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Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a re-emerging disease, posing a threat to wheat production. In Spain, stem rust has been rarely detected since the 1970s, but infection was observed in wheat fields in 2018. We analysed six stem rust samples collected in Rota, Cádiz province and one from Monteagudo del Castillo, Teruel province. All the samples from Rota were typed as race TKTTF, whereas the sample from Monteagudo del Castillo, collected in a wheat field adjacent to barberry bushes, was typed as race TKHBK. This race has a unique and significant virulence combination that includes virulence to Sr31, Sr33, Sr53 and Sr59, and is avirulent to Rusty, a durum line developed for universal susceptibility to the wheat stem rust pathogen. TKHBK is the first race outside the Ug99 race group with virulence to Sr31 and the first known race with virulence to Sr59. Genotyping studies indicate that race TKHBK does not belong to the Ug99 or TKTTF race groups and constitutes a previously unknown lineage. Two hundred bread and durum wheat cultivars and breeding lines from Spain were evaluated against TKHBK, TKTTF, and six additional races. Resistance was observed to all the races evaluated. Molecular markers confirmed the presence of Sr7a, Sr24, Sr31, Sr38 and Sr57 in bread wheat, and Sr13 in durum wheat. The re-emergence of wheat stem rust in Spain and the occurrence of unique virulences underscore the need to continue surveying and monitoring this disease. info:eu-repo/semantics/acceptedVersion

Hypothesis/Gap Statement. The impacts of increased biomarker testing on antifungal prescribing have not yet been fully examined in a real-life setting.Objectives. Biomarkers for invasive fungal disease (IFD) have been shown to reduce antifungal prescriptions in neutropaenic haemato-oncology patients. Our study aimed to assess the real-life impacts of introducing a novel biomarker-based pathway, incorporating serum galactomannan and Aspergillus PCR, for pyrexial haemato-oncology admissions.Methods. Patients with neutropaenic fever were identified prospectively after introduction of the new pathway from 2013-2015. A historical group of neutropaenic patients who had blood cultures taken from 2009-2012 was generated for comparison. Clinical details, including demographics, underlying diagnosis, investigations, radiology and antimicrobial treatment were obtained.Results. Prospective data from 308 patients were compared to retrospective data from 302 patients. The proportion of patients prescribed an antifungal medication was unchanged by the pathway (P=0.79), but the pattern was different, with more patients receiving targeted antifungals (P=0.04). A negative serum galactomannan test was not sufficient evidence to withhold therapy, with 17.2% of these episodes felt to have possible or probable IFD using the European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group (EORTC/MSG) criteria. There was no difference in 30-day mortality (P=0.21) or 1-year mortality (P=0.57) following introduction of the pathway.Conclusions. Biomarkers can be used safely as part of a multidisciplinary approach to the diagnosis of IFD in neutropaenic haemato-oncology patients. Whilst they do not necessarily result in antifungal therapy being withheld, they can allow more confident diagnosis of IFD and more specific antifungal therapy in selected cases., Conflicts of Interest AWM is supported by the Wellcome Trust. DAE has received funding from MSD, Astellas, Gilead, Pfizer – none of these are related to this submission. Funding Information This study was funded by Pfizer and Gilead.

