Mapping loci associated with milling yield in wheat (Triticum aestivum L.)

A partial genetic linkage map constructed using 150 single seed descent (SSD) lines generated from a cross between the hexaploid wheat varieties Schomburgk and Yarralinka was used to identify loci controlling milling yield. Milling yield data were obtained using seed collected from field trials conducted at different sites over two seasons. The estimated broad-sense heritability of milling yield in this population was calculated as 0.48. In the preliminary analysis, two regions were identified on chromosomes 3A and 7D, which were significantly associated with milling yield and accounted for 22% and 19% of the genetic variation, respectively. Bulked segregant analysis in combination with AFLP identified other markers linked to these loci, as well as an additional region on chromosome 5A, which accounted for 19% of the genetic variation. The applicability of these markers as selection tools for breeding purposes is discussed.     

Effects of foliar applied benzyladenine on grain yield and grain protein in wheat (Triticum aestivum L.)

The effects of foliar applications of nitrogen and benzyladenine (BA) on grain yield and grain protein of wheat grown under field conditions were studied over 2 years with 5 cultivars at 2 locations. Nitrogen (N) at 20 kg.ha^–1, and BA at 100 or 800 mg.l^–1 were applied alone or combined at pre and post-anthesis; applications of BA at 8 mg.l^–1 were also made on individual ears in order to study the effect on cell number. Weekly determinations of the chlorophyll content of the flag leaf were conducted after anthesis to study leaf senescence. At harvest, yield, yield components and grain protein percentage were determined. N and BA applications delayed chlorophyll loss in the flag leaf, but modified neither yield nor yield components. Foliarly applied BA increased grain protein in four of the five cultivars tested. It is concluded that delay of the senescence induced by BA might allow more energy to be available for N uptake by the crop leading to an increase in grain protein.Research supported by a CAFPTA grant 1656/86 and by CONICET, PID 30017700/85.CONICETComisión de Investigaciones Cientificas de la Provincia de Buenos AiresInstituto de Fisiologia Vegetal     

Influence of Rhizobial inoculation on yield of wheat (Triticum aestivum L.)

Summary Soil + charcoal (1∶3) carrier based and liquid cultures of Rhizobia were used to inoculate wheat seed cv. HD2329. The plants received 100 kg N in two equal splits and 60 kg P₂O₅ and 40 kg K₂₀ ha⁻¹. Inoculation with rhizobia had little effect on grain yield of wheat. Significant increase in straw yield and N-uptake occurred due to inoculation. A comparison of results of a similar experiment conducted during 1983–84, showed that inoculation with the same strains of rhizobia and application 50 kg N ha⁻¹ as basal dressing, was more effective in increasing yield and N-uptake in wheat cv. HD2329. It appears reasonable to assume occurrence of nitrogen fixation by root nodule bacteria in rhizosphere of wheat.     

Assessment of grain yield indices in response to drought stress in wheat (Triticum aestivum L.)

Drought stress constricts crop production in the world. Increasing human population and predicted temperature increase owing to global warming will lead ruthless problems for agricultural production in near future. Hence, use of high yielding genotypes having drought tolerance and scrutinize of drought sensitive local cultivars for making them tolerant may be the proficient approaches to cope its detrimental outcomes. The current study was executed during 20015–2016 and 2016–2017 in field using randomized complete block design under factorial arrangements on 50 wheat genotypes for exploring their sensitivity and tolerance against drought. Some of the attributes of grain yield and drought tolerance indices were recorded. Grain yield showed negative correlations with tolerance index (TOL), drought index (DI) and stress susceptibility index (SSI) while positive correlation with mean productivity (MP) and geometric mean productivity (GMP) under drought condition. These findings depicted that tolerant genotypes could be chosen by high MP and GMP values and low SSI and TOL values. Based on the results, genotypes GA-02, Faisalabad-83, 9444, Sehar-06, Pirsabak-04 and Kohistan-97 were more tolerant and recognized as suitable for both normal and drought conditions. Genotypes of Chenab-00, Kohsar-95, Parwaz-94 and Kohenoor-83 confirmed more sensitive due to high grain yield loss under drought stress.     

