Association between Yield and Carbon Isotope Discrimination Value in Different Organs of Durum Wheat Under Drought

Carbon isotope discrimination (Δ) has been proposed as a selection criterion for transpiration efficiency and grain yield in drought‐prone environments for several C³ species, including cereals. Δ analysis, however, has mainly been concerned with grain or culm tissues and little work has been devoted to other organs. The objective of this study was to describe Δ variation in different organs and to examine the relationships between Δ and grain yield across environments. Six durum wheat genotypes with contrasted grain Δ were cultivated under rainfed conditions during three successive years at Montpellier (South of France). Δ was measured on flag leaf, stalk, awns, chaff and rachis sampled at anthesis and maturity, and on mature grain. Higher genotypic variation and closer correlation with yield were noted for grain Δ compared to other plant parts. The genotype ranking across years was more consistent for grain Δ than for other organs. Consequently, the grain seems the most effective plant part for Δ analysis in durum wheat under Mediterranean conditions. The study of Δ variation in other organs may be useful, however, to evaluate the contribution of those organs to grain filling and final yield according to environmental conditions.     

Carbon Isotope Discrimination, Leaf Ash Content and Grain Yield in Bread and Durum Wheat Grown under Full-Irrigated Conditions

Integrative physiological criteria, such as carbon isotope discrimination (Δ) and (mineral) ash content (m_a) have been found to be very useful, under drought conditions, to elucidate the association between yield gains and variation of photosynthesis‐related traits and orientate future breeding efforts. Information on this association is scarce under irrigated conditions. The relationships between Δ, m_a and yield were studied in bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. durum) under optimal (drip) irrigation in the arid conditions of north‐west Mexico. Carbon isotope discrimination was analysed on leaves at booting stage and anthesis and on grain at maturity, whereas ash content was measured on the flag leaf at anthesis and maturity. At anthesis, there were differences between bread and durum wheat during grain filling for Δ, but not for m_a. No relationship was found between grain yield and Δ. Leaf ash content at anthesis and maturity showed a broad variability within each species and were associated with grain yield. These results suggest that ash content in leaves could be also used as predictive criteria for yield not only under drought, but also under irrigated conditions, particularly when evaporative demand is high.     

Carbon Isotope Discrimination and Grain Yield Variations among Tetraploid Wheat Species Cultivated under Contrasting Precipitation Regimes

Nineteen accessions belonging to six tetraploid wheat species were evaluated and compared for carbon isotope discrimination and grain yield during two successive cropping seasons (1995 and 1996) under Mediterranean rainfed conditions. The two seasons differed markedly in precipitation regime. A wide variation for the measured traits was observed among the 19 accessions for carbon isotope discrimination and grain yield in both years. Significant differences were also noted between species accessions for Δ and grain yield. In both years, Triticum timopheevi (AG genome) showed lower Δ values than the other tetraploid species (all carrying the AB genome). Positive correlations were observed between Δ and grain yield in both years. The use of carbon isotope discrimination as an indirect selection criterion for yield under stress and the potential benefits of some alien tetraploid species in improving drought tolerance in durum wheat are discussed.     

Relationship between Carbon Isotope Discrimination, Ash Content and Grain Yield in Wheat in the Peninsular Zone of India

Carbon isotope discrimination (Δ) and ash content (m_a) have been proposed as indirect selection criteria for grain yield in wheat. The associations between Δ, m_a and grain yield were found, however, to depend highly on the environmental conditions, the organ sampled and the time of sampling. In this study, carried out in the warm conditions of the Peninsular Zone of India, the relationship between Δ, m_a and yield was studied in 30 bread and durum wheat cultivars under residual soil moisture stress (RSMS), post‐anthesis water stress (PAWS) and well‐watered (WW) conditions. Both Δ and m_a were analysed in young seedlings (four‐leaf stage), leaves at anthesis and grain at maturity. Ash content was also evaluated in leaves at booting stage and maturity. Grain Δ was lower under PAWS and RSMS than under WW, while seedling and leaf Δ did not significantly differ among water regimes. Grain yield was positively correlated to grain Δ under PAWS and negatively correlated to grain m_a under RSMS. A significant positive correlation was noted under RSMS and WW treatments between m_aL_m and grain yield. Ash content in leaf at maturity consequently appears to be a useful indirect selection criterion in environments where Δ does not show any correlation with yield. The results highlight the potential of Δ and m_a as indirect selection criteria for wheat yield in the conditions of the Peninsular Zone of India.     