Concerns about the effects of global warming on crop yields have been raised due to stagnating yield progress in recent years. However, an understanding of the effects of changes in temperature and rainfall throughout the crop cycle on historical yield progress is lacking in Europe (EU). In this study, positive wheat, barley, rice, and maize yield progress in the EU (1961–2019) was significant, with rates of 0.05, 0.04, 0.05, and 0.07 Tha−1year−1, for the four crops respectively. Much of this progress has been sustained by Eastern European countries (EE), which had the highest yield progress rates. On average, in the case of wheat and barley, a temperature increase of 1°C in the winter resulted in yields increasing by +0.33 Tha−1 in EE. This was potentially due to decreasing cold damage and improved photosynthesis and vegetative growth, supporting positive yield progress. Recent historical (2001–2019) rates of wheat, barley, rice, and maize yield progress were positive in all EU regions except Western Europe (WE), barley in Southern Europe (SE) and wheat in Northern Europe (NE). Stagnated wheat, barley and rice yields in WE were not explained by temperature or rainfall using direct correlations of observed data. However, May and July temperatures were associated with wheat yields in NE (−0.30 Tha−1°C−1), barley in SE (−0.14 Tha−1°C−1) and maize in WE and SE (−0.42 and −0.39 Tha−1°C−1). With increasing temperatures becoming less than optimal for photosynthesis, reducing grain filling duration and increasing drought episodes, crop yields have stagnated for wheat in NE and barley in SE. With consistent increases in temperature and water evaporative demand expected in the future, the interplay among genetic adaptation, increased crop cycle duration, drought tolerance, sowing dates, smart irrigation and sustainable practices may require thorough regional testing to maximise the yields of wheat, barley and maize in Europe. info:eu-repo/semantics/publishedVersion

Understanding the environmental and genetic factors behind the adaptation of landraces to different environments may help design breeding strategies and to promote yield improvement. Based on previous results that showed a differential frequency of alleles associated with important agronomic traits in landraces that originated in the east (EM) and the west (WM) of the Mediterranean Basin, this study analysed their patterns of adaptation and the influence this adaptation has on yield formation strategies. Thirteen and thirty-one genotypes selected according to their membership coefficient (q>0.900) from the EM and the WM genetic subpopulations, respectively, were tested during six crop seasons under rainfed Mediterranean conditions. Yearly yields ranged from 3173 to 4917 kg/ha. EM landraces showed more spikes per unit area, while WM ones showed consistently taller plants, larger cycle length to anthesis, a shorter grain filling period, a higher grain filling rate and heavier grains. The contrasting pattern of adaptation of the two subpopulations was based on a differential ability to use the water available before and after anthesis. The yield of EM landraces, originated in the warmest and driest area of the Mediterranean basin, relied mostly on water input before anthesis, which was beneficial for spike production and for the accumulation of water-soluble carbohydrates in the stems prior to anthesis, to be remobilized to grains during grain filling. WM landraces performed better in environments with high water input during grain filling, which was efficiently used to increase grain setting and produce heavy grains. EM landraces could be used in breeding to improve the adaptation of modern varieties to terminal drought. info:eu-repo/semantics/publishedVersion

Identifying mechanisms and pathways involved in gene-environment interplay and phenotypic plasticity is a long-standing challenge. It is highly desirable to establish an integrated framework with an environmental dimension for complex trait dissection and prediction. A critical step is to identify an environmental index that is both biologically relevant and estimable for new environments. With extensive field-observed complex traits, environmental profiles, and genome-wide single nucleotide polymorphisms for three major crops (maize, wheat, and oat), we demonstrated that identifying such an environmental index (i.e., a combination of environmental parameter and growth window) enables genome-wide association studies and genomic selection of complex traits to be conducted with an explicit environmental dimension. Interestingly, genes identified for two reaction-norm parameters (i.e., intercept and slope) derived from flowering time values along the environmental index were less colocalized for a diverse maize panel than for wheat and oat breeding panels, agreeing with the different diversity levels and genetic constitutions of the panels. In addition, we showcased the usefulness of this framework for systematically forecasting the performance of diverse germplasm panels in new environments. This general framework and the companion CERIS-JGRA analytical package should facilitate biologically informed dissection of complex traits, enhanced performance prediction in breeding for future climates, and coordinated efforts to enrich our understanding of mechanisms underlying phenotypic variation.

