Research On Drought-resistance And Water-saving Characteristics Of Spring Wheat In Northwestern U.S.

Utilizing the drought-resistance and water-saving characteristics of crop, and enhancingresource use efficiency in crop production, is not only an important method for boosting cropproduction efficiency, but also a crucial aspect in water-saving agricultural field. Tounderstand the drought-resistance and water-saving characteristics of spring wheat genotypesin northwestern U.S., and reveal the agronomic and physiological basics of them, a two-yearfield experiment with30spring wheat genotypes and three irrigation regimes was carried outin2009and2010field seasons. Experiment was laid out in a split block design, with threereplicates, keeping irrigation regimes in main plots and genotypes in subplots. Three irrigationregimes were: well-watered, moderate drought stress, and severe drought stress. Yield,agronomic traits, physiological traits, water use efficiency (WUE), and nitrogen use efficiency(NUE) were evaluated. The objectives of this study were to:(i) establish the relationshipsbetween agronomic traits, physiological traits, and grain yield (GY) responses to drought;(ii)evaluate WUE and NUE in wheat genotypes and determine the relationships between themand yield under different water conditions;(iii) characterize and prioritize the30wheatgenotypes for yield, drought-resistance, and water-saving characteristics; and analyse theagronomic and physiological basics of the characteristics;(iv) propose effective indices forevaluating yield, drought-resistance, and WUE in spring wheat genotypes; and (v) provide thetheoretical basis for achieving more efficiently water use in crop production. Preliminaryresults from this study are as follows:1, Significantly different responses to drought stress were observed in grain yield (GY)among different spring wheat genotypes. In the30genotypes, IDO599, Alturas, and IDO702produced high GY across different water conditions, which were called high-yield genotype(HYG); Klasic, Choteau, UC1600, Snowcrest, and Cataldo produced less GY than othergenotypes under all irrigation regimes, which were called low-yield genotype (LYG);compared with other genotypes, Agawam, McNeal, and Alpowa produced greater GY undersevere drought stress, but less GY under the well-watered regime, which were calleddrought-resistant genotype (DRG); IDO686and Lolo produced greater GY under thewell-watered regime but less GY under severe drought stress, which were called drought-susceptible genotypes (DSG). Selecting suitable genotypes for different waterenvironments may be crucial for improving yield productivity, for example, HYG and DRGcan be planted in water deficit environments, and HYG and DSG can be planted in moistenvironments.2, Drought stress caused noticeable fewer days to physiological maturity (PMD), shorterplant height (HT) and exposed peduncle length (EPL), smaller grain volume weight (GVW),kernel weight (KW) and kernel diameter (KD), and higher grain protein content (GPC). Alltarget traits were significantly correlated with GY except for days to heading (HD) in2010.Stepwise regression indicated that PMD, HT, and GVW (2009)/GPC (2010) togetherexplained82%and93%of the total phenotypic variation of GY. The optimum materials formeasuring coleoptile length (CL) are8-day old and7-day old seedling, respectively for thecultivation temperatures of15℃and20℃. For the seedling traits, CL and number of roots(RN) had high heritability, while longest root length (LRL) and total root length (TRL) hadlow to intermediate heritability. The relationships between CL, RN, and root length (RL) werenot significant, indicating that these traits are relatively independent. CL was not correlatedwith HT, while EPL was positively correlated with HT.3, Drought stress accelerated flag leaf senescence (FLS), decreased flag leaf carbonisotope discrimination (CID) and grain CID, increased canopy temperature (CT), acceleratedflag leaf chlorophyll breakdown, and reduced flag leaf relative water content (RWC). Flagleaf CID, grain CID, and flag leaf RWC were positively correlated with GY, whereas FLSand CT were negatively correlated with GY. Principal components analysis indicated thatFLS, leaf CID, and CT together explained92%of the total phenotypic variation of GY. Theoptimal stage for evaluating FLS and CT is Feekes11.2(kernels mealy ripe). For predictinggrain yield, FLS evaluated at Feekes11.2would be more reliable under drought stress whileCID would be more reliable under severe drought stress. CT evaluated at both anthesis andgrain filling could help predict yield, but CT at anthesis would be more reliable for droughtstress conditions while CT at grain filling would be more reliable for well-watered conditions.The optimal stage for evaluating flag leaf chlorophyll content index (CCI) is Feekes11.1(kernels milky ripe). CCI was not correlated with GY, but CCI decrease (CCID) wasnegatively correlated with GY. CCID could be used as an index to predict grain yield, and theCCI value may be considered as an indicator for screening drought resistant genotypes inwheat breeding programs.4, Irrigation decreased the WUE (assessed by flag leaf δ13C) and NUE (assessed by flagleaf C/N ratio) of all30genotypes, but the decrease of WUE and NUE differed significantly among the four groups (HYG, LYG, DRG, and DSG). The relationship between WUE andNUE was positive and significant under severe drought stress, but non-significant underwell-watered. This infers that the selection of high WUE may benefit high NUE selectiononly under the drought conditions, and vice versa. In spring wheat, high WUE and low NUEshould be selected in the well-watered environments while low WUE and high NUE shouldbe selected under the drought conditions. WUE and NUE were both negatively correlatedwith GY, but a few superior genotypes which possessed better yield and resource useefficiency (WUE and NUE) were identified from the30spring wheat genotypes. Therefore,screening WUE and NUE in HYG and DRG groups may be a feasible way to ameliorateresource use efficiency without yield penalties.5, This study put forward new evaluation indices [high yield index (HYI), droughtresistance index (DRI), water use efficiency index (WUEI), and comprehensive index (CI)]and their calculation methods, and the grouping criteria in spring wheat genotypes. Based onHYI, spring wheat genotypes can be divided into three groups: high yield, medium yield, andlow yield. Based on DRI, spring wheat genotypes can be divided into three groups: strongdrought resistant, drought resistant, and drought susceptible. Based on WUEI, spring wheatgenotypes can be divided into three groups: high WUE, medium WUE, and low WUE. Theevaluation indices which can evaluate high-yielding, drought resistance, and water-savingseparately, would promote the screening and utilizing of superior wheat genotypes.