Increased climatic variability and more frequent episodes of extreme conditions may result in crops being exposed to more than one extreme temperature event in a single growing season and could decrease crop yields to the same extent as changes in mean temperature. The developmental stage of the crop exposed to increased temperatures will determine the severity of possible damage experienced by the plant. It is not known whether or not the damaging effects of heat episodes occurring at different phenological stages are additive. In the present study, the interaction of high‐temperature events applied at the stages of double ridges and anthesis in Triticum aestivum (L.) cv. Chablis was investigated. Biomass accumulation of control plants and that of plants experiencing high temperatures during the double‐ridge stage were similar and were reduced by 40 % when plants were subjected to a heat event at anthesis. Grain number on the main and side tillers declined by 41 %, and individual grain weight declined by 45 % with heat stress applied at the double‐ridge stage and anthesis or at anthesis alone. The harvest index was reduced from 0.53 to 0.33. Nitrogen contents in leaves were reduced by 10 % at the double‐ridge stage and by 25 % at anthesis. The maximum rates of CO2 assimilation increased with heat stress at the double‐ridge stage and higher rates were maintained throughout the growing season. The results clearly indicate that an extreme heat event at the double‐ridge stage does not affect subsequent growth or the response of wheat to heat stress at anthesis.

Waterlogging is a widespread limiting factor for wheat production throughout the world. To identify quantitative trait loci (QTLs) associated with waterlogging tolerance at early stages of growth, survival rate (SR), germination rate index (GRI), leaf chlorophyll content index (CCI), root length index (RLI), plant height index (PHI), root dry weight index (RDWI), shoot dry weight index (SDWI), and total dry weight index (DWI) were assessed using the International Triticeae Mapping Initiative (ITMI) population W7984/Opata85. Significant and positive correlations were detected for all traits in this population except RLI. A total of 32 QTLs were associated with waterlogging tolerance on all chromosomes except 3A, 3D, 4B, 5A, 5D, 6A, and 6D. Some of the QTLs explained large proportions of the phenotypic variance. One of these is the QTL for GRI on 7A, which explained 23.92% of the phenotypic variation. Of them, 22 alleles from the synthetic hexaploid wheat W7984 contributed positively. These results suggested that synthetic hexaploid wheat W7984 is an important genetic resource for waterlogging tolerance in wheat. These alleles conferring waterlogging tolerance at early stages of growth in wheat could be utilized in wheat breeding for improving waterlogging tolerance.

为探讨拔节期渍害对小麦籽粒品质性状的影响,以34份小麦品种(系)为材料,比较了渍水处理和对照组的籽粒特性、面团流变学性状及溶剂保持力(SRC)的变化。结果表明,品种对所调查籽粒的品质性状、面团流变学特性及SRC均有显著或极显著影响,渍水处理对千粒重、峰值面积和峰值时间以及SRC有显著影响。渍水后,籽粒性状中的千粒重和硬度、面团流变学特性中的峰值面积和峰值时间分别较对照下降9.09%、3.76%、6.86%、7.49%,蔗糖SRC值和乳酸SRC值分别较对照降低2.68和4.39个百分点,差异达极显著水平。根据渍水前后的品质变化及相关性分析,上述性状中的千粒重、蔗糖SRC值和乳酸SRC值可以作为小麦品质耐渍性筛选指标。根据K-Means法统计供试小麦品种(系)耐渍性对品质影响的差异,发现宁麦9号、扬16-157、皖西麦7号和鄂麦6046品质耐渍性较好,可作为培育耐渍品种的亲本加以利用。本研究结果为小麦耐渍育种及渍害对小麦生长发育的影响提供了理论依据。

\nThe growth reduction of wheat (Triticum aestivum L.)\nduring and after waterlogging stress depends on the depth of water from the\nsoil surface. In a pot experiment with 3-week-old plants, soil was waterlogged\nfor 14 d at the surface, or at 100 or 200 mm below the surface, and pots were\nthen drained to assess recovery. A fully drained treatment kept at field\ncapacity served as control. During waterlogging, the relative growth rate of\nroots decreased more than that of shoots (by 6–27% for shoots, by\n15–74% for roots), and plant growth was reduced proportionally as\nthe water level was increased. Light-saturated net photosynthesis was reduced\nby 70–80% for the two most severe waterlogging treatments, but\nwas little affected for plants in soil waterlogged at 200 mm below the\nsurface. The number of adventitious roots formed per stem in plants grown in\nwaterlogged soil increased up to 1.5 times, but the number of tillers per\nplant was reduced by 24–62%. The adventitious roots only\npenetrated 85–116 mm below the water level in all waterlogging\ntreatments. Adventitious root porosity was enhanced up to 10-fold for plants\ngrown in waterlogged soil, depending on water level and position along the\nroots. Porosity also increased in basal zones of roots above the water level\nwhen the younger tissues had penetrated the waterlogged zone. Fourteen days\nafter draining the pots, growth rates of plants where the soil had been\nwaterlogged at 200 mm below the surface had recovered, while those of plants\nin the more severely waterlogged treatments had only partially recovered.\nThese findings show that the depth of waterlogging has a large impact on the\nresponse of wheat both during and after a waterlogging event so that\nassessment of recovery is essential in evaluating waterlogging tolerance in\ncrops.\n