Wheat adaptability to a wide range of environmental conditions is mostly determined by allelic diversity within genes controlling vernalization requirement (Vrn-1) and photoperiod sensitivity (Ppd-1). We characterized a panel of 151 durum wheat Mediterranean landraces and 20 representative locally adapted modern cultivars for their allelic composition at Vrn-1 and Ppd-1 gene using diagnostic molecular markers and studied their association with the time needed to reach six growth stages under field conditions over 6 years. Compared with the more diverse and representative landrace collection, the set of modern cultivars were characterized by a reduction of 50% in the number of allelic variants at the Vrn-A1 and Vrn-B1 genes, and the high frequency of mutant alleles conferring photoperiod insensitivity at Ppd-A1, which resulted on a shorter cycle length. Vrn-A1 played a greater role than Vrn-B1 in regulating crop development (Vrn-A1 > Vrn-B1). The results suggest that mutations in the Vrn-A1 gene may have been the most important in establishing the spring growth habit of Mediterranean landraces and modern durum cultivars. The allele Vrn-A1d, found in 10 landraces, delayed development. The relative effects of single Vrn-A1 alleles on delaying the development of the landraces were vrn-A1 = Vrn-A1d > Vrn-A1b > Vrn-A1c. Allele vrn-B1 was present in all except two landraces and in all modern cultivars. The null allele at Ppd-A1 (a deletion first observed in the French bread wheat cultivar ‘Capelle-Desprez’) was found for the first time in durum wheat in the present study that identified it in 30 landraces from 13 Mediterranean countries. Allele Ppd-A1a (GS105) was detected in both germplasm types, while the allele Ppd-A1a (GS100) was found only in modern North American and Spanish cultivars. The relative effect of single Ppd-A1 alleles on extending phenological development was Ppd-A1(DelCD) > Ppd-A1b > Ppd-A1a (GS105) > Ppd-A1a (GS100). Sixteen Vrn-1+Ppd-1 allelic combinations were found in landraces and six in modern cultivars, but only three were common to both panels. Differences in the number of days to reach anthesis were 10 days in landraces and 3 days in modern cultivars. Interactive effects between Vrn-1 and Ppd-1 genes were detected.

Previous research has shown that progress in genetic yield potential is associated with adaptation to agronomic planting density, though its genetic basis has not been addressed before. In the current study, a wheat (Triticum aestivum L.) association mapping initiative (WAMI) panel of 287 elite lines was assessed for the effects of plant density on grain yield (YLD), 1000-kernel weight (TKW), and grain number (GNO) in yield plots consisting of four evenly spaced rows. The YLD and GNO of inner (high plant density) rows compared with outer rows (low plant density) indicated a consistent pattern: genotypes that performed best under intense competition (inner rows) responded less to reduced competition (outer rows) while being generally the best performers on aggregate (inner plus outer rows). However, TKW was not affected by plant density. To identify the genetic loci, an adaptation to density index (ADi) was computed as the scaled difference in trait values between inner and outer rows. Results on biplot analysis indicated that ADi was correlated with YLD in high-yielding environments, suggesting that it is a component of high yield potential. Genotyping of the WAMI panel was done through 90K Illumina Bead single nucleotide polymorphism (SNP) array. Association mapping employed using 18,104 SNP markers for ADi identified a major locus in chromosome 3B at 71 cM that explained 11.4% variation in ADi for YLD and GNO. Functional marker for ADi will enable identification of the trait in early generations—not otherwise possible in spaced plants typical of pedigree breeding approach—and to select parents for hybrid development.

Unfortunately, the Fig. 1 of this original article was incorrectly published. The corrected Fig. 1 is given below.

