Evaluation Of Traits Related To Carbon Isotope Discrimination In Bread Wheat For Drought Adaptation And Identification Of SNPs In Its Candidate Gene TaER

Drought is a major issue affecting crop grain yield. Augmenting grain yield and crop wateruse efficiency （WUE） under drought is crucial for enhancing world crop production and foodavailability. Relationships of carbon isotope discrimination （Δ） with gas exchange parameters,yield traits, ash contents, mineral concentrations, and leaf chlorophyll content （Chl） wereexamined on a collection of49-wheat （Triticum aestivum L.） genotypes under two levels ofrestricted irrigation （W120and W200）. Drought tolerance indices were also calculated and analysedto screen wheat genotypes for their drought tolerance. The trial was carried out under controlledirrigation in a rainout shelter. Water stress was applied at grain filling stage. The severe waterdeficit regime received40%less water than the moderate water deficit regime. The SNPs in thecandidate gene TaER were also investigated by sequencing and their correlations with those traitswere also estimated. The main results were as following.Analysis on the correlations between CID and the traits revealed that significant and positivecorrelations were found between Δ and photosynthesis rate （A）, stomatal conductance （gs）,transpiration rate （E）, and the ratio of intercellular CO₂concentration to ambient CO₂concentration （Ci/Ca）, while significant and negative correlations were obtained between Δ andintrinsic water use efficiency （iWUE） under both water regimes. Strong positive correlations of Δwith grain yield （GY）, biomass （BM） and harvest index （HI） were also observed in both waterregimes. Mean values of all other parameters were calculated for the five genotypes based on Δvalue, i.e. which produced the highest Δ and which produced the lowest Δ. It was found thatmean values for all the parameters in the high Δ genotypes were higher that for low Δ genotypesexcept for iWUE in both water regimes. These results suggest that Δ may be a good trait as anindirect selection criterion for genotypic improvement in drought tolerance of wheat underrestricted irrigation, especially in conditions similar to those encountered here where limitedwater was applied during grain filling.Carbon isotope discrimination （Δ） has been recognized as a valuable phenotyping tool in breeding wheat for drought adaptation and yield potential. The associations of ash content,concentrations of individual mineral （Ca, K, Mg, Fe and Mn） with grain Δ and grain yield wereinvestigated to assess the possibility for these traits as an alternative or reciprocal criterion tograin Δ in evaluating yield potential and drought tolerance in wheat. The results revealedsignificant （P <0.01） and negative correlations between ash content （AC） and potassiumconcentration （K） with grain Δ, and between AC and grain yield under both water regimes, whilemanganese concentration （Mn） was negatively correlated with grain Δ under W120regime andmagnesium concentration （Mg） correlated negatively under the W200regime. These resultsconfirmed that ash content and K concentration in grain could be a potentially useful andeconomical alternative criterion to grain Δ in the evaluation of differences in yield potential anddrought resistance in wheat under drought conditions.Drought tolerance indices （MP, GMP, STI, SSI, TOL, YI and YSI） based on the grain yieldunder water-stressed （Ys） and well-watered （Yp） environments were also calculated for thescreening of these genotypes for drought adaptation. The mean values for all the traits decreasedunder water-stressed treatment. Biological yield （BM） and grain yield （GY） were the mostsensitive traits to water stress which reduced by more than25%, while stomata characteristics andspike length were the least affected traits with a decrease of less than10%. Grain yield undersevere-stressed （Ys） and moderate-stressed （Yp） environments were positively and significantlycorrelated with the indices MP, GMP, and STI. So, these indices were considered as a betterpredictor of potential yield Ys and Yp than TOL, SSI and YSI. Principal component analysisclassified the genotypes into three groups. First group contained genotypes with high droughtsusceptibility and only suitable for non-stressed environments. Second group consisted ofdrought tolerant genotypes suitable for stressed environments. Third group included genotypeswith low yielding performance. Cluster analysis classified the genotypes into two groups i.e.,drought resistant with moderate to high yield stability group and drought susceptible with highyield performance group. MP, GMP and STI were found effective in screening genotypes withdifferent levels of drought tolerance. Therefore, these indices could successfully be used as aselection criterion for the screening of genotypes in breeding programs.Candidate gene based association study which involves the identification of causative singlenucleotide polymorphism （SNP） for excellent traits has been proposed as a promising approachto dissect complex traits in plants. The genetic association was identified between SNPs from1.1Kb partial sequence of wheat ERECTA genes （TaER-1and TaER-2from D-genome and B- genome of wheat, respectively） with different morpho-physiological traits （Carbon isotopediscrimination, photosynthesis rate, stomatal conductance, transpiration rate, intrinsic water useefficiency, plant height, leaf length, leaf width, stomatal density, epidermal cell density andstomatal index） in wheat genotypes. Thirty nine SNPs were identified in the coding regions of1105bp sequence of TaER-1gene in33genotypes, of which twenty four SNPs causednonsynonymous mutations and fifteen SNPs caused synonymous mutations. Whereas thirty oneSNPs were located in the coding regions of1108bp sequence of TaER-2gene in26genotypes,of which eighteen SNPs caused nonsynonymous mutations and thirteen SNPs causedsynonymous mutations. In addition, thirty five SNPs in TaER-1and nine SNPs in TaER-2werealso identified in the non-coding regions. The genetic association study revealed that SNPs inboth genes do associated with different morph-physiological properties.