Relationships between Grain Yield, Flag Leaf Morphology, Carbon Isotope Discrimination and Ash Content in Irrigated Wheat

The purpose of this study was to examine how differences in leaf angle, leaf rolling (LR) and glaucousness (GL) can modify yield components and leaf physiological traits in wheat. A set of 167 lines derived from a cross between two high‐yielding bread wheat cultivars differing for these traits was grown under flood irrigation and high evaporative demand in the north‐west of Mexico. Area, mass per unit area and chlorophyll content of the flag leaf were assessed. Carbon isotope discrimination (Δ) and ash content (m_a) were also measured. A significant correlation was found between grain yield (GY) and both Δ and m_a suggesting that, despite well‐watered conditions, leaf stomatal conductance was the main yield‐limiting factor. Leaf posture and LR did not significantly affect yield, Δ and m_a. Higher grain weight was noted, however, in lines with droopy flag leaves. Erect leaves had higher mass per unit area. GL was associated with a significant increase in GY and grain weight. Glaucous lines also had higher Δ and m_a, suggesting higher transpiration rate and lower transpiration efficiency. The study confirms that Δ and m_a represent promising criteria for GY in wheat and provides evidence that GL can contribute to higher yield, even under irrigated conditions.     

Grain Yield and Quality of Durum Wheat Landraces in a Dry Mediterranean Region of Northern Syria

Twenty-two durum wheat landraces of various origins were evaluated for performance and stability of grain yield, protein content and gluten strength (SDS sedimentation volume) at two sites of Northern Syria situated in the drought-prone part of the local durum wheat belt. Yield was recorded in three seasons, while protein content and SDS volume were assessed in two seasons only. A high “entry X environment” interaction was observed for all traits, which was significantly attributable to heterogeneity of entry regressions on the environmental mean for grain yield only. Compared to the recently-bred, widely-grown variety ‘Sham I’, some landraces showed somewhat similar yield responses, whereas others proved more stable without being significantly lower yielding. Significant variation was found for SDS volume, though only few of the best-ranking landraces for this trait also possessed an acceptable yield level. The entries did not significantly differ for protein content. The broad sense heritability estimates obtained for grain yield (0.59) and SDS volume (0.89) highlighted the interest in some of the landraces examined for improving grain yield and quality in the region.     

Evaluation of Grain Filling Rate and Duration in Bread and Durum Wheat, under Heat Stress after Anthesis

Bread and durum wheat genotypes were submitted to heat stress during the grain filling period, and relationships between grain weight and accumulated time from anthesis until maturity, using days after anthesis and growing degree days, were described by cubic polynomials. Maximum grain weight and the duration and rate of grain filling were estimated from the fitted curves. It was found that bread and durum wheat exposure to high temperatures significantly decreased grain weight and hastens physiological maturity (shortening the grain filling period). High temperatures significantly affected the rate (on a growing degree day basis) and duration (on Julian day units) of grain filling. The grain filling rate, on a thermal time basis, was positively associated with the final grain weight and the estimated maximum grain weight. The duration of grain filling does not appear to be a limiting factor for genotype grain weight stability, being mainly fixed by temperature. Grain weight of the controlled plants was positively correlated with the final and maximum grain weight of heat stressed plants. It was concluded that a high grain filling rate and a high potential grain weight are major traits that can be useful to improve heat tolerance of Triticum under Mediterranean environments.     

Carbon Isotope Discrimination and Productivity in Field-Grown Barley Genotypes

Five barley genotypes of different origins were used to examine the relationships between carbon isotope discrimination (Δ) and grain yield, yield components, dry aerial biomass and harvest index under rainfed and irrigated Mediterranean conditions. High positive correlations were found between Δ and grain yield and harvest index under both water conditions, suggesting that Δ may represent efficiency of dry matter partitioning to the grain. This hypothesis was also supported by the positive correlation found between Δ and thousand-grain weight when all the data were considered. The two drought-tolerant genotypes LM2887 and Tadmor presented the smallest difference between the two treatments for traits related to productivity as well as the highest Δ values. These results highlight the potential of Δ as a selection criterion in barley breeding in Mediterranean regions. They also encourage the study of the genetics of Δ and the identification of molecular markers linked to its variation in available progenies derived from crosses between the genotypes used in the present paper.     