The wheat association mapping initiative is appropriate for gene discovery without the confounding effects of phenology and plant height. The wheat association mapping initiative (WAMI) population is a set of 287 diverse advanced wheat lines with a narrow range of variation for days to heading (DH) and plant height (PH). This study aimed to characterize the WAMI and showed that this diverse panel has a favorable genetic background in which stress adaptive traits and their alleles contributing to final yield can be identified with reduced confounding major gene effects through genome-wide association studies (GWAS). Using single nucleotide polymorphism (SNP) markers, we observed lower gene diversity on the D genome, compared with the other genomes. Population structure was primarily related to the distribution of the 1B.1R rye translocation. The narrow range of variation for DH and PH in the WAMI population still entailed segregation for a few markers associated with the former traits, while Rht genes were associated with grain yield (GY). Genotype by environment (G × E) interaction for GY was primarily explained by Rht-B1, Vrn-A1 and markers on chromosomes 2D and 3A when running GWAS with genotype scores from the G × E biplot. The use of PC scores from the G × E biplot seems a promising tool to determine genes and markers associated with complex interactions across environments. The WAMI panel lends itself to GWAS for complex trait dissection by avoiding the confounding effects of DH and PH which were reduced to a minimum (using Rht-B1 and Vrn-A1 scores as covariables), with significant associations with GY on chromosomes 2D, 3A and 3B.

Through genome-wide association study, loci for grain yield and yield components were identified in chromosomes 5A and 6A in spring wheat (Triticum aestivum). Genome-wide association study (GWAS) was conducted for grain yield (YLD) and yield components on a wheat association mapping initiative (WAMI) population of 287 elite, spring wheat lines grown under temperate irrigated high-yield potential condition in Ciudad Obregon, Mexico, during four crop cycles (from 2009–2010 to 2012–2013). The population was genotyped with high-density Illumina iSelect 90K single nucleotide polymorphisms (SNPs) assay. An analysis of traits across subpopulations indicated that lines with 1B/1R translocation had higher YLD, grain weight, and taller plants than lines without the translocation. GWAS using 18,704 SNPs identified 31 loci that explained 5–14 % of the variation in individual traits. We identified SNPs in chromosome 5A and 6A that were significantly associated with yield and yield components. Four loci were detected for YLD in chromosomes 3B, 5A, 5B, and 6A and the locus in 5A explained 5 % of the variation for grain number/m2. The locus for YLD in chromosome 6A also explained 6 % of the variation in grain weight. Loci significantly associated with maturity were identified in chromosomes 2B, 3B, 4B, 4D, and 6A and for plant height in 1A and 6A. Loci were also detected for canopy temperature at grain filling (2D, 4D, 6A), chlorophyll index at grain filling (3B and 6A), biomass (3D and 6A) and harvest index (1D, 1B, and 3B) that explained 5–10 % variation. These markers will be further validated.

Identifying markers for physiological traits of proven value in breeding, especially ones that are consistent across environments with different patterns of stress, strengthens the toolkit to increase confidence in the value and delivery from physiological breeding. To identify markers relevant to drought adaptation, this review will highlight the importance of development and implementation of robust and repeatable phenotyping that is relevant to the different target drought types, and practical examples of managed environment facilities in Australia and Mexico are given. These facilities can be used as models to: (i) improve reliability and consistency of environments and genetic responses to the environment at a global scale; (ii) improve the capacity to deliver quantitative trait loci (QTLs) as user-friendly markers for enriching populations; and (iii) illustrate the use of populations with a narrow range of variation for phenology allowing the identification of QTLs for drought-adaptive traits. However, the importance of further optimizing phenology and plant height at a global scale is highlighted. Finally, the impact of physiological trait-based crossing is demonstrated and supports the need for urgent development of robust genetic markers.

