Association mapping of leaf rust response in durum wheat

Resistance to leaf rust (Puccinia triticina Eriks.) is a main objective for durum wheat (Triticum durum Desf.) breeding. Association mapping on germplasm collections is now being used as an additional approach for the discovery and validation of major genes/QTLs. In this study, a collection of 164 elite durum wheat accessions suitable for association mapping has been tested for leaf rust response at the seedling stage and under field conditions (adult plant stage). Seedling tests were carried out with 25 selected isolates from durum wheat, bread wheat and triticale, while field experiments were carried out in artificially inoculated plots in Italy and in Mexico. The collection has been profiled with 225 simple sequence repeat (SSR) loci of known map position and a PCR assay targeting Ppd-A1. Associations showing highly consistent experiment-wise significances across leaf rust isolates and field trials were mainly detected for the 7BL distal chromosome (chr.) region (harbouring Lr14 from cultivar Llareta INIA and QLr.ubo-7B.2 from cultivar Creso) and for two chr. regions located in chrs. 2A and 2B. Additionally, isolate-specific associations and/or associations with smaller effects in the field trials were identified in most of the chromosomes. The chr. 7BL distal region was investigated in detail through haplotyping with 15 SSR markers, revealing that the Creso and Llareta INIA alleles are identical by descent at 6 adjacent SSR loci in the most distal 7BL region spanning 8 cM. Association mapping allowed us to further refine the map location of the Lr14/QLr.ubo-7B.2 resistance gene to the most distal region of the linkage group, tagged by Xcfa2257.2, Xgwm344.2 and Xwmc10. The resistant haplotype is present in a number of accessions (ca. 15% of the accessions included in the collection) from the Italian, CIMMYT and ICARDA breeding programmes. Therefore, this chr. 7BL region can be considered as the most important source of resistance to leaf rust currently exploited by durum breeders in the Mediterranean areas. Furthermore, the field trials at the adult plant stage allowed us to identify marker associations (e.g. chrs. 2BL and 3BS, proximal regions; chr. 7BS, distal region) which suggest the presence of minor QTLs for slow-rusting resistance.     

Quantitative genetic analysis and mapping of leaf angle in durum wheat

The leaf erectness profile has been used to optimize plant architecture since erect leaves can enhance photosynthesis and dry matter production by greater sunlight capture. Brassinosteroid is a recent class of phytohormones that has been related to a more erect profile. There are no reports in the literature of the genetic variability of leaf angle in doubled haploid durum wheat populations; most studies on leaf angle have focused on the inheritance. Our aim was to study the genetic variation in flag and penultimate leaf angle in a durum wheat doubled haploid mapping population, identifying and mapping quantitative trait loci influencing leaf angle. An F₁-derived doubled haploid population of 89 lines from the cross Strongfield/Blackbird was used to construct a genetic map using 423 molecular marker loci. Two greenhouse experiments and one field test were conducted using an alpha lattice in a randomized complete block design with three replicates. The leaf angle was measured on flag and penultimate leaf with a protractor at three different growth stages. The results indicated poor to moderate correlations between the position of the leaf angle and the growth stage. Transgressive segregation beyond Strongfield and Blackbird of leaf angle was observed for all environments. Putative trait loci were identified on chromosomes 2A, 2B, 3A, 3B, 4B, 5B and 7A. This work helps to understand the genetics of leaf angle in durum wheat.     

The hormonal control of wheat leaf unrolling

Summary The unrolling of etiolated wheat leaf sections in the dark is stimulated by the application of gibberellic acid (GA₃). GA₃ is most effective if applied for a short time at the beginning of incubation. Kinetin also stimulated leaf unrolling in the dark. AMO1618 and CCC inhibit red light and kinetin-stimulated unrolling. Gibberellin-like substances extracted from red light-treated leaf tissue are effective in stimulating leaf unrolling.Ethylene production in leaf sections is stimulated by IAA, GA₃ and kinetin and inhibited by ABA. A brief exposure to red light decreases the ability of the tissue to produce ethylene. It is concluded that ethylene plays no important role in the control of leaf unrolling by red light or by the application of hormones.Holder of a Science Research Council Studentship.     

