| High temperature stress is a major problem in most of the wheat growing areas.Developing heat tolerant cultivars has become a principal breeding goal in China and worldwide.Traits and molecular markers associated with high temperature tolerance can be used to develop heat tolerant cultivars in wheat.The present study was conducted to identify chromosomal regions associated with grain weight and its related traits,seedling growth,root traits,and SPAD chlorophyll content（SCC）,which are indicative of high temperature tolerance.The main results obtained are as fellows:1.A winter bread wheat double haploid（DH）population resulting from the Nongda 3338/Jingdong 6 cross was grown across a wide range of environments where heat stress are experienced naturally or artificially with spring-sowing environments in comparison to winter-sowing environments.A molecular genetic linkage map including 10149 SNP and SSR marker loci was used for QTL analysis of thousand grain weight（TGW）,grain length（GL）,grain width（GW）,grain length-width ratio（LWR）,grain area（GA）and grain perimeter.A total of 234 QTLs for 6 traits in 11 environments were identified,that included 53 QTLs for TGW,29 QTLs for GL,36 QTLs for GW,32 QTLs for LWR,41 QTLs for GA and 43 QTLs for grain perimeter.Chromosomal regions with QTLs detected consistently for multiple environments were identified for each trait,Of them,4 stable QTLs for TGW were detected in at least four of the 11 environments,among which QTgw-4A.1 QTgw-4B.3.QTgw-4B.6 and QTgw-4B.10,explained 3.81-7.69,12.24-28.7,4.32-21.99 and 19.91-38.14%of phenotypic variation,respectively.Five QTLs for TGW were specifically expressed under spring-sowing environments.Pleiotropic QTLs were found on chromosomes 1B,2A,4A,4B,4D,5A,6A and 7A.The identified genomic regions controlling wheat grain weight and its related traits can be targeted during further studies for their genetic dissection.2.In the same population,seedling growth trait was examined in terms of shoot length,shoot fresh and dry weight during early vegetative stages under controlled and heat stress condition.Total 23 QTLs were detected for seedling growth parameters.These QTLs were distributed on chromosome 2A,2B,3B,4B,4D,6A,7A,7B and 7D.Four common major QTLs were detected for shoot length both under controlled and heat stress condition on chromosome 4B and 4D.There is also a common QTL mapped for shoot fresh weight under both growing condition on 4B.One stable QTL was detected for shoot fresh and dry weight under heat stress condition on chromosome 7A.As an indicator of heat tolerance,HSI was calculated for individual DH line.QTL analysis was performed to map QTLs related to seedling growth traits and their HSI.Seven QTLs were mapped on chromosome 2A,2B,3B and 7D for HSI of seedling growth traits.Among them,one stable QTL for HSI of shoot fresh weight was mapped on chromosome 7D which is consistently detected for HSI of shoot dry weight.Single QTL was mapped on 3B for shoot dry weight under heat and HSI of the same trait.3.Root morphological parameters were measured in seedling stage using hydroponic culture technique.Total root length,root surface area,root volume,number of root tips and main root length were measured DH population.Total 39 QTLs distributed on chromosomes 2A,2B,3A,4B,4D,5A,6A,6D,and 7B were identified for root traits.Eight important QTL clustered were identified on chromosome 2A,3A,4D and 5A.Important QTL rich regions on chromosome 2A（wsnpExc1951628480622-Xgwm614b）,3A（Excaliburc24354 465-Kukrirepc102151697 and Xwmc695-IAAV5821）and 4D（RAC875c5827554-wsnpBF473052DTa21）were found as they had pleiotropic effect for controlling root traits.Negative correlation was found between root traits and plant height.Root traits was found unaffected by Rht2 gene on chromosome 4D.4.A population of 271 recombinant inbred lines（RIL）developed from a cross between BN 6 and YD 1817 was used to map QTLs for chlorophyll content in flag leaves at 6 days after pollination.Composite interval mapping identified two QTL regions significantly associated with SPAD values on chromosomes 3A.The variability explained by these QTLs were 5.72%and 5,42%,respectively.5.The substitution lines of two nuclear genomes and ten alien cytoplasm were examined to identify the effect of cytoplasm,and cytoplasmic-nuclear genome interaction on traits associated with heat tolerance.Thousand grain weight（TGW）,membrane thermal stability（MTS）and chlorophyll a fluorescence were used as tools for screening of heat tolerance.Significant variability was observed between nuclear,cytoplasm,and nuclear-cytoplasmic combinations.Two of the cytoplasms provided improved tolerance to heat with two nuclear parent for at least two traits.The role of cytoplasm may be considered in wheat breeding programs as they breed for high temperature tolerance,but the nature of interaction between cytoplasm and nuclear gene content needs to be better understood. |