A stable QTL that may be used in marker-assisted selection in wheat breeding programs was detected for yield, yield components and drought tolerance-related traits in spring wheat association mapping panel. Genome-wide association mapping has become a widespread method of quantitative trait locus (QTL) identification for many crop plants including wheat (Triticum aestivum L.). Its benefit over traditional bi-parental mapping approaches depends on the extent of linkage disequilibrium in the mapping population. The objectives of this study were to determine linkage disequilibrium decay rate and population structure in a spring wheat association mapping panel (n = 285–294) and to identify markers associated with yield and yield components, morphological, phenological, and drought tolerance-related traits. The study was conducted under fully irrigated and rain-fed conditions at Greeley, CO, USA and Melkassa, Ethiopia in 2010 and 2011 (five total environments). Genotypic data were generated using diversity array technology markers. Linkage disequilibrium decay rate extended over a longer genetic distance for the D genome (6.8 cM) than for the A and B genomes (1.7 and 2.0 cM, respectively). Seven subpopulations were identified with population structure analysis. A stable QTL was detected for grain yield on chromosome 2DS both under irrigated and rain-fed conditions. A multi-trait region significant for yield and yield components was found on chromosome 5B. Grain yield QTL on chromosome 1BS co-localized with harvest index QTL. Vegetation indices shared QTL with harvest index on chromosome 1AL and 5A. After validation in relevant genetic backgrounds and environments, QTL detected in this study for yield, yield components and drought tolerance-related traits may be used in marker-assisted selection in wheat breeding programs.

Heat and drought adaptive quantitative trait loci (QTL) in a spring bread wheat population resulting from the Seri/Babax cross designed to minimize confounding agronomic traits have been identified previously in trials conducted in Mexico. The same population was grown across a wide range of environments where heat and drought stress are naturally experienced including environments in Mexico, West Asia, North Africa (WANA), and South Asia regions. A molecular genetic linkage map including 475 marker loci associated to 29 linkage groups was used for QTL analysis of yield, days to heading (DH) and to maturity (DM), grain number (GM2), thousand kernel weight (TKW), plant height (PH), canopy temperature at the vegetative and grain filling stages (CTvg and CTgf), and early ground cover. A QTL for yield on chromosome 4A was confirmed across several environments, in subsets of lines with uniform allelic expression of a major phenology QTL, but not independently from PH. With terminal stress, TKW QTL was linked or pleiotropic to DH and DM. The link between phenology and TKW suggested that early maturity would favor the post-anthesis grain growth periods resulting in increased grain size and yields under terminal stress. GM2 and TKW were partially associated with markers at different positions suggesting different genetic regulation and room for improvement of both traits. Prediction accuracy of yield was improved by 5 % when using marker scores of component traits (GM2 and DH) together with yield in multiple regression. This procedure may provide accumulation of more favorable alleles during selection.

Genetic progress in yield will increase if more traits conferring better agronomic and physiological performance are brought together in the same variety through full exploitation of genotyping and phenotyping techniques in breeding. A set of 288 spring wheat advanced lines was tested in different countries in North Africa, Western and South Asia, as well as in Mexico (total of 12 environments) to: identify high yielding germplasm adapted to the former regions; identify sources of variation for physiological traits; and test the ability of physiological traits to predict yield. A group of high yielding advanced lines has been selected in these environments, but significant genotype by environment interactions were observed and were significantly explained (21% of yield variation) by soil pH and air temperature. Associations between traits were dependent on the environment, specifically TKW was positively associated with yield in almost all environments however in Sudan, negative associations were observed. In contrast cooler CT was consistently associated with yield and the trait showed moderate heritability. Agronomic and physiological variables were able to predict 27% of yield variation across advanced lines ( R 2 % by ridge regression) using means of all environments and this model became more significant under stress environments (explaining around 34% of yield variation). Results suggested that if drought and heat adaptive traits are brought together in one genotype, yields can be further increased particularly in low yielding environments.

It has been shown previously that under drought, synthetic hexaploid derived wheat (Triticum aestivum L.) lines outperformed recurrent parents in part due to increased root mass at depth and better water extraction capacity. A group of four elite synthetic derived (SYN-DER) lines and parents was grown under full irrigation and drought conditions to dissect some of the physiological features conferring tolerance to drought. Synthetic derived wheat lines showed on average a 26% yield increase as compared to the parental hexaploid wheats under terminal drought. Different strategies for drought tolerance were observed, including earliness to fl owering, greater root mass at depth, greater water extraction capacity, and increased water use effi ciency (WUE) at anthesis. Some degree of independence was identifi ed between these traits when comparing SYN-DER lines suggesting that these traits are regulated by different genes. The elite SYN-DER line ‘Vorobey’ was an important source of improved root mass at depth under drought. We conclude that the use of wild species of wheat has the potential to improve a range of stress-adaptive traits and may permit modern bread wheat to become adapted to a wider range of environments including climate change scenarios.