QTL mapping of Fusarium head blight resistance in three related durum wheat populations

Key message

The QTL Fhb1 was successfully introgressed and validated in three durum wheat populations. The novel germplasm and the QTL detected will support improvement of Fusarium resistance in durum wheat.

Abstract

Durum wheat (Triticum durum Desf.) is particularly susceptible to Fusarium head blight (FHB) and breeding for resistance is hampered by limited genetic variation within this species. To date, resistant sources are mainly available in a few wild relative tetraploid wheat accessions. In this study, the effect of the well-known hexaploid wheat (Triticum aestivum L.) quantitative trait locus (QTL) Fhb1 was assessed for the first time in durum wheat. Three F7-RIL mapping populations of about 100 lines were developed from crosses between the durum wheat experimental line DBC-480, which carries an Fhb1 introgression from Sumai-3, and the European T. durum cultivars Karur, Durobonus and SZD1029K. The RILs were evaluated in field experiments for FHB resistance in three seasons using spray inoculation and genotyped with SSR as well as genotyping-by-sequencing markers. QTL associated with FHB resistance were identified on chromosome arms 2BL, 3BS, 4AL, 4BS, 5AL and 6AS at which the resistant parent DBC-480 contributed the positive alleles. The QTL on 3BS was detected in all three populations centered at the Fhb1 interval. The Rht-B1 locus governing plant height was found to have a strong effect in modulating FHB severity in all populations. The negative effect of the semi-dwarf allele Rht-B1b on FHB resistance was compensated by combining with Fhb1 and additional resistance QTL. The successful deployment of Fhb1 in T. durum was further substantiated by assessing type 2 resistance in one population. The efficient introgression of Fhb1 represents a significant step forward for enhancing FHB resistance in durum wheat.

     

Molecular mapping of QTL for Fusarium head blight resistance introgressed into durum wheat

Key message

The major QTL for FHB resistance from hexaploid wheat line PI 277012 was successfully introgressed into durum wheat and minor FHB resistance QTL were detected in local durum wheat cultivars. A combination of these QTL will enhance FHB resistance of durum wheat.

Abstract

Fusarium head blight (FHB), caused by Fusarium graminearum, is a devastating disease of durum wheat. To combat the disease, great efforts have been devoted to introgress FHB resistance from its related tetraploid and hexaploid wheat species into adapted durum cultivars. However, most of the quantitative trait loci (QTL) for FHB resistance existing in the introgression lines are not well characterized or validated. In this study, we aimed to identify and map FHB resistance QTL in a population consisting of 205 recombinant inbred lines from the cross between Joppa (a durum wheat cultivar) and 10Ae564 (a durum wheat introgression line with FHB resistance derived from the hexaploid wheat line PI 277012). One QTL (Qfhb.ndwp-2A) from Joppa and two QTL (Qfhb.ndwp-5A and Qfhb.ndwp-7A) from 10Ae564 were identified through phenotyping of the mapping population for FHB severity and DON content in greenhouse and field and genotyping with 90K wheat Infinium iSelect SNP arrays. Qfhb.ndwp-2A explained 14, 15, and 9% of the phenotypic variation, respectively, for FHB severity in two greenhouse experiments and for mean DON content across the two greenhouse environments. Qfhb.ndwp-5A explained 19, 10, and 7% of phenotypic variation, respectively, for FHB severity in one greenhouse experiment, mean FHB severity across two field experiments, and mean DON content across the two greenhouse experiments. Qfhb.ndwp-7A was only detected for FHB severity in the two greenhouse experiments, explaining 9 and 11% of the phenotypic variation, respectively. This study confirms the existence of minor QTL in North Dakota durum cultivars and the successful transfer of the major QTL from PI 277012 into durum wheat.