Diallelic analysis of quantitative traits in hexaploid wheat (Triticum aestivum L.)

Abstract

A complete diallel study of crosses between eight wheat varieties was carried out to determine the relative magnitude of components of genetic variation and heritability for important grain yield, quality and drought‐related traits. The data appeared adequate for the additive‐dominance model. The additive effects predominated for most traits, and consequently the narrow‐sense heritability was high to moderately high for flag leaf area, weight and venation, stomatal frequency and size, epidermal cell size, biomass, protein content, number of tillers, spike length, spike density, 1000‐grain weight and grain yield. These results appear promising for selecting better plants in the segregating populations with some degree of improvement for yield, quality and physiological efficiency.     

耕作措施对冬小麦田杂草生物多样性及产量的影响

在连续5a秸秆全量还田的免耕、旋耕、耙耕、深松和常规耕作试验地中,设置了除草和不除草处理,研究了其对杂草总密度、优势杂草种类、生物多样性指数和冬小麦产量的影响,并分析了杂草与小麦间的竞争关系。结果表明,麦田杂草主要有7种,分别是麦蒿(Descuminia sophia (L.) Webb ex Prantl)、荠菜(Capsella bursa-pastoris (L.) Medik)、燕麦(Avena sativa L.)、田旋花(Convolvulus arvensis L.)、刺儿菜(Cirsium setosum (Willd.) Bieb.)、繁缕(Stellaria media (L.) Vill.)、麦家公(Lithospermum arvense L.)。在未除草条件下,免耕、深松的杂草总密度显著提高;而在除草条件下,杂草密度显著下降。免耕、深松、常规耕作在未除草条件下,优势杂草种类为麦蒿、荠菜,旋耕、耙耕条件下的优势杂草为麦蒿;而除草后各处理的优势杂草均只有麦蒿。耙耕、常规耕作措施在未除草条件下杂草群落具有较高的物种丰富度和均匀度。无论哪种耕作措施,除草能提高冬小麦产量,其中以深松耕作结合除草处理的小麦产量最高。在小麦抽穗期,未除草处理杂草株高接近或高于小麦株高,会造成杂草与小麦间的光竞争,对小麦的生长状况有显著影响,从而导致小麦产量降低。     

Carbon balance assessment of a Belgian winter wheat crop (Triticum aestivum L.)

The carbon balance of a winter wheat crop in Lonzée, Belgium, was assessed from measurements carried out at different spatial and temporal scales between November 2004 and August 2005. From eddy covariance measurements, the net ecosystem exchange was found to be ?0.63 kg C m^?2 and resulted from the difference between gross primary productivity (GPP) (?1.58 kg C m^?2) and total ecosystem respiration (TER) (0.95 kg C m^?2). The impact of the u_* threshold value on these fluxes was assessed and found to be very small. GPP assessment was partially validated by comparison with an estimation scaled up from leaf scale assimilation measurements. Soil respiration (SR), extrapolated from chamber measurements, was 0.52 kg C m^?2. Net primary productivity, assessed from crop sampling, was ?0.83 kg C m^?2. By combining these fluxes, the autotrophic and heterotrophic components of respiration were deduced. Autotrophic respiration dominated both TER and SR. The evolution of these fluxes was analysed in relation to wheat development.     