Adaptation to abiotic stresses is a quantitative trait controlled by many different genes. Enhancing the tolerance of crop plants to abiotic stresses such as drought has therefore proved to be somewhat elusive in terms of plant breeding. While many C(4) species have significant agronomic importance, most of the research effort on improving drought tolerance has focused on maize. Ideally, drought tolerance has to be achieved without penalties in yield potential. Possibilities for success in this regard are highlighted by studies on maize hybrids performed over the last 70 years that have demonstrated that yield potential and enhanced stress tolerance are associated traits. However, while our understanding of the molecular mechanisms that enable plants to tolerate drought has increased considerably in recent years, there have been relatively few applications of DNA marker technologies in practical C(4) breeding programmes for improved stress tolerance. Moreover, until recently, targeted approaches to drought tolerance have concentrated largely on shoot parameters, particularly those associated with photosynthesis and stay green phenotypes, rather than on root traits such as soil moisture capture for transpiration, root architecture, and improvement of effective use of water. These root traits are now increasingly considered as important targets for yield improvement in C(4) plants under drought stress. Similarly, the molecular mechanisms underpinning heterosis have considerable potential for exploitation in enhancing drought stress tolerance. While current evidence points to the crucial importance of root traits in drought tolerance in C(4) plants, shoot traits may also be important in maintaining high yields during drought.

The responses of C(3) plants to rising atmospheric CO(2) levels are considered to be largely dependent on effects exerted through altered photosynthesis. In contrast, the nature of the responses of C(4) plants to high CO(2) remains controversial because of the absence of CO(2) -dependent effects on photosynthesis. In this study, the effects of atmospheric CO(2) availability on the transcriptome, proteome and metabolome profiles of two ranks of source leaves in maize (Zea mays L.) were studied in plants grown under ambient CO(2) conditions (350 +/- 20 µL L(-1) CO(2) ) or with CO(2) enrichment (700 +/- 20 µL L(-1) CO(2) ). Growth at high CO(2) had no effect on photosynthesis, photorespiration, leaf C/N ratios or anthocyanin contents. However, leaf transpiration rates, carbohydrate metabolism and protein carbonyl accumulation were altered at high CO(2) in a leaf-rank specific manner. Although no significant CO(2) -dependent changes in the leaf transcriptome were observed, qPCR analysis revealed that the abundance of transcripts encoding a Bowman-Birk protease inhibitor and a serpin were changed by the growth CO(2) level in a leaf rank specific manner. Moreover, CO(2) -dependent changes in the leaf proteome were most evident in the oldest source leaves. Small changes in water status may be responsible for the observed responses to high CO(2,) particularly in the older leaf ranks.

Climate change has generated unpredictability in the timing and amount of rain, as well as extreme heat and cold spells that have affected grain yields worldwide and threaten food security. Sources of specific adaptation related to drought and heat, as well as associated breeding of genetic traits, will contribute to maintaining grain yields in dry and warm years. Increased crop photosynthesis and biomass have been achieved particularly through disease resistance and healthy leaves. Similarly, sources of drought and heat adaptation through extended photosynthesis and increased biomass would also greatly benefit crop improvement. Wheat landraces have been cultivated for thousands of years under the most extreme environmental conditions. They have also been cultivated in lower input farming systems for which adaptation traits, particularly those that increase the duration of photosynthesis, have been conserved. Landraces are a valuable source of genetic diversity and specific adaptation to local environmental conditions according to their place of origin. Evidence supports the hypothesis that landraces can provide sources of increased biomass and thousand kernel weight, both important traits for adaptation to tolerate drought and heat. Evaluation of wheat landraces stored in gene banks with highly beneficial untapped diversity and sources of stress adaptation, once characterized, should also be used for wheat improvement. Unified development of databases and promotion of data sharing among physiologists, pathologists, wheat quality scientists, national programmes, and breeders will greatly benefit wheat improvement for adaptation to climate change worldwide.