Relationship between Carbon Isotope Discrimination and Grain Yield in Spring Wheat under Different Water Regimes and under Saline Conditions in the Ningxia Province (North-west China)

The relationship between grain yield and carbon isotope discrimination (Δ) was analysed in wheat grown under different water regimes in the Ningxia Province (north‐west of China). When the association was significant, the relationships between grain yield, Δ and other drought tolerance related traits, such as leaf ash content (m_a), chlorophyll concentration (Chl), relative water content (RWC), stomatal conductance (g_S) and the ratio of internal CO₂ leaf concentration to ambient CO₂ concentration (C_i/C_a), were also examined. Using correlation analysis, the relationships were determined during two consecutive years in a set of 20 spring wheat cultivars (landraces, improved varieties and advanced lines) under rainfed and irrigated conditions, including saline conditions. The relationship between Δ and yield within environments highly depended on the quantity of water stored in the soil at sowing, the quantity and distribution of rainfall during the growth cycle, and the irrigation before anthesis. Δ predicted grain yield under limited irrigation (post‐anthesis water stress) but not under pre‐anthesis water stress (rainfed conditions), fully irrigated and saline conditions. Under limited irrigation, grain Δ correlated significantly to grain yield leaf m_a at heading and maturity. It also significantly positively correlated to Chl, RWC, g_S and C_i/C_a assessed at anthesis. A precise characterization of the timing and intensity of the abiotic constraints experienced by the crop is consequently needed before implementing the use of Δ in wheat breeding programmes.     

Contribution of Different Organs to Grain Filling in Durum Wheat under Mediterranean Conditions I. Contribution of Post‐Anthesis Photosynthesis and Remobilization

Under Mediterranean conditions, drought affects cereals production principally through a limitation of grain filling. In this study, the respective role of post‐anthesis photosynthesis and carbon remobilization and the contribution of flag leaf, stem, chaff and awns to grain filling were evaluated under Mediterranean conditions in durum wheat (Triticum turgidum var. durum) cultivars. For the purpose, we examined the effects of shading and excision of different parts of the plant and compared carbon isotope discrimination (Δ) in dry matter of flag leaf, stem, chaff, awns and grain at maturity and in sap of stem, flag leaf, chaff and awns, this last measurement providing information on photosynthesis during a short period preceding sampling. Source–sink manipulations and isotopic imprints of different organs on final isotope composition of the grain confirmed the high contribution of both carbons assimilated by ears and remobilized from stems to grain filling, and the relatively low contribution of leaves to grain filling. Grain Δ was highly and significantly associated with grain yield across treatments, suggesting the utilization of this trait as an indicator of source–sink manipulations effects on grain yield. Chaff and awns Δ were better correlated with grain Δ than stem and leaf Δ, indicating that chaff were more involved in grain filling than other organs. Moreover, in chaff, sap Δ was highly significantly correlated with dry matter Δ. These results suggest the use of Δ for a rapid and non‐destructive estimation of the variation in the contribution of different organs to grain filling.     

Flag Leaf Senescence, as Evaluated by Numerical Image Analysis, and its Relationship with Yield under Drought in Durum Wheat

Senescence was evaluated at different stages of the grain‐filling period in eight durum wheat varieties using numerical image analysis (NIA). The varieties were grown under early, severe drought conditions on the high plains of Sétif in Algeria. After flowering, three different irrigation treatments were applied. Treatment effect was small, while a genotypic effect was noted for most of the senescence parameters. Senescence correlated to biomass, while the maximal rate of senescence, V_smax, correlated to thousand‐kernel weight. The potential of the method of numerical image analysis for monitoring flag leaf senescence, detecting genotypic variability and selecting genotypes with delayed senescence is discussed.     

Effect of Shading on the Growth and Yield of Mungbean (Vigna radiata [L.] Wilczek)

Mungbean grown as intercrop suffers shading stress form companion crop at different growth stages. Grain filling stage, which appears to be very much sensitive to light conditions, needs special attention to deal with, in order to maximize the benefit from intercropping systems. Growth and yield response of mungbean to different shading conditions imposed at the onset of pod formation stage was evaluated. Shading nets were used to cut down the incident photosynthetic active rediation by 15 %, 45 % and 75 %. There was almost no difference between the control and 15 % shaded plants for all the parameters studied. Total dry weight was found to decrease with increase in shading intensity and this phenomenon continued till the maturity of the crop. The crop growth rate, relative growth rate and net assimilation rate decreased due to shading. Lower specific leaf weight and higher chlorophyll content were due to increased shading. Decreased photosynthetic active radiation caused significant reduction in pods per plant and thus there was a significant decrease in seed yield per plant. In order to avoid yield loss due to shading at grain filling stage, agronomic manipulation and selection of suitable genotypes are necessary.     

