Modeling Of Flag Leaf Senescence Process Of Wheat And Leaf Senescence Model Based QTL Mapping For Wheat Stay Green Traits Using A DH Population

Leaf photosynthesis is principle source of carbohydrates for wheat grain filling.Delayed leaf senescence usually leads to enhanced grain yield.The establishment of index for assessing stay green character of wheat and the identification of stable stay green germplasm and QTLs will faciliatate the wheat improvement for stay green performance.In 2011 and 2012,91 and 105 varieties or advanced lines were investagated to select a suitable model to describe the leaf senescence patterns by non-linear curve fitting method,and to establish index for stay green evaluation.In years 2012-2014,47 elite wheat varieties with diversed stay green performance were further screened for varieties with stable stay green performance.A non-stay green wheat variety Yangmai9 and a moderately stay green wheat variety Shijiazhuang8 were used as parents to produce a double haploid(DH)population by maize chromosome elimination method,The 131 DH lines were used for mapping QTL related to stay green.The results obtained were as follows:1.Three models,Logistic,Gompertz and Richards,were tested in 2011-2012 growing seasons and all can fit the leaf senescence pattern of wheat varieties having four different stay green types.The goodness of fitting of Richards model to different types of stay green varieties were similar as the Gompertz model,which is higher than the Logistic model.The goodness of fitting of Gompertz model to four stay green types were different,with a order being non-stay green group(NSG)>moderately non-stay green group(MNSG)>moderately stay green group(MSG)>stay green group(SG).2.In the two growing seasons,the development of the flag leaf senescence of four different types stay green varieties can be divided into three stages,initial senescence stage,rapid senescence stage and terminal senescence stage.Senescence rates of the three stages displayed a 'slow-fast-slow' pattern.The decrease of the percentage of green leaf area(%GLA)after anthesis was occurred mainly in the middle and late senescence stages.3.The varieties tested in the two growing seasons could be clustered into four different types,stay green(SG),moderately stay green(MSG),moderately non-stay green(MNSG)and non-stay green(NSG).The time of maximum rate of senescence(TMRS),maximum rate of senescence(MRS),green leaf area duration(GLAD)and average rate of senescence(ARS)derived from Gompertz equation showed significant difference among the four different types.The TMRS of the varieties tested in 2012 were earlier than the corresponding stay green type of varieties in 2011,while the MRS and ARS were slower in 2012 than the corresponding types in 2011.Therefore,the GLAD of the tested varieties in 2011 were longer than the corresponding types in 2012.4.Forty-seven varieties tested in years 2012-2014 also could be clustered into the above four different types.Six,eighteen,eleven and twelve varieties could be assigned as types SG,MSG,MNSG and NSG respectively based on their stay green performances in three consecutive years.5.The flag leaf senescence parameters TMRS,GLAD and ARS were significantly and positively correlated with%GLA at late filling stage,while the MRS was only significantly correlated with%GLA at late filling stage in a few varieties.In the same growing season except for MRS,the other three parameters TMRS,GLAD and ARS were significantly different among the four different types.The orders of the mean values were as following:for TMRS and GLAD,SG>MSG>MNSG>NSG;for ARS,NSG>MNSG>MSG>SG.In different growing seasons,the mean values for the flag leaf senescence parameters of the four different types were:for TMRS and GLAD,2014>2013>2012;for MRS,2013>2014>2012;and for ARS,2012>2013>2014.6.In years 2013-2014,the flag leaf senescence of Yangmai9×Shijiazhuang8 DH population under field high humidity and green-house high temperature enviromments were described by Gompertz model,and the determination coefficient of fitted equation were 0.9640-1.000.Based on the%GLA after anthesis under each environment,the DH lines were also categorized into four different types.Parameters TMRS,GLAD and ARS were significantly different among different types,but not for MRS.In the same growing season and under the same environment,GLAD,TMRS and MRS were significantly correlated.The correlation coefficient between GLAD and MRS were lower than that between GLAD and TMRS.Among different growing seasons and under different environments,the four parameters all showed relatively high variability,but their mean values all were in between the two parents.They showed normal distribution and transgressive inheritance.Except for MRS,TMRS,MRS,GLAD and ARS were significantly and positively correlated.7.A total of 232 polymorphic markers between two parents were used to genotype the DH population.The linkage map comprised of 33 linkage groups representing 19 wheat chromosomes except 4D and 5D.The linkage map has 209 loci covering a genetic distance of 1719.7 cM.The average interval between adjacent loci was 8.2cM.A total of 32 QTLs related to stay green were detected on chromosome 1A,1B,2A,2D,3A,3B,4B,5B,6D,7B and 7D under the four environments.Ten,eight,eight and six QTLs were identified for TMRS,MRS GLAD and ARS,respectively.Individual QTL accounted for 6.54%-14.95%of the phenotypic variance.Four QTL clusters were detected on chromosomes 1B,2D,3A and 4B,respectively.The QTL cluster on chromosome 3A was identified in most of environments.The QTLs for TMRS and MRS were located to different genome regions.Under water-logging and heat stress environments,the identified QTLs for stay green were different.8.The results of this study revealed that the Gompertz model were the most suitable model to describe the of leaf senescence development of wheat.The leaf senescence parameters could be applied as indicator to distinguish the difference of the stay green performance of wheat varieties.Genetic variance of stay green was widely present in current wheat varieties released from major wheat growing regions of China.QTLs controlling the onset of leaf senescence and senescence rate affecting the stay green performance were located in different chromosome regions.Genomic regions of barc45-cfa2134 on chromosome 3 A were the most important region affecting the stay green expression.