Water stress and nitrogen (N) availability are the main constraints limiting yield in durum wheat (Triticum turgidum L. var. durum). This work investigates the combined effects of N source (ammonium–NH4+, nitrate–NO3– or a mixture of both–NH4+:NO3–) and water availability (well-watered vs. moderate water stress) on photosynthesis and water-use efficiency in durum wheat (cv. Korifla) flag leaves grown under controlled conditions, using gas exchange, chlorophyll fluorescence and stable carbon isotope composition (δ13C). Under well-watered conditions, NH4+-grown plants had lower net assimilation rates (A) than those grown with the other two N forms. This effect was mainly due to lower stomatal conductance (gs). Under moderate water stress, differences among N forms were not significant, because water regime (WR) had a stronger effect on gs and A than did N source. Consistent with lower gs, δ13C and transpiration efficiency (TE) were the highest in NH4+ leaves in both water treatments. These results indicate higher water-use efficiency in plants fertilized with NH4+ due to stomatal limitation on photosynthesis. Moreover, leaf δ13C is an adequate trait to assess differences in photosynthetic activity and water-use efficiency caused by different N sources. Further, the effect of these growing conditions on the nitrogen isotope composition (δ15N) of flag leaves and roots was examined. Water stress increased leaf δ15N in all N forms. In addition, leaf δ15N increased as root N decreased and as leaf δ13C became less negative. Regardless of WR, the leaf δ15N of NO3–-grown plants was lowest. Based on stepwise and canonical discriminant analyses, we conclude that plant δ15N together with δ13C and other variables may reflect the conditions of N nutrition and water availability where the plants were grown. Thus well-watered plants grown with NH4+:NO3– resembled those grown with NO3–, whereas under water stress they were closer to plants grown with NH4+.

Identification of earliness per se (Eps) flowering time loci in spring wheat are troublesome due to confounding effects of vernalization and photoperiod responses. The Wheat Association Mapping Initiative panel of 287 elite lines was assessed to identify genomic regions associated with Eps and to understand the effects of vernalization and photoperiod treatments in spring wheat. The panel was grown under field conditions with four different treatments: (i) vernalization, where 1-d germinated seeds were kept at 4°C for 6 to 8 wk; (ii) extended photoperiod treatment, from seedling emergence to 10 d after anthesis in the field; (iii) treatments (i) and (ii) in combination; and (iv) a control treatment without either (i) or (ii). The combined vernalization and photoperiod treatments had the greatest effect in advancing the flowering time (4 d). Genome-wide association study in this panel on treatment (iii) detected a locus for Eps in chromosome 1D at 163 to 167 cM. An analysis of the flowering time data on this panel from 19 international environments did not show the presence of Eps in chromosome 1D, indicating the possible masking effect of vernalization and photoperiod genes. This study also validated the diagnostic marker—a transcription factor in the circadian clock input pathway called Triticum aestivum EARLY FLOWERING 3—that is associated with Eps in chromosome 1D and can be used for marker-assisted selection.

This chapter reviews the state-of-the-art and current concepts regarding plant responses to elevated CO2, particularly in terms of whole-plant morphology, molecular physiology and development. It is generally accepted that high temperatures have a severe negative effect on grain quality, and this will probably be exacerbated by elevated CO2 levels. The predicted increases in the temperature of the earth, together with the increased likelihood of heat stress, may serve to reverse the positive effects of elevated CO2 on photosynthesis and plant growth, particularly in C3 species. Plant breeding strategies must therefore incorporate marker-assisted selection with genes that confer improved thermo-tolerance in order to address the growing problem of heat stress and its likely negative impacts on food security and grain quality.