Drought is the most severe abiotic stress reducing rice yield in rainfed drought prone ecosystems. Variation in intensity and severity of drought from season to season and place to place requires cultivation of rice varieties with different level of drought tolerance in different areas. Multi environment evaluation of breeding lines helps breeder to identify appropriate genotypes for areas prone to similar level of drought stress. From a set of 129 advanced rice (Oryza sativa L.) breeding lines evaluated under rainfed drought-prone situations at three locations in eastern India from 2005 to 2007, a subset of 39 genotypes that were tested for two or more years was selected to develop a drought yield index (DYI) and mean yield index (MYI) based on yield under irrigated, moderate and severe reproductive-stage drought stress to help breeders select appropriate genotypes for different environments.

The question of choice of selection criterion when lines are grown in stress and non‐stress environments is examined from a theoretical standpoint in this paper. Tolerance to stress is defined as the difference in yield between stress and non‐stress environments, while mean productivity is the average yield in stress and non‐stress environments. Equations are developed for the genetic correlations of tolerance and mean productivity with one another and with yields in stress and non‐stress environments in terms of the ratio of genetic variances and the genetic correlations between yields in stress and non‐stress environments. These equations show that selection for tolerance to stress will generally result in a reduced mean yield in non‐stress environments and a decrease in mean productivity. Selection for mean productivity will generally increase mean yields in both stress and non‐stress environments. Tolerance and mean productivity show negative genetic correlations whent he genetic variance in stress environmentsi s less than the genetic variance in non‐stress environments. This result provides an explanation for the positive correlations often reported between regression coefficient stability and mean productivity; a line with high tolerance to stress normally would have a low regression coefficient stability and genetic variances in stress environments are generally lower than in non‐stress enviornments.

乙烯响应因子在植物非生物胁迫应答中起重要作用。为了解TaERF2在小麦湿害胁迫下作用的分子机理,本研究对TaERF2基因及其编码蛋白序列特征进行分析,并检测TaERF2在不同耐湿品种中的表达特征及原核表达。结果表明,TaERF2基因含有2个外显子和1个内含子,编码355个氨基酸序列,具有典型的AP2/ERF保守结构域和YRG、RAYD基序。AP2/ERF家族转录因子进化和同源比对分析表明,TaERF2属于AP2/ERF家族B2组,与拟南芥AtRAP2.12、AtHRE1和水稻OsSNORKEL1、OsSNORKEL2有较高的同源性,且启动子区域含有缺氧厌氧顺式元件,推测TaERF2可能为湿害胁迫响应基因。湿害胁迫后,TaERF2在小麦根系中特异表达,在耐湿小麦品种宁麦9号根系中的表达显著上调,2~4 h表达量达到最高,然后显著降低,而在不耐湿小麦品种郑麦1354根系中的表达无显著上调。原核表达结果显示,TaERF2可以快速响应ZPTG刺激诱导,与上述宁麦9号根系中的表达模式相似,表明TaERF2在小麦耐湿中具有重要调节作用。本研究为解析小麦耐湿分子调控机制提供了理论参考。

With a view to understanding the basis of cultivar differences in yield under drought, a wide range of cereal cultivars representing durum wheats (Triticum turgidum L.), triticales (X Tritosecale Wittmack), barleys (Hordeum vulgare), and especially tall and dwarf bread wheats (T. aestivum L.) were studied in field experiments in north-western Mexico over three seasons. Drought was created in this rain-free environment by permanently terminating irrigation at various stages before anthesis. Control treatments were well watered throughout the growing period. Detailed measurements of plant water status, leaf area and dry matter production, anthesis date, yield components and grain yield were made. This paper presents primarily the grain yield data. Drought levels were such that the mean yield of all cultivars under drought ranged from 37 to 86% of control yield, corresponding to irrigation cut-offs varying from 69 days before mean anthesis date to only 10 days before. In each experiment the grain yield under drought showed highly significant cultivar differences, which appeared consistent between years. Yields were adjusted for drought escape by using a correction factor which ranged from 2.9 to 8.5 g/m2 per day advance in flowering, being greater in experiments with less severe drought. The demonstration of linear relationships between cultivar yield and drought intensity, as indicated by the mean yield of some or all cultivars, prompted the consideration of cultivar yield under drought as the function of yield potential (Yp, yield without drought), drought susceptibility index (S), and intensity of drought. The cultivar groups showing lowest S values (most droughtresistant) were tall bread wheats and barleys; dwarf bread wheats were intermediate, and durum wheats and triticales were the most susceptible. However, because dwarf wheats have a higher yield potential (Yp) than tall bread wheats, it is suggested that, as a group, tall bread wheats would outyield dwarf wheats only under very severe drought. Also there was considerable within-group variability of S and Yp. Cultivar S values were consistent across experiments. Yield responses of tall and dwarf bread wheat groups obtained in these experiments agreed with those seen in extensive international trials under dryland conditions.