     

A multiparental cross population for mapping QTL for agronomic traits in durum wheat (Triticum turgidum ssp. durum)

Multiparental cross designs for mapping quantitative trait loci (QTL) provide an efficient alternative to biparental populations because of their broader genetic basis and potentially higher mapping resolution. We describe the development and deployment of a recombinant inbred line (RIL) population in durum wheat (Triticum turgidum ssp. durum) obtained by crossing four elite cultivars. A linkage map spanning 2664 cM and including 7594 single nucleotide polymorphisms (SNPs) was produced by genotyping 338 RILs. QTL analysis was carried out by both interval mapping on founder haplotype probabilities and SNP bi‐allelic tests for heading date and maturity date, plant height and grain yield from four field experiments. Sixteen QTL were identified across environments and detection methods, including two yield QTL on chromosomes 2BL and 7AS, with the former mapped independently from the photoperiod response gene Ppd‐B1, while the latter overlapped with the vernalization locus VRN‐A3. Additionally, 21 QTL with environment‐specific effects were found. Our results indicated a prevalence of environment‐specific QTL with relatively small effect on the control of grain yield. For all traits, functionally different QTL alleles in terms of direction and size of genetic effect were distributed among parents. We showed that QTL results based on founder haplotypes closely matched functional alleles at known heading date loci. Despite the four founders, only 2.1 different functional haplotypes were estimated per QTL, on average. This durum wheat population provides a mapping resource for detailed genetic dissection of agronomic traits in an elite background typical of breeding programmes.     

QTL mapping of resistance to race Ug99 of Puccinia graminis f. sp. tritici in durum wheat (Triticum durum Desf.)

Stem rust caused by Puccinia graminis f. sp. tritici was historically one of the most destructive diseases of wheat worldwide. The evolution and rapid migration of race TTKSK (Ug99) and derivatives, first detected in Uganda in 1999, are of international concern due to the virulence of these races to widely used stem rust resistance genes. In attempts to identify quantitative trait loci (QTL) linked with resistance to stem rust race Ug99, 95 recombinant inbred lines that were developed from a cross between two durum wheat varieties, Kristal and Sebatel, were evaluated for reaction to stem rust. Seven field trials at two locations were carried out in main and off seasons. In addition to the natural infection, the nursery was also artificially inoculated with urediniospores of stem rust race Ug99 and a mixture of locally collected stem rust urediniospores. A genetic map was constructed based on 207 simple sequence repeat (SSR) and two sequence tagged site loci. Using composite interval mapping, nine QTL for resistance to stem rust were identified on chromosomes 1AL, 2AS, 3BS, 4BL, 5BL, 6AL 7A, 7AL and 7BL. These results suggest that durum wheat resistance to stem rust is oligogenic and that there is potential to identify previously uncharacterized resistance genes with minor effects. The SSR markers that are closely linked to the QTL can be used for marker-assisted selection for stem rust resistance in durum wheat.     

Genetic analysis and mapping of adult plant resistance loci to leaf rust in durum wheat cultivar Bairds

Key message

New leaf rust adult plant resistance (APR) QTL QLr.cim - 6BL was mapped and confirmed the known pleotropic APR gene Lr46 effect on leaf rust in durum wheat line Bairds.

Abstract

CIMMYT-derived durum wheat line Bairds displays an adequate level of adult plant resistance (APR) to leaf rust in Mexican field environments. A recombinant inbred line (RIL) population developed from a cross of Bairds with susceptible parent Atred#1 was phenotyped for leaf rust response at Ciudad Obregon, Mexico, during 2013, 2014, 2015 and 2016 under artificially created epidemics of Puccinia triticina (Pt) race BBG/BP. The RIL population and its parents were genotyped with the 50 K diversity arrays technology (DArT) sequence system and simple sequence repeat (SSR) markers. A genetic map comprising 1150 markers was used to map the resistance loci. Four significant quantitative trait loci (QTLs) were detected on chromosomes 1BL, 2BC (centromere region), 5BL and 6BL. These QTLs, named Lr46, QLr.cim-2BC, QLr.cim-5BL and QLr.cim-6BL, respectively, explained 13.5–60.8%, 9.0–14.3%, 2.8–13.9%, and 11.6–29.4%, respectively, of leaf rust severity variation by the inclusive composite interval mapping method. All of these resistance loci were contributed by the resistant parent Bairds, except for QLr.cim-2BC, which came from susceptible parent Atred#1. Among these, the QTL on chromosome 1BL was the known pleiotropic APR gene Lr46, whereas QLr.cim-6BL, a consistently detected locus, should be a new leaf rust resistance locus in durum wheat. The mean leaf rust severity of RILs carrying all four QTLs ranged from 8.0 to 17.5%, whereas it ranged from 10.9 to 38.5% for three QTLs (Lr46 + 5BL + 6BL) derived from the resistant parent Bairds. Two RILs with four QTLs combinations can be used as sources of complex APR in durum wheat breeding.