The mobilization of nitrogen (N) compounds and the roles played by glumes and the flag leaf during grain filling were studied in bread wheat (Triticum aestivum L. cv. Florida) grown under field conditions. Glumes lost twice as much of their total N content as that lost by the flag leaf between the milk and early dough stages. In the flag leaf, glumes and grains, Glu, Asp, Ser and Ala accounted for 85% of all the reductions in the free amino acid pool. Principal component analysis of free amino acid pools separated grains from the glumes and the flag leaf, suggesting grain specific regulations in the use of free amino acids in protein synthesis. In all three organs, no decrease in Gln was detected, probably due to steady glutamine synthetase (GS; EC 6.3.1.2) activities per soluble protein in both the flag leaf and glumes. Compared with the flag leaf, glumes presented relatively smaller amounts of the chloroplast GS associated isoform. This we show is due to a lower relative number of mesophyll cells in glumes as supported by the different anatomy and the cellular pattern of the GS immunolocalization. We argue that cellular distribution plays a key role in supporting metabolism to enable the various functions undertaken by glume tissue.

Dehydration avoidance through cooler canopy temperature (CT) has been shown to explain over 60% yield variation in a random progeny derived from a Seri/Babax cross. A near ‘isomorphic’ subset of Seri/Babax progeny and parents encompassing a restricted range of height and phenology were used for detailed characterisation of drought-adaptive trait expression under contrasting water regimes. Under drought, five of the six progeny out yielded the best parent Babax by up to 35%. The main physiological attributes associated with drought adaptation were increased root dry weight at depth, transpiration rate – evidenced by grain carbon isotope discrimination (Δ13C) – grain filling duration and decreased CT during grain filling. Furthermore, increased root mass at depth was associated with reduced levels of stem water soluble carbohydrates (WSC) when comparing genotypes. It is concluded that differences in rooting depth expressed among iso-morphic wheat sister lines explains superior adaptation to drought. These effects can be detected in season using remote sensing. In addition, the data suggest that accumulation of stem carbohydrates and deep rooting may be two alternative strategies for adapting to drought stress, the latter being beneficial where water is available at depth.

Water stress and nitrogen (N) availability are the main constraints on barley (Hordeum vulgare L.) yield in Mediterranean conditions. Here we studied the combined effects of N source and water regime (WR) on plant growth, photosynthesis and carbon isotope discrimination (Δ13C) in barley grown under controlled conditions. The effects of these conditions on plant N isotope discrimination against the fertiliser (Δ15N) was also examined to assess whether the natural variation in plant N isotope composition is a reliable indicator of N nutrition. Six experimental treatments were established with three nutrient solutions containing ammonium (NH4+), nitrate (NO3–) or a mixture of the two (NH4+ : NO3–), each either well watered or moderately water stressed. The NH4+ : NO3– treatment resulted in the greatest biomass accumulation and photosynthetic capacity in both WRs. The NH4+ plants showed accelerated phenology and depressed growth. They also had the lowest photosynthetic rates in both WRs. This effect was mainly due to stomatal closure, while electron transport and carboxylation capacity of leaves were less affected. Consistent with lower stomatal conductance, leaf Δ13C was lower in plants that received NH4+, indicating higher water use efficiency (WUE) not only when irrigated, but also under water stress. In addition, leaf Δ13C and photosynthetic N use efficiency (PNUE) correlated positively with each other and with shoot biomass in both WRs. However, NO3– treatment produced the greatest Δ15N, which was higher in leaves than in roots. Leaf Δ15N was decreased by water stress only in plants in the NO3– treatment. We conclude that leaf Δ13C is an adequate trait to assess the differences in growth, photosynthetic activity and WUE caused by distinct N sources. However, the usefulness of natural abundance of 15N in plant tissue as a nitrogen source marker is restricted by the effect of WR and internal plant fractionation, at least for plants that received NO3–.