Relationship between Carbon Isotope Discrimination and Mineral Content in Wheat Grown under Three Different Water Regimes

Carbon isotope discrimination (Δ) has been proposed as an indirect selection criterion for transpiration efficiency and grain yield in wheat. However, because of the high cost for Δ analysis, attempts have been carried out to identify alternative screening criteria. Ash content (m_a) has been proposed as an alternative criterion for Δ in wheat and barley. A pot experiment was conducted to analyse the relationship between Δ and m_a in flag leaf and grain. Plants of 10 genotypes were cultivated under three different water regimes corresponding to moderate, intermediate and severe drought stress obtained by maintaining soil humidity at 75 %, 55 % and 45 % of the humidity at field capacity, respectively. Δ and m_a in flag leaf and grain showed significant differences between the moderate, intermediate and severe drought stress levels. Significant correlations were found among genotypes for Δ and m_a in flag leaf under severe drought stress, and for Δ and m_a in grain under intermediate and moderate drought stress. In flag leaf at anthesis, Δ was negatively associated to K content and positively to Mg content. At maturity, Δ in grain was negatively correlated with Mg and Ca contents in flag leaf and grain, respectively. These results suggested that these traits may be potentially useful traits, which could be surrogates for Δ.     

大豆和小麦不同基因型的碳同位素分馏作用及水分利用效率

26个大豆基因型和18个小麦基因型的叶片和种子的稳定碳同位素分馏值(△13C)在正常供水和缺水的田间条件下皆有明显的基因型差别。土壤干旱降低△13C值，提高水分利用效率(WUE)并增大了不同基因型间的差值。抗旱性不同的基因型的叶片和种子的△13C平均值及相应的WUE与抗旱性大小之间表现一定的规律性变化，抗旱性强的基因型的     

Impact of Management Practices on Grain Yield and Grain Protein Relationships in Durum Wheat

We examined the relationship between grain yield (GY) and grain protein concentration (GPC) in durum wheat ( Trticum turgidum L. var. durum ) as affected by N application rate, seeding rate, and irrigation levels. Field experiments were conducted for four years with five N rates, five seeding rates, and four Irrigation regimes: A. Only a preplant irrigation; B. A + one irrigation at tillering; C. B + one irrigation at booting stage; and D. C + one irrigation at early soft dough stage. These treatments produced a large variation in GY and GPC which provided the basis for examining the GY-GPC relationship by all possible correlation analyses and by analysis of variance after partitioning the bivariate responses (GY and GPC) into pairs of univariate responses. The contribution of N, seeding rate, and irrigation on parallel (simultaneous changes in the same direction) and opposite changes in GY and GPC was determined. The effects of N and seeding rate on parallel increase in GY and GPC were significant. For a given level of irrigation, increasing N application resulted in significant parallel increase in GY and GPC to the highest level of N. At low N levels, increase in irrigation level from A to B increased GY and decreased GPC; however, it was not true at higher N levels. For a given N level, GY plateaued at irrigation C, whereas GPC increased up to irrigation D. The overall effects of irrigation treatments on parallel changes (positive correlation) in GY and GPC significantly outweighed their effects on opposite changes (negative correlation) in GY and GPC. Increasing levels of N and irrigation improved the correlation between GY and GPC and the yield-protein index. This study suggests that with proper management practice it is possible to increase both GY and GPC simultaneously and obtain high protein yield ha⁻¹.     

The Physiology and Stability of Leaf Carbon Isotope Discrimination as a Measure of Water‐Use Efficiency in Barley on the Canadian Prairies

Temporal and seasonal water deficit is one of the major factors limiting crop yield on the Canadian prairie. Selection for low carbon isotope discrimination (Δ¹³C) or high water‐use efficiency (WUE) can lead to improved yield in some environments. To understand better the physiology and WUE of barley under drought conditions on the Canadian prairie, 12 barley (Hordeum vulgare L.) genotypes with contrasting levels of leaf Δ¹³C were investigated for performance stability across locations and years in Alberta, Canada. Four of those genotypes (‘CDC Cowboy’, ‘Niobe’, ‘170011’ and ‘Kasota’) were also grown in the greenhouse under well‐watered and water‐deficit conditions to examine genotypic variations in leaf Δ¹³C, WUE, gas exchange parameters and specific leaf area (SLA). The water‐deficit treatment was imposed at the jointing stage for 10 days followed by re‐watering to pre‐deficit level. Genotypic ranking in leaf Δ¹³C was highly consistent, with ‘170011’, ‘CDC Cowboy’ and ‘W89001002003’ being the lowest and ‘Kasota’‘160049’ and ‘H93174006’ being the highest leaf Δ¹³C. Under field and greenhouse (well‐watered) conditions, leaf Δ¹³C was significantly correlated with stomatal conductance (g_s). Water deficit significantly increased WUE, with ‘CDC Cowboy’– a low leaf Δ¹³C genotype with significantly higher WUE and lower percentage decline in assimilation rate (A) and g_s than the other three genotypes (‘Niobe’, ‘170011’ and ‘Kasota’). We conclude that leaf Δ¹³C is a stable trait in the genotypes evaluated. Low leaf Δ¹³C of ‘CDC Cowboy’ was achieved by maintaining a high A and a low g_s, with comparable biomass and grain yield to genotypes showing a high g_s under field conditions; hence, selection for a low leaf Δ¹³C genotype such as ‘CDC Cowboy’ maybe important for maintaining productivity and yield stability under water‐limited conditions on the Canadian prairie.     