水肥不同层次组合对冬小麦（Triticum aestivum L.）氮磷养分有效性和产量效应的影响

以肥熟土垫旱耕人为土为供试土样,用分层土柱试验法研究了不同层次水分、氮、磷组合对冬小麦(Triticum aestivum L.)氮磷养分有效性和产量效应的影响.结果表明,不同土层水肥处理的氮磷养分有效性和产量效应差异显著.氮素养分有效性在4.73%～41.19%之间,磷素养分有效性在4.11%～13.58%之间.对氮素养分有效性,单施氮整体湿润时(0～90cm土层湿润)较上干下湿(0～30cm土层干旱胁迫,30～90cm土层湿润)低4.87%,而氮磷配施在整体湿润时较上干下湿高6.38%,差异均达显著水平;对磷素养分有效性,氮磷配施时,在整体湿润时较上干下湿增加5.01T(p<0.05).从不同施肥土层看,氮素养分有效性均以0～90cm土层施肥处理最高;对氮磷配施处理,在上干下湿时分别比0～30cm、30～60cm和60～90cm土层施肥处理高9.5%、10.1%和20.2个%;对磷素养分有效性,整体湿润处理,以0～30cm土层施肥显著高于其它土层施肥处理.单施氮或磷,上干下湿时氮磷养分的产量效应均高于整体湿润处理,但氮磷配施时均以整体湿润处理较高;从不同土层施肥看,氮素养分的产量效应以0～90cm土层施肥最高;磷素养分的产量效应则表现为0～90cm与0～30cm土层施肥处理显著高于30～60cm和60～90cm土层施肥处理.分析0～90cm土层残留硝态氮和有效磷累积量可以看出,不同处理土壤残留硝态氮含量存在显著差异,上干下湿时CK、单施氮、单施磷和氮磷配施土壤残留硝态氮分别比整体湿润相应施肥处理增加125.8%、20.1%、21.9%和2.1%;不同处理有效磷差异性不及硝态氮明显.整体看,在两种水分状况下,均以0～90cm和0～30cm土层施肥有利于提高氮磷养分对冬小麦的有效性和产量效应,减少硝态氮和有效磷在土壤中的残留累积.考虑到生产上的可操作性,仍以施入0～30cm土层最适,说明即使在上干下湿情况下,保证上层有效养分供应仍具重要作用.     

Quantitative-genetic analysis of reciprocal crosses between a winter and a spring cultivar of common wheat (Triticum aestivum L.)

The winter wheat cultivar Sakhalin (parent A) and the spring wheat cultivar Khush-hal (parent B), assumed to be both nuclear-genetically and plasmotypically different, were reciprocally crossed and the F₁ generation of the reciprocals backcrossed to either parent. The populations (AxB)F₁, (AxB)F₂, [(AxB)F₁xA]F₁ and [(AxB)F₁xB]F₁, and their reciprocals (BxA)F₁, (BxA)F₂, [(BxA)F₁xA]F₁ and [(BxA)F₁xB]F₁, assumed to have the plasmotypes of the parents A and B respectively, were spring sown in the same field from unvernalized (experiment #1) and vernalized (experiment #2) seeds. The results of the analyses of variance of the data recorded in the two experiments are fairly similar. In both the experiments the plasmotypically A populations have produced more heads and higher grain yields per plant than their plasmotypically B reciprocals. The components of the family means and of half the differences between the reciprocals within the families show that vernalization has not affected the efficiency of the nuclear genes of parent A but has reduced the efficiency of the nuclear genes of parent B in both the homozygous and the heterozygous states. This in turn has affected the components of family mean squares and those of the family x reciprocals interaction mean squares in the analysis of variance tables.     

Comparison of the effects of symmetric and asymmetric temperature elevation and CO2 enrichment on yield and evapotranspiration of winter wheat (Triticum aestivum L.)