     

Stay-green trait-antioxidant status interrelationship in durum wheat (Triticum durum) flag leaf during post-flowering

Three independent durum wheat mutant lines that show delayed leaf senescence or stay-green (SG) phenotype, SG196, SG310 and SG504, were compared to the parental genotype, cv. Trinakria, with respect to the photosynthetic parameters and the cellular redox state of the flag leaf in the period from flowering to senescence. The SG mutants maintained their chlorophyll content and net photosynthetic rate for longer than Trinakria, thus revealing a functional SG phenotype. They also showed a better redox state as demonstrated by: (1) a lower rate of superoxide anion production due to generally higher activity of the antioxidant enzymes superoxide dismutase and catalase in all of the SG mutants and also of the total peroxidase in SG196; (2) a higher thiol content that can be ascribed to a higher activity of the NADPH-providing enzyme glucose-6-phosphate dehydrogenase in all of the SG mutants and also of the NADP⁺-dependent malic enzyme in SG196; (3) a lower pro-oxidant activity of lipoxygenase that characterises SG196 and SG504 mutants close to leaf senescence. Overall, these results show a general relationship in durum wheat between the SG phenotype and a better redox state. This relationship differs across the different SG mutants, probably as a consequence of the different set of altered genes underlying the SG trait in these independent mutant lines.     

QTL mapping of resistance to leaf rust in Salix

Genetic mapping of quantitative trait loci (QTL) for resistance to Melampsora leaf rust was performed in two willow families: the progeny from a backcross between Salix viminalis and a hybrid S. viminalis × Salix schwerinii (population S₁), and the F₁ progeny of a cross between two S. viminalis (population S₃). Disease levels were scored in the field for three consecutive years. In the laboratory, five different rust strains were sprayed onto leaf disks and the following resistance components were scored: latent period, diameter and number of uredinia, and flecking. One major QTL and 14 smaller were identified in the S₁ host population. One rust strain, that represents a Melampsora form with limited incidence on S. viminalis, showed lower aggressiveness to the S₁ host population together with a different pattern in QTLs. In the S₃ host population, we detected 13 QTLs for rust resistance, of which two were located to the same genomic regions as those found for the S₁ population. We showed that the strongest QTL co-segregated with a gene homologous to a known Toll/interleukin receptor-nucleotide binding site-leucine-rich repeat resistance gene in poplar. The importance of the identified QTLs is discussed in relation to breeding for durable resistance.     

QTL mapping of adult-plant resistances to stripe rust and leaf rust in Chinese wheat cultivar Bainong 64