不同播期对冬小麦粒重形成及产量的影响

以4个冬小麦品种为材料,研究了不同播期条件下籽粒灌浆特征参数、粒重和产量的差异。结果表明:播期对千粒重的影响存在差异,洛旱6号、洛麦21号和豫麦49不同播期之间的籽粒千粒重存在显著差异,但播期对偃展4110的千粒重影响不大。在不同播期下,灌浆过程中平均灌浆速率、快增期灌浆速率对粒重的影响较大。播期对不同品种灌浆高峰出现的日期影响基本一致,早播期>晚播期>中播期.但较早播种时,洛旱6号、洛麦21号和豫麦49灌浆高峰出现较早,灌浆速率大,晚播时偃展4110灌浆高峰出现较早,灌浆速率大。播期对4个品种产量的影响均以中播最高,在河南旱区生态条件下,似偃展4110的春性品种适宜播期为10月中下旬,洛旱6号、洛麦21号等似豫麦49的半冬性品种适宜播期为10月中旬。     

小麦穗内芒长与粒重关系的粒位效应

为了探索有芒小麦穗内芒长与粒重的关系,本试验选取两个小麦品种‘煤生0308’和‘煤生5号’,对其不同粒位的芒长和粒重进行了研究。结果表明,芒长与粒重呈显著正相关,相关系数分别为0.373（P=0.0046）和0.267（P=0.0256）。然而,在相同粒位不同小穗位,芒长与粒重的相关程度是不同的。在第一粒位,芒长和粒重相关性不显著;在第二粒位,芒长和粒重呈显著正相关,相关系数分别为0.3814（P=0.0454）和0.4802（P=0.0170）;在第三粒位,芒长和粒重呈极显著正相关,相关系数分别为0.8455（P=0.0003）和0.8516（P=0.0001）。     

源库改变对小麦籽粒蛋白质,淀粉含量及产量的影响

利用蛋白质含量及产量各不相同3个春小麦品种．研究了源库改变对淀粉、蛋白质沉术；及单侏产量的影响．结果表明：源库改变明显地影响着籽粒蛋白质的含量，而对淀粉、可溶性糖含量影响不大；品种间蛋白质含量对源库变化的反应不同；千粒重的增减也因品种而异；淀粉的沉积主要受库的限制，而源库都影响着蛋白含量；旗叶在产量和蛋白形成中起着同样重要作用。     

Evaluating Leaf Ash Content and Potassium Concentration as Surrogates of Carbon Isotope Discrimination in Grassland Species

Leaf ash content and potassium (K) concentration were evaluated as surrogates of carbon isotope discrimination (Δ) of the dominant species in an upland grassland in a 3-year experiment. Previous results reported positive correlations between Δ and ash content or mineral concentrations, attributing this relationship to the passive accumulation, through the transpiration stream, of minerals in the vegetative plant parts. We found only a weak positive correlation between Δ and ash content or K concentration in 1997 (r=0.79, P < 0.05 and r=0.77, P < 0.05, respectively). No significant correlation was found between the traits in 1998 and 1999. When four of the seven most abundant species ( Poa pratensis , Lolium perenne , Festuca valida and Taraxacum officinale ) were grown under different treatments (mixed sward, monoculture, and nitrogen and P additions in mixed sward), a curvilinear relationship between Δ and ash content or K concentration was evident. Thus, our findings suggest that leaf ash content and K concentration cannot serve as surrogates of carbon isotope discrimination (Δ). Small genotype × environment interactions were reported for the three traits measured; the interactions were smallest for ash content. A positive correlation between leaf ash content and soil water content (at 5 and 15 cm depth) was found for four species ( P. pratensis , L. perenne , F. valida and Achillea millefolium ) and for the community as a whole. No significant correlation was found between leaf K concentration and soil water content.