Under the changing climate, asymmetric warming pattern would be more likely during day and night time, instead of symmetric one. Concurrently, the growth responses and water use of plants may be different compared with those estimated based on symmetric warming. In this work, it was compared with the effects of symmetric (ETs) and asymmetric (ETa) elevation of temperature alone, and in interaction with elevated carbon dioxide concentration (EC), on the grain yield (GY) and evapotranspiration in winter wheat (Triticum aestivum L.) based on pot experiment in the North China Plain (NCP). The experiment was carried out in six enclosed‐top chambers with following climate treatments: (1) ambient temperature and ambient CO₂ (CON), (2) ambient temperature and elevated CO₂ (EC), (3) elevated temperature and ambient CO₂ (ETs; ETa), and (4) elevated temperature and elevated CO₂ (ECETs, ECETa). In symmetric warming, temperature was increased by 3°C and in asymmetric one by 3.5°C during night and 2.5°C during daytime, respectively. As a result, GY was in ETa and ETs 15.6 (P < 0.05) and 10.3% (P < 0.05) lower than that in CON. In ECETs and ECETa treatments, GY was 14.9 (P < 0.05) and 9.1% (P < 0.05) higher than that in CON. Opposite to GY, evapotranspiration was 7.8 (P < 0.05) and 17.9% (P < 0.05) higher in ETa and ETs treatments and 7.2 (P < 0.05) and 2.1% (P > 0.05) lower in ECETs and ECETa treatments compared with CON. Thus, GY of wheat could be expected to increase under the changing climate with concurrent elevation of CO₂ and temperature as a result of increased WUE under the elevated CO₂. However, the gain would be lower under ETa than that estimated based on ETs due to higher evapotranspiration.     

Effects of bio fertilizer and nano Zn-Fe oxide on physiological traits,antioxidant enzymes activity and yield of wheat (Triticum aestivum L.) under salinity stress

In order to evaluate the effects of nano Zn-Fe oxide and bio fertilizer on physiological traits, antioxidant activity and yield of wheat under salinity stress, a factorial experiment was conducted based on RCBD with three replications.Treatments were included salinity in three levels (no-salt, salinity 25 and 50 mM NaCl), four bio fertilizers levels (no bio fertilizer, seed inoculation by Azotobacter, Azosperilium, Pseudomonas) and nano oxide (without nano, application of nano Zn oxide, nano Fe oxide and nano Fe-Zn oxide 1.5 g/lit). Salinty stress decreased the chlorophyll-a, chlorophyll-b, total chlorophyll, photochemical efficiency of PSII and yield of wheat, whearas electrical conductivity, soluble sugars, proline content, and the activities of Catalase (CAT), Peroxidase (POD) and Polyphenol Oxidase (PPO) enzymes increased. Similar results were observed in CAT, POD and PPO activities due to inoculation by bio fertilizers and nano oxide. Maximum of soluble sugars and proline content were observed in the highest salinity level and application of Pseudomonas. Application of nano Zn-Fe oxide increased about 17.40% from grain yield in comparision with no application of nano oxide in the highest salinity level. Generally, it was conducted that bio fertilizer and nano oxide can be used as a proper tool for increasing wheat yield under salinity condition.     

Impact of elevated ozone concentration on growth,physiology, and yield of wheat (Triticum aestivum L.): a meta‐analysis

We quantitatively evaluated the effects of elevated concentration of ozone (O₃) on growth, leaf chemistry, gas exchange, grain yield, and grain quality relative to carbon‐filtered air (CF) by means of meta‐analysis of published data. Our database consisted of 53 peer‐reviewed studies published between 1980 and 2007, taking into account wheat type, O₃ fumigation method, rooting environment, O₃ concentration ([O₃]), developmental stage, and additional treatments such as drought and elevated carbon dioxide concentration ([CO₂]). The results suggested that elevated [O₃] decreased wheat grain yield by 29% (CI: 24–34%) and aboveground biomass by 18% (CI: 13–24%), where CI is the 95% confidence interval. Even in studies where the [O₃] range was between 31 and 59 ppb (average 43 ppb), there was a significant decrease in the grain yield (18%) and biomass (16%) relative to CF. Despite the increase in the grain protein content (6.8%), elevated [O₃] significantly decreased the grain protein yield (?18%). Relative to CF, elevated [O₃] significantly decreased photosynthetic rates (?20%), Rubisco activity (?19%), stomatal conductance (?22%), and chlorophyll content (?40%). For the whole plant, rising [O₃] induced a larger decrease in belowground (?27%) biomass than in aboveground (?18%) biomass. There was no significant response difference between spring wheat and winter wheat. Wheat grown in the field showed larger decreases in leaf photosynthesis parameters than wheat grown in < 5 L pots. Open‐top chamber fumigation induced a larger reduction than indoor growth chambers, when plants were exposed to elevated [O₃]. The detrimental effect was progressively greater as the average daily [O₃] increased, with very few exceptions. The impact of O₃ increased with developmental stages, with the largest detrimental impact during grain filling. Both drought and elevated [CO₂] significantly ameliorated the detrimental effects of elevated [O₃], which could be explained by a significant decrease in O₃ uptake resulting from decreased stomatal conductance.     

