Rules Of Ear Bearing And QTL Mapping For Spike Numbers Per Plant In Coordination-type Wheat

Common Wheat (Triticum aestivum L.), belongs to Gramineae, having the characteristics in tillering and ear bearing, and is also one of the most important food crops in the world. Increasing in the production of wheat is the most important goal of wheat breeders. Grain numbers, spike numbers and grain weight usually consider as the three factors of wheat yield. Coordination-type wheat has higher spike numbers as well as maintains large grain weight, effectively coordinating the relationship between spike numbers and grain weight. Meanwhile, it also possesses the important traits like disease resistance, high and stable yield, good quality, etc. In this study, we used coordination-type wheat cultivar Chuannong 18, which is a 1RS.1BL translocation line and a 1RS.1BL translocation line 1208 as parents to construct a recombinant inbred line (RIL) population, and carried out the statistical analysis of the rules of ear bearing and QTL mapping for spike numbers per plant. It is expected to lay a foundation for marker-assisted selection breeding of wheat, in order for further development of wheat production potential, and to break through the existing ecological ear capacity in Sichuan area. The main results are as follows:1. The RIL population (F11) which was constructed by coordination-type wheat cultivar Chuannong 18 and a translocation line 1208 as parents displayed continuous variation in the quantitative traits which are tiller numbers and spike numbers per plant, and it was a significant positive correlation between maximum tiller numbers and effective spike numbers per plant, and the Pearson correlation coefficient is 0.752. In this population, the range of maximum tiller numbers was 6.9-20.2, the range of spike numbers per plant was 4.4-12.4, and the range of effective spike rate of tiller was 0.40-0.85. Some strains in the population have the high capacity of tillering and ear bearing.2. A total of 1157 SSR molecular markers were screened in the parents resulting in 138 polymorphic molecular markers between parents accounting for 11.9% in a total number of molecular markers. Out of these,110 markers are used for genetic constructing linkage map by the software QTL IciMapping V3.2, which covering 19 chromosomes of wheat, except two chromosomes 1A and 7B. Out of these,23 markers were located in genome A,53 markers were located in genome B and 34 markers were located in genome D. The most molecular markers were located in genome B and covered a length of 1804.01 cM, and the average genetic distance was 34.04 cM.3. Grouping the population as follows:the low tillering group (5-10 seedlings), the middle tillering group (11-15 seedlings) and the high tillering group (16-23 seedlings); the low ear bearing group (4-6 ears), the middle ear bearing group (7-9 ears) and the high ear bearing group (10-12 ears). Correlation analysis between each group and screened polymorphic markers, out of those molecular markers Xbarc74, Xbarc156, Xbarc232, Xgwm533 were significantly positive correlation to the both traits of maximum tillering and ear bearing.4. Using Inclusive Composite Interval Mapping (ICIM-ADD) method in the software QTL IciMapping V3.2 for QTL analysis in the RIL population of the tiller numbers and spike numbers per plant, keeping LOD> 2.5 as threshold, a total of 24 additive QTLs were detected in 1B, 1D,2A,2B,3D,4B,4D,5B,7A and 7D, respectively. Out of these,14 QTLs for tillering could explain 9.16%-37.81% of phenotypic variation, 2 QTLs for ear bearing could explain 12.42%-16.4% of phenotypic variation, and 8 QTLs for effective spike rate of tiller could explain 8.2%-8.2% of phenotypic variation..5. Using Inclusive Composite Interval Mapping (ICIM-EPI) method in the software QTL IciMapping V3.2 for additive × additive epistatic QTL analysis, a total of 10 pairs of additive×additive epistatic QTL were detected having high LOD values (LOD>5.0), and explaining 10.12%-51.4% of phenotypic variation. Out of these,9 pairs of additive × additive epistatic QTL between two random sites were detected,6 pairs of which were for tillering, and 3 pairs were for spike numbers per plant. Only 1 pair of additive × additive epistatic QTL was detected between a random site and one additive QTL, located in 2B chromosome explained 39.98% of phenotypic variation, and the epistatic effect was greater than additive effect. In the entire growing process, gene epistatic effect for tillering and ear bearing in turn was:tillering from mid-winter to early spring> ear bearing per plant>early tillering.