Stripe rust and leaf rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss. and P. triticina, respectively, are devastating fungal diseases of common wheat (Triticum aestivum L.). Chinese wheat cultivar Bainong 64 has maintained acceptable adult-plant resistance (APR) to stripe rust, leaf rust and powdery mildew for more than 10?years. The aim of this study was to identify quantitative trait loci/locus (QTL) for resistance to the two rusts in a population of 179 doubled haploid (DH) lines derived from Bainong 64?×?Jingshuang 16. The DH lines were planted in randomized complete blocks with three replicates at four locations. Stripe rust tests were conducted using a mixture of currently prevalent P. striiformis races, and leaf rust tests were performed with P. triticina race THTT. Leaf rust severities were scored two or three times, whereas maximum disease severities (MDS) were recorded for stripe rust. Using bulked segregant analysis (BSA) and simple sequence repeat (SSR) markers, five independent loci for APR to two rusts were detected. The QTL on chromosomes 1BL and 6BS contributed by Bainong 64 conferred resistance to both diseases. The loci identified on chromosomes 7AS and 4DL had minor effects on stripe rust response, whereas another locus, close to the centromere on chromosome 6BS, had a significant effect only on leaf rust response. The loci located on chromosomes 1BL and 4DL also had significant effects on powdery mildew response. These were located at the same positions as the Yr29/Lr46 and Yr46/Lr67 genes, respectively. The multiple disease resistance locus for APR on chromosome 6BS appears to be new. All three genes and their closely linked molecular markers could be used in breeding wheat cultivars with durable resistance to multiple diseases.     

Genetic analysis of durable resistance against leaf rust in durum wheat

The Italian durum wheat cultivar Creso possesses a high level of durable resistance to leaf rust based on both hypersensitive and non-hypersensitive components. In order to investigate the genetic basis of this resistance, a segregating population composed of 123 recombinant inbred lines (RILs) derived from the cross Creso × Pedroso, was evaluated for disease severity in adult plants under field conditions. Furthermore, the resistance of parents and RILs was evaluated by assessing macroscopically the latency period and microscopically the number and type of pathogen colonies formed following artificial inoculation with a specific isolate. This experiment was performed at controlled conditions at two developmental stages. Besides some minor QTLs, one major QTL explaining both reduction of disease severity in the field and increased latency period was found on the long arm of chromosome 7B, and closely associated PCR-based and DArT markers were identified. Daniela Marone and Ana I. Del Olmo contributed equally to the work.     

QTL mapping of resistance to gray leaf spot in ryegrass

Gray leaf spot (GLS) is a serious fungal disease caused by Magnaporthe grisea, recently reported on perennial ryegrass (Lolium perenne L.), an important turfgrass and forage species. This fungus also causes rice blast and many other grass diseases. Rice blast is usually controlled by host resistance, but durability of resistance is a problem. Little GLS resistance has been reported in perennial ryegrass. However, greenhouse inoculations in our lab using one ryegrass isolate and one rice-infecting lab strain suggest presence of partial resistance. A high density linkage map of a three generation Italian × perennial ryegrass mapping population was used to identify quantitative trait loci (QTL) for GLS resistance. Potential QTL of varying effect were detected on four linkage groups, and resistance to the ryegrass isolate and the lab strain appeared to be controlled by different QTL. Of three potential QTL detected using the ryegrass isolate, the one with strongest effect for resistance was located on linkage group 3 of the MFB parent, explaining between 20% and 37% of the phenotypic variance depending on experiment. Another QTL was detected on linkage group 6 of the MFA parent, explaining between 5% and 10% of the phenotypic variance. The two QTL with strongest effect for resistance to the lab strain were located on linkage groups MFA 2 and MFB 4, each explaining about 10% of the phenotypic variance. Further, the QTL on linkage groups 3 and 4 appear syntenic to blast resistance loci in rice. This work will likely benefit users and growers of perennial ryegrass, by setting the stage for improvement of GLS resistance in perennial ryegrass through marker-assisted selection.     

Identification and mapping of leaf, stem and stripe rust resistance quantitative trait loci and their interactions in durum wheat