The ameliorative effects of exogenously applied proline on physiological and biochemical parameters of wheat (Triticum aestivum L.) crop under copper stress condition

The presence of significant amount of heavy metals in rivers and canals due to mixing of untreated industrial effluents is a common phenomenon, especially in developing countries. The agricultural crops are influenced by the presence of various pollutants in the sewage, being applied for irrigation purpose. The effluents containing copper affect the growth and development of crop species, thereby, ought to be mitigated by foliar spray of osmoprotectants, e.g. proline. A pot culture experiment was conducted at the University of Agriculture, Faisalabad-Pakistan during the crop season 2015–2016. The treatments consisted of (a) three wheat varieties (Punjab-96, MH-97, FSD-83), (b) two levels of copper (0, 400?µM) applied through rooting medium, and (c) two levels of proline (0, 80?mM) applied through foliar application. The treatments were arranged in a completely randomized design with four replications. The results showed that application of 400?µM copper caused a reduction in biomass accumulation, chlorophyll (‘a’ and ‘b’) contents, and eventually yield (100-grain weight). There were also significant decreases in gas exchange parameters (stomatal conductance, internal CO₂ concentration), photosynthetic rate, water-use-efficiency, and transpiration rate in response to copper stress. Metal toxicity caused the maximum reduction in productivity of PSII, electron transport rate, and photochemical quenching, while higher values of non-photochemical quenching were recorded in the wheat varieties. The activities of antioxidant enzymes (superoxide dismutase, catalase, peroxidase), as well as quantities of proline, protein and calcium contents were accelerated in response to copper stress. The uptake of calcium, magnesium, and potassium constituents by plants was reduced, while assimilation of calcium was increased in plants under copper stress. However, the occurrence of negative effects on these parameters due to copper stress was mitigated by foliar spray of proline at the rate of 80?mM solution. The exogenous application of proline at the rate of 80?mM resulted in the reduction of generation of reactive oxygen species and enhanced accumulation of proline and protein contents in wheat varieties under copper stress environment.     

The effect of humus fractions on the phosphorylase activity of wheat (Triticum aestivum L.)

The liberation of phosphoric acid from glucose-1-phosphate, catalyzed by phosphorylase was studied in wheat growing in sand cultures with an addition of humic acid and hymatomelanic acid. It was found that the phosphorylase activity of tissues changes under the influence of humic acid very significantly. The maximum activity is reached at 10 mg humic acid/liter. The overground organs are less sensitive, as a stimulation effect is reached there only at 400 mg/liter. The effect of hymatomelanic acid is negligible in comparison with that of humic acid. The observed phenomenon is related to the effect of humus substances on the equilibrium of saccharides and on the distribution of dry matter in the plant.     

A SNP-based genetic dissection of versatile traits in bread wheat (Triticum aestivum L.)

