Flag leaf is an important place for wheat photosynthetic carbon fixation, which plays an important role in wheat yield. The genetic characteristics and the genetic mechanism were analyzed under high and low nitrogen for flag leaf traits of wheat, which will provide a reference for excellent plant-type breeding and high-yield breeding.

188 recombinant inbred line (RIL) populations derived from a cross between Kenong9204 and Jing411 was used in this study, which were planted in low nitrogen (LN) and high nitrogen (HN), respectively. The flag leaf traits of 188 RILs were investigated in 6 different environments, then the genetic analysis was conducted to determine the number of genes controlling each trait, and to estimate the genetic effect value and the heritability. In addition, the relationship between flag leaf characters and yield related traits of wheat was also studied.

Under LN environment: The optimal genetic model of flag leaf length was 2MG-CE (two pairs of interaction major genes) in E3. The additive × additive epistatic interaction value was 1.098, and the heritability of major genes was 31.35%. The flag leaf length was polygenic in another LN environment. The width of flag leaf was polygenic in all the LN environment. The optimal genetic model for flag leaf area (except E5) was 2MG-CE. The additive × additive epistatic interaction value was 1.884 and the heritability of major genes was 36.7%, while it was polygenic inheritance in E5. Under HN environment: The optimal genetic model for flag leaf length (except E4) was 2MG-CE, the additive × additive epistatic interaction value was 1.133, and the heritability of major genes was 32.6%. The optimal genetic model was 2MG-ER (two pairs of recessive epistatic major genes) in E4, which the additive effect value was 1.431 and 1.108 for the first and the second major genes respectively, and the heritability of the major gene was 51.77%. The optimal genetic model for flag leaf width (except E2) was 2MG-CE, the additive × additive epistatic interaction value was 0.119, and the heritability of major genes was 37.29%, while it showed polygenic inheritance in E2. The optimal genetic model for flag leaf area was 2MG-CE, which the additive × additive epistatic interaction value was 3.067 and the heritability of the main gene was 44.42%. The genetic models of flag leaf traits were different in different environments, which the genetic model was more stable under HN than that in LN. The correlation analysis of flag leaf and yield traits showed that flag leaf traits were significantly positively correlated with grain number per spike, grain weight per spike and yield per plant, and the influence degree was different in the 6 environments.

Flag leaf traits are easily affected by environment, and the performance of flag leaf traits is different in HN and LN. Flag leaf traits exhibited different major gene inheritance and polygene inheritance in LN, while they showed major gene inheritance which controlled by two pairs of interactions genes in most of HN environment, which might be major QTLs. Yield per plant and grain weight per spike could be increased by improving flag leaf traits.

By analyzing the genetic and breeding selection effects of the stable major QTL for spike length in wheat, its genetic effects on yield-related traits were clarified, and the future breeding application potential was evaluated. The results could provide a basis for subsequent gene mining and molecular breeding of wheat.

A major QTL for spike length, named qSl-2D, was detected in multiple environments using a recombinant inbred lines population derived from the cross of Kenong9204 and Jing411, denoted as KJ-RIL; Two molecular markers closely linked to qSl-2D were developed by using the InDel sites in target interval. The genetic effects of yield-related traits based on KJ-RIL, MY-F₂, NILs and natural mapping populations, were analyzed by combining genotype data of molecular markers or wheat 55K array, respectively. By genotyping the natural mapping population, the breeding selection effect of qSl-2D haplotype was parsed across different wheat regions and different ages.

QTL mapping results showed that qSl-2D could be detected in 7/10 sets of environmental data, and could explain 4.02%-10.10% of the phenotypic variation. The peak LOD of 5/10 sets of environmental data was positioned at 608.75 Mb. The results of genetic effect analysis showed that the enhancing allele of qSl-2D could significantly increase spike length in the four populations with different genetic backgrounds. In addition, it has positive effects on kernel number per spike and plant height, but has negative effects on thousand kernel weight, kernel weight per spike and yield per plant in most population backgrounds. Further analysis of plant height in KJ-RIL population showed that the enhancing allele had rod lowering effect on all internode lengths except the internode length below spike, which resulted in the insignificant increase in plant height. The results of qSl-2D haplotype analysis showed that the utilization rates of the long-spike haplotype Hap-AA-GG varied greatly in different wheat regions, with the highest utilization rate in the northern winter wheat region, accounting for 24%; while the short-spike haplotype Hap-CC-CC accounted for more than 30% in most wheat regions. Moreover, the utilization rate of qSl-2D long-spike haplotype showed a gradual decrease over time, while that of short-spike haplotype consistently maintained a higher selection trend.

A stable major QTL-qSl-2D for spike length was identified, the enhancing allele of qSl-2D could significantly increase spike length under different genetic backgrounds, and had certain genetic effects on yield-related traits. The closely linked molecular markers developed in the target region can be used for the genetic improvement of wheat spike length and yield-related traits in wheat.

1BL·1RS translocation lines are widely used in wheat breeding programs. The genetic effects of 1BL·1RS on yield and quality related traits will be characterized under different backgrounds, and its application in breeding programs will be evaluated. The study will provide therotical references for the selection of high-yield and high-quality wheat varieties.

The natural mapping population comprised by 244 varieties/advanced lines and the 188 recombinant inbred lines (KJ-RIL-F₈) derived from the cross between Kenong9204 (KN9204) and Jing411 (J411) were used in this study. Their genotypes were detected by the 1RS diagnostic markers. Combining with the phenotypic values, the genetic effects of 1BL·1RS translocation on yield and quality were characterized. The selection and utilization of 1BL·1RS translocation in breeding programs were clarified by analyzing its proportion in the approved varieties among different decades and cultivate locations.

Of the 188 KJ-RILs, 74 were 1BL·1RS translocation lines. The yield-related traits analysis showed that, under both high and low nitrogen conditions, the 1BL·1RS translocation lines significantly prolonged the heading date, increased grain nitrogen content ratio, increased flag leaf length and flag leaf area; while it significantly reduced kernel number per spike. The 1BL·1RS translocation had no significant effect on the spikes number per plant, thousand kerner weight or flag leaf width. Under both high nitrogen and low nitrogen conditions, 1BL·1RS translocation could significantly increase water absorption rate, wet gluten content, protein content and grain hardness; it had no significant effect on testweight, tractility or sedimentation value. Of the 244 varieties/advanced lines in the natural population, 76 were 1BL·1RS translocation lines. The 1BL·1RS translocation could significantly increase kernel number per spike, spike length and spikelet number, but it could significantly reduce plant height. However, it had no significant effect on spikes number per plant, thousand kerner weight, flag leaf length, flag leaf width or flag leaf area. The 244 varieties/advanced lines in the natural mapping population were classified and grouped according to wheat cultivation locations and variety certification time. The results showed that there were significant differences in the proportion of 1BL·1RS among different wheat cultivation locations. The proportion of the 1BL·1RS translocation lines began to increase from the 1990s in breeding programs.

There is no significant difference for the effects of 1BL·1RS translocation on yield and quality traits under high and low nitrogen conditions. The 1BL·1RS translocation showed inconsistent effects on yield related traits in the KJ-RIL mapping population and the natural mapping population, probably due to the different genetic backgrounds among them.