Leaf rust (Puccinia triticina Eriks.), stripe rust (Puccinia striiformis f. tritici Eriks.) and stem rust (Puccinia graminis f. sp. tritici) cause major production losses in durum wheat (Triticum turgidum L. var. durum). The objective of this research was to identify and map leaf, stripe and stem rust resistance loci from the French cultivar Sachem and Canadian cultivar Strongfield. A doubled haploid population from Sachem/Strongfield and parents were phenotyped for seedling reaction to leaf rust races BBG/BN and BBG/BP and adult plant response was determined in three field rust nurseries near El Batan, Obregon and Toluca, Mexico. Stripe rust response was recorded in 2009 and 2011 nurseries near Toluca and near Njoro, Kenya in 2010. Response to stem rust was recorded in field nurseries near Njoro, Kenya, in 2010 and 2011. Sachem was resistant to leaf, stripe and stem rust. A major leaf rust quantitative trait locus (QTL) was identified on chromosome 7B at Xgwm146 in Sachem. In the same region on 7B, a stripe rust QTL was identified in Strongfield. Leaf and stripe rust QTL around DArT marker wPt3451 were identified on chromosome 1B. On chromosome 2B, a significant leaf rust QTL was detected conferred by Strongfield, and at the same QTL, a Yr gene derived from Sachem conferred resistance. Significant stem rust resistance QTL were detected on chromosome 4B. Consistent interactions among loci for resistance to each rust type across nurseries were detected, especially for leaf rust QTL on 7B. Sachem and Strongfield offer useful sources of rust resistance genes for durum rust breeding.     

Barley leaf unrolling. The proline connection

Unrolling of 1 cm sections, taken between 3 and 4 cm from the apex, of 6-day-old, etiolated barley leaves, was promoted by blue (426 nm) and red (658 nm) light. Accompanying such unrolling was a reduction in the level of the free proline of the tissue. When leaf unrolling was prevented by irradiation with far-red (728 nm) light, or treatment with abscisic acid (ABA) following red light irradiation, the level of proline remained more or less unchanged, at the level of the untreated, dark controls. The proline analogue, azetidine carboxylic acid (AZC) powerfully inhibited the light induced leaf opening, emphasizing the significance of proline-containing, structural and functional proteins in barley leaf unrolling. The inhibition imposed by AZC is partially reversible by added proline.     

Precise mapping of a locus affecting grain protein content in durum wheat

Grain protein content (GPC) is an important factor in pasta and breadmaking quality, and in human nutrition. It is also an important trait for wheat growers because premium prices are frequently paid for wheat with high GPC. A promising source for alleles to increase GPC was detected on chromosome 6B of Triticum turgidum var. dicoccoides accession FA-15-3 (DIC). Two previous quantitative trait locus (QTL) studies found that the positive effect of DIC-6B was associated to a single locus located between the centromere and the Nor-B2 locus on the short arm of chromosome 6B. Microsatellite markers Xgwm508 and Xgwm193 flanking the QTL region were used in this study to develop 20 new homozygous recombinant substitution lines (RSLs) with crossovers between these markers. These 20 RSLs, plus nine RSLs developed in previous studies were characterized with four new RFLP markers located within this chromosome segment. Grain protein content was determined in three field experiments organized as randomized complete block designs with ten replications each. The QTL peaks for protein content were located in the central region of a 2.7-cM interval between RFLP markers Xcdo365 and Xucw67 in the three experiments. Statistical analyses showed that almost all lines could be classified unequivocally within low- and high- protein groups, facilitating the mapping of this trait as a single Mendelian locus designated Gpc-6B1. The Gpc-6B1 locus was mapped 1.5-cM proximal to Xcdo365 and 1.2-cM distal to Xucw67. These new markers can be used to reduce the size of the DIC chromosome segment selected in marker-assisted selection programs. Markers Nor-B2 and Xucw66 flanking the previous two markers can be used to select against the DIC segment and reduce the linkage drag during the transfer of Gpc-6B1 into commercial bread and pasta wheat varieties. The precise mapping of the high GPC gene, the high frequency of recombinants recovered in the targeted region, and the recent development of a tetraploid BAC library including the Gpc-6B1 DIC allele are the first steps towards the map-based cloning of this gene.Communicated by J. Dvorak     