The continuous increase in global population prompts increased wheat production. Future wheat (Triticum aestivum L.) breeding will heavily rely on dissecting molecular and genetic bases of wheat yield and related traits which is possible through the discovery of quantitative trait loci (QTLs) in constructed populations, such as recombinant inbred lines (RILs). Here, we present an evaluation of 92 RILs in a bi-parental RIL mapping population (the International Triticeae Mapping Initiative Mapping Population [ITMI/MP]) using newly generated phenotypic data in 3-year experiments (2015), older phenotypic data (1997–2009), and newly created single nucleotide polymorphism (SNP) marker data based on 92 of the original RILs to search for novel and stable QTLs. Our analyses of more than 15 unique traits observed in multiple experiments included analyses of 46 traits in three environments in the USA, 69 traits in eight environments in Germany, 149 traits in 10 environments in Russia, and 28 traits in four environments in India (292 traits in 25 environments) with 7584 SNPs (292 × 7584 = 2 214 528 data points). A total of 874 QTLs were detected with limit of detection (LOD) scores of 2.01–3.0 and 432 QTLs were detected with LOD > 3.0. Moreover, 769 QTLs could be assigned to 183 clusters based on the common markers and relative proximity of related QTLs, indicating gene-rich regions throughout the A, B, and D genomes of common wheat. This upgraded genotype–phenotype information of ITMI/MP can assist breeders and geneticists who can make crosses with suitable RILs to improve or investigate traits of interest.     

Molecular mapping of quantitative trait loci for yield and yield components in spring wheat (Triticum aestivum L.)

An F1 derived doubled haploid (DH) population of 402 lines from the adapted spring wheat cross Superb (high yielding)/BW278 (low yielding) was developed to identify quantitative trait loci (QTL) associated with yield and yield components. A subset of the population (186 lines) was evaluated in replicated field trials in 2001 and 2002 at six locations in Manitoba and Saskatchewan, Canada. Agronomic parameters, grain yield and yield components including 1,000 grain weight, harvest index, average seed weight spike(-1), seed number spike(-1) and spikes number m(-2) were measured. A genetic map was constructed with 268 microsatellite marker loci and included two morphological genes, reduced plant height, Rht-B1b, and the presence/absence of awns, B1. Composite interval mapping was conducted to estimate the location and effect of QTL associated with the evaluated traits. A total of 53 QTL were identified on 12 chromosomes for the 9 evaluated traits with the coefficient of determination ranging from 0.03 to 0.21 of the total variation. The increase in yield and yield components ranged from 4.5 to 17.1% over the population mean. The five grain yield QTL were detected on chromosomes 1A, 2D, 3B, and 5A and showed a combined increase of 34.4%, over the population mean. The alleles from Superb were associated with increased yield for four of the five QTL. This study identified potential chromosome segments for use in marker-assisted selection to improve yield and yield components in spring wheat.     

An assessment of the relative effects of adverse physical and chemical properties of sodic soil on the growth and yield of wheat (Triticum aestivum L.)

