdm126(1D),Xgwm60(7A),Xwmc517(7B) and so on. Among these QTLs, QSl-1D-1 controlled spike length was detected under E1 and E3, both QFns-7B for fertile spikelet number of per main spike and QTgw-7B-1 for thousand grain weight were identified under E1 and E2 two different water regimes, which were stable expressed QTLs. QTLs detected near the Xwmc707 on chromosome 4A controlled first internode length and length from flag leaf pulvinus to spike base together under E3 and E4, besides FIL positively correlated with LPSB significantly, which maybe a pleiotropic or tightly linked QTL. Because the numbers and the phenotypic variation contribution rate of epistasis QTLs were more and lager than additive QTLs, what’s more, most of additive QTLs were involved in the interaction of epistatic QTL, which indicated that epistatic effect played a major role on important agronomic trait of wheat.5. The QTLs controlling important agronomic traits in wheat located regionaly on different chromosomes or on the same chromosome, which formed hot spot regions, including 5 additive QTLs and 60 epistatic QTLs. Among them, the hot-spot regions located close to the region in Xwmc24(1A), Xwmc312(lA), Xgdm126-Xcfd63(1D), Xwmc707(4D), Xwmc524(5A), Xwmc740(5B), Xbarc96(6D), Xwmc809(7A), Xwmc517(7B) and so on, became important hot-spot regions controlling target trait of wheat, which illustrated these chromosome segment carried a large number of target genes.In this study, a wheat IL population generated from Lumai14/Jing411 was used as plant materials. The genetic basis and expression pattern of important agronomic traits in wheat were analysed in the respect of molecular, which provided a theoretical basis for the genetic improvement of wheat. Stable expressed QTL and pleiotropic or tightly linked QTL had important significance in QTL-NIL building, QTL functional research and map-based cloning.