Analysis Of QTLs Associated With Drought Resistance Traits In Wheat

Wheat (Triticum aestivum L.) is one of the most important foodstuff crops around the world. Drought is one of the most important abiotic constraint limiting the yield of wheat. The advent of increasing water scarcity in this century, investigating genetic basis and expression rules of physiological and morphological traits involved in drought resistance is of significance not only on further understanding the molecular mechanism of drought tolerance, but also developing practical selection markers and molecular marker-assisted drought toleranc breeding.A doubled haploid (DH) population with 150 lines, derived from a cross between two Chinese common wheat varieties Hanxuan10 and Lumai14 was employed under the drought stress (DS) and the well-watered (WW) conditions. Paraffin sections were made from the middle part of the first internodes, which were sampled on 14th~15th day after flowering. The number and area of vascular bundle were observed. The chlorophyll contents were detected under DS and the WW conditions at the heading, flowering and grain-filling stage, respectively. The parameters of chlorophyll fluorescence kinetics (PCFK), at heading stage, grain-filling stage and maturity stage were measured, respectively. Under DS and WW, the relative-content of stem water-soluble carbohydrates, absolute-content of stem water-soluble carbohydrates and remobilization capacity of stem water-soluble carbohydrates were obtained. The objective was to map QTLs associated with these traits, dissect genetic character of these traits and their QTL expression pattern under DS and WW. The detailed results are as following.(1) Drought stress restrains badly the development of vascular bundle, such as areas of large, small and total vascular bundle, and the numbers of small and total vascular bundle. Number and area of vascular bundle were significantly correlated with yield components of spike. A total of 38 QTLs with additive effects were detected for vascular bundle and yied components under two water regimes. Additive QTLs individually explained 4.15% to 46.61 % of the phenotypic variations. Many QTLs for the number of vascular bundles were localized to the same marker or marker interval. For example, the flanking markers P8922-175~P8222-380 on chromosome 4A and the flanking markers P6901-280~P1142-155 on chromosome 6B were shared by the additive QTLs for the numbers of large vascular bundle and small vascular bundle. The additive QTLs for fertile spikelet and fertile spikelet rate were identified at the same interval of Xgwm391~P8422-17 on chromosome 3A. The cluster distribution of QTL for vascular bundle and yield components were genetic basic for their high phenotypic correlation.(2) Drought stress reduced the chlorophyll content (ChlC). A total of 14 additive QTLs controlling ChlC were detected at three stages under two water regimes. The contributions of additive QTLs to phenotype variation were from 5.53% to 23.50%. QTLs clustered on chromosome 2B, 5A and 7A, especially on chromosome 5A, on which 5 additive QTLs were detected. Additive QTLs QChlc.cgb-2B, QChlc.cgb-7A-2 and QChlc.cgb-5A were detected at two stages simultaneity.(3) PCFK, such as Fm, Fv, Fv/Fm and Fv/Fo, were sensitively decreased while wheat suffered from drought stress, but Fo can swiftly increase. Total of 33 major-effect QTL (H2(A)>10%) were identified, and 30 of them were located within a 4.0 cM interval flanked by adjacent markers. The QTLs for PCFK were mapped on the near or same chromosomal region, and mainly congregated in cluster on chromosome 1A, 1B, 7A and 7B.(4) Drought stress could not only increase relative-content of stem water-soluble carbohydrates (RCSWSC), absolute-content of stem water-soluble carbohydrates (ACSWSC), but also can lead to faster remobilization efficient of pre-stored carbon from vegetative tissues to the grains. There was high significant positive correlationship between the remobilization efficiency of pre-stored carbon and the intensity of grain-filling. Some QTLs for RCSWSC and ACSWSC were detected in same or near region (co-location) of chromosomes at two stages, for example, the intervals with flanking markers WMC474～Xgwm374～WMC474 on chromosome 2B, WMC291～P3156-185 on chromosome 3B and P3470-210～WMC269.3 on chromosome 6B. These QTLs for content of stem water-soluble carbohydrates and remobilization capacity of stem water-soluble carbohydrates were cluster in chromosome 2B,3B,6B and 5A .Results of the research provided a molecular and genetic basis for understanding the drought-tolerant mechanism and developing practical markers in molecular breeding drought-tolerant cultivar in wheat.