Two wheat varieties were grown in artificially created sodic soils in pots at a range of sodicity levels (exchangeable sodium percentage (ESP) 15–52), with and without an anionic polyacrylamide soil conditioner (PAM) to stabilise soil aggregates. Increasing sodicity decreased the % water stable aggregates (% WSA) in soil and survival, grain and straw yield of wheat. Plants grown at high sodicity also had higher Na⁺, lower K⁺ and Ca²⁺ concentrations and lower K⁺/Na⁺ ratio in flag leaf sap than plants grown in control (non-sodic) soil. Sodicity had no effect on the concentrations of Cu²⁺, Fe²⁺, Mn²⁺ and Zn²⁺ in grains and straw, but total uptake of these micronutrients was deceased due to lower dry weight of these tissues per plant. At all sodicity levels treatment of sodic soil with PAM increased the % WSA to values greater than in the non-sodic control soil, and slightly lowered ESP. Over the range ESP 15–44 the effects of PAM on wheat grain yield increased as sodicity increased, so that at ESP 44 grain yield in the treatment with PAM was only 25% lower than in the non-sodic control. However at ESP 52 the effects of PAM were smaller, and grain yield was 86% lower than in the control. At this sodicity level the decreases in grain yield due to sodicity and the increases in reponse to treatment of sodic soil with PAM were similar in the two varieties tested. At high sodicity levels (ESP 44 and 52) treatment of sodic soil with PAM decreased the concentration of Na⁺ and increased K⁺ and K⁺/Na⁺ ratio in flag leaf sap. However, at the highest sodicity level (ESP 52), flag leaf Na⁺ concentration remained above the level (100 mol m^-3) at which it has been found to be toxic. Concentrations of Cu²⁺, Fe²⁺, Mn²⁺ and Zn²⁺ in grain and straw were unaffected by PAM. These results suggest that at ESP up to 40–50 adverse physical characteristics are the major cause of low wheat yield in sodic soils, either due to their direct effects in decreasing growth, or their indirect effects in increasing uptake of Na⁺ and decreasing uptake of K⁺. Above ESP 50, roots are less able to exclude Na⁺, even in the presence of improved soil physical conditions, so that at these sodicity levels, both adverse physical and adverse chemical properties contribute to the decreased yield. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of ovary-conditioned medium on microspore embryogenesis in common wheat (Triticum aestivum L.)

Microspores were isolated from wheat (Triticum aestivum L.) spikes of various genotypes following an effective pretreatment that induced microspore embryogenesis. The isolated microspores were cultured with or without live ovaries, and with or without medium pre-conditioned by ovaries for varying periods of time. Live ovaries alone increased androgenic embryoid yields up to 4.5-fold over the control for microspores isolated from responsive genotypes. While live ovary co-culture alone was not effective for microspores isolated from recalcitrant genotypes, the addition of medium preconditioned by ovaries to microspore cultures increased embryoid yield by more than 100-fold. Without ovary-conditioned medium, no embryoids could be obtained from some recalcitrant genotypes. Ovary-conditioned medium apparently functions to increase embryoid yields by providing essential substance(s) for elaboration of the embryogenic program already triggered during pretreatment.     

Effects of elevated carbon dioxide and ozone on the growth and yield of spring wheat (Triticum aestivum L.)

Spring wheat cv. Minaret was grown under three carbon dioxide(CO₂) and two ozone (O₃) concentrations from seedling emergenceto maturity in open-top chambers. Under elevated CO₂ concentrations,the green leaf area index of the main shoot was increased, largelydue to an increase in green leaf area duration. Biomass increasedlinearly in response to increasing CO₂ (ambient, 550 and 680ppm). At anthesis, stem and ear dry weights and plant heightwere increased by up to 174%, 5% and 9 cm, respectively, andbiomass at maturity was 23% greater in the 680 ppm treatmentas compared to the ambient control. Grain numbers per spikeletand per ear were increased by 0.2 and 5 grains, respectively,and this, coupled with a higher number of ears bearing tillers,increased grain yield by up to 33%. Exposure to a 7 h daily mean O₃ concentration of 60 ppb inducedpremature leaf senescence during early vegetative growth (leaves1–7) under ambient CO₂ concentrations. Damage to the mainshoot and possible seedling mortality during the first 3 weeksof exposure altered canopy structure and increased the proportionof tillers 1 and 2 which survived to produce ears at maturitywas increased; as a result, grain yield was not significantlyaffected. In contrast to the older leaves, the flag leaf (leaf8) sustained no visible O₃ damage, and mean grain yield perear was not affected. Interactions between elevated CO₂ andO₃ influenced the severity of visible leaf damage (leaves 1–7),with elevated CO₂ apparently protecting against O₃-induced prematuresenescence during early vegetative growth. The data suggestthat the flag leaf of Minaret, a major source of assimilateduring grain fill, may be relatively insensitive to O₃ exposure.Possible mechanisms involved in damage and/or recovery are discussed. Key words: Carbon dioxide, ozone, spring wheat (cv. Minaret), leaf damage, tiller, yield