| The impact of drought on wheat(Triticum aestivum L.) production is becoming more serious, especially in the grain filling stage; studying drought resistance and developing drought-resistant varieties have become the target of plant breeders; stay-green, an important crop drought-resistant mechanism, is closely related to drought resistance and high temperature resistance, and it is found in a variety of plants, which can prolong the effective time of photosynthesis and effectively preventing premature aging, which is of great significance for improvement of biological yield and grain yield. Crops stay green is a complex biological phenomenon, characterized by quantitative inheritance; Using molecular marker genetic linkage analysis to obtain some stable markers closely associated with the stay-green gene can be the basis of MAS and Map-based cloning.In this study, a doubled haploid (DH) population with150lines, derived from a cross between two Chinese common wheat varieties HanxuanlO and Lumail4, was employed under the drought stress (DS) and the well-water (WW) conditions. To model senescence and identify quantitative trait loci (QTL) for stay-green related traits, the DH lines and parents were evaluated for stay-green traits, such as green leaf area duration (GLAD) and green leaf number of main stem (GLNMS), from10days after anthesis (DAA) until maturity. A non-linear regression curve was fitted on the green leaf area data using a Gompertz statistical model, and the maximum rate of senescence of flag leaf (MRS)、the day that plant begin to senescence (Ts)、 the day that plant senescence (To) and other aging characteristic traits were calculated; Meanwhile, the correlation between stay-green related traits and yield-related traits was analyzed; genetic analysis and QTL mapping for above-mentioned traits revealed the mechanism of drought resistance and provide the basis for breeding stay-green varieties. The results are as follows:Under two water regimes, the correlation of GLAD (22,25,28and31days after anthesis) and GLNMS (20,25, and30days after anthesis) were significantly or highly significantly positive, the correlation analysis results showed that the GALD had significant or highly significant positive correlation with75%green,50%green,25%green, percent greenness at maximum senescence (PGMS), Ts and To, and the GLAD was negatively significant correlated to MRS. All the observation period after anthesis, the GLNMS had significant positive correlation with75%green,25%green, TMRS, Ts and To, but no significant correlations were detected between GLNMS and PGMS,50green; there were significant or highly significant negative correlations between the GLNMS (20,25, and30days after anthesis) and MRS. The results of correlation analysis about senescence related traits were approximately same:the MRS had highly significant positive correlation with the day that plant begin to senescence (Ts), and the significant or highly significant negative correlation was observed between MRS and other senescence related traits.Under two water regimes, there were significant positive correlations between GLAD of flag leaf and grain weight, and no significant correlation between the GLAD and yield per plant (YPP); under drought stress (DS), the significant positive correlation was observed between GLNMS and1000-grain weight in later grain filling stage, but no significant correlations were detected between GLNMS and TKW and between GLNMS and YPP under well-water (WW); Under two water regimes, the MRS had significant positive correlations with1000-grain weight and yield per plant, the yield traits were significantly or highly significantly positively correlated to Ts,75%green and50%green, and no significant correlations were detected between yield traits and other senescence related traits.The stay-green related traits phenotypes showed a wide variation and transgressive segregation among the DHLs, all those stay-green related traits exhibited complex quantitative genetic features, which were controlled by minor-effect polygenes, QTL mapping can reveal the genetic mechanism. A total of50additive and49pairs of epistatic QTLs for stay-green related traits were detected, additive QTLs were mainly distributed on1A,1B and5A chromosomes, total of29major-effect QTL (H2(A)>10%) were identified, accounted for58.00%of the total additive QTL detection. A total of14additive and6pairs of epistatic QTLs were detected for TKW and YPP, and the additive QTLs were distributed on1A、1B、4A、5A、6A、6D and7A chromosomes.The QGlnms20-1A-1under well-water (WW) and the QTmrs-1A, QTs-1A, QTo-1A, Q25%G-1A under drought stress (DS) were co-localized in the interval P3615.2-WMC336on chromosome1A; under well-water, the QGlad22-1B-1,QGlad25-1B-1and QTkw-1B-1were localized with markers Xgwm273-Xgwm131on chromosome1B; the QTL for GLAD:QGlnms10-1D-1, QGlnms15-1D-1under well-water and QGlnms10-1D-2under drought stress (DS) were localized with marker WMC432on chromosome1D; the markers WMC410-WMC74-Xgwm291-Xgwm410on chromosome5A span a QTL region for the SG traits under two water regimes, and the QGlad22-5A-2, QGlad25-5A-3, Q75%G-5A and QTkw-5A-1were detected under well-water, the QGlnms25-5A, QTmrs-5A, QTo-5A and Q25%G-5A were detected under drought stress (DS); Meanwhile, under drought stress (DS), the QGlad22-5A-1, QGlad25-5A-1, QTs-5A and Q75%G-5A-1were detected in the interval WMC524-Xgwm595on chromosome5A; other QTLs of GLAD and GLNMS were detected in a specific period and environment, showed specific expression. Major and minor QTLs for all target traits showed disequilibrium distribution among different chromosomes and even different intervals on the same chromosome. These QTLs assembled in some specific interval formed the hot-spot region for regulating inheritances of corresponding traits.In this study, QTL mapping and genetic basis were dissected for SG related traits, such as GLAD, GLNMS etc., The results provided a genetic basis and techniques for marker-assisted selection and genetic improvement of stay-green. Meanwhile some important QTLs with stable expression and some important hot-spot chromosome regions for specific traits played critical roles to QTL functional research and clone based on mapping. |
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