QTL mapping for resistance of maize to grey leaf spot

Grey leaf spot (GLS) is a global maize leaf disease that seriously endangers maize production. Discovering and utilizing genetic loci for GLS resistance would be useful for breeding new varieties with improved resistance. In this study, 233 F_2:3 families (produced from the susceptible inbred line 08‐641 × the resistant inbred line 446) were used for quantitative trait locus (QTL) mapping of resistance to GLS. Five GLS resistance QTLs were detected on chromosomes 1, 2, 3, 4, and 6, which explained 6.7%‐21.3% of the phenotypic variation. The QTLs, qRgls.CH‐4, qRgls.CH‐1, qRgls.CH‐2, and qRgls.CH‐6, were stably expressed in the four environments, and all loci for GLS resistance were derived from the resistant parent, 446. The additive effects of qRgls.CH‐4, qRgls.CH‐1, and qRgls.CH‐6 were significantly greater than their single dominant effects, which may be beneficial for GLS resistance breeding. The QTL qRgls.CH‐6, located in bins 6.02–6.05, did not overlap with any previously reported resistance QTL and thus was identified here for the first time. QTL analysis of PI (leaf performance index) detected three leaf function QTLs on chromosomes 4, 8, and 9 were related to GLS resistance and explained 4.8%‐6.2% of the phenotypic variation. Among them, qPI.CH‐4 was significantly stronger expressed in several environments; this allele associated with increased leaf function came from the resistant parent, 446, and its interval overlapped with that of qRgls.CH‐4. Furthermore, both qRgls.CH‐4 and qPI.CH‐4 were located in a hotspot area for GLS resistance in bins 4.05‐4.06, indicating that GLS resistance was significantly related to leaf performance and that GLS significantly reduced leaf photosynthetic performance.     

Assessing durum wheat ear and leaf metabolomes in the field through hyperspectral data

Hyperspectral techniques are currently used to retrieve information concerning plant biophysical traits, predominantly targeting pigments, water, and nitrogen‐protein contents, structural elements, and the leaf area index. Even so, hyperspectral data could be more extensively exploited to overcome the breeding challenges being faced under global climate change by advancing high‐throughput field phenotyping. In this study, we explore the potential of field spectroscopy to predict the metabolite profiles in flag leaves and ear bracts in durum wheat. The full‐range reflectance spectra (visible (VIS)‐near‐infrared (NIR)‐short wave infrared (SWIR)) of flag leaves, ears and canopies were recorded in a collection of contrasting genotypes grown in four environments under different water regimes. GC‐MS metabolite profiles were analyzed in the flag leaves, ear bracts, glumes, and lemmas. The results from regression models exceeded 50% of the explained variation (adj‐R² in the validation sets) for at least 15 metabolites in each plant organ, whereas their errors were considerably low. The best regressions were obtained for malate (82%), glycerate and serine (63%) in leaves; myo‐inositol (81%) in lemmas; glycolate (80%) in glumes; sucrose in leaves and glumes (68%); γ‐aminobutyric acid (GABA) in leaves and glumes (61% and 71%, respectively); proline and glucose in lemmas (74% and 71%, respectively) and glumes (72% and 69%, respectively). The selection of wavebands in the models and the performance of the models based on canopy and VIS organ spectra and yield prediction are discussed. We feel that this technique will likely to be of interest due to its broad applicability in ecophysiology research, plant breeding programmes, and the agri‐food industry.     

Fine mapping TaFLW1, a major QTL controlling flag leaf width in bread wheat (Triticum aestivum L.)

Introduction

Flag leaf width (FLW) is directly related to photosynthetic capacity and yield potential in wheat. In a previous study, Qflw.nau-5A controlling FLW was detected on chromosome 5A in the interval possessing Fhb5 for type I Fusarium head blight (FHB) resistance using a recombinant inbred line population derived from Nanda2419 × Wangshuibai.

Materials and methods

Qflw.nau-5A near-isogenic line (NIL) with the background of Mianyang 99-323 and PH691 was developed and evaluated. FLW inheritance was investigated using two F₂ populations developed from crossing the Qflw.nau-5A NILs with their recurrent parents. One hundred ten and 28 recombinants, which included 10 and 5 types of recombinants, were identified from 2816 F₂ plants with Mianyang 99-323 background and 1277 F₂ plants with PH691 background, respectively, and phenotyped in field trials for FLW and type I FHB resistance. Deletion bin mapping was applied to physically map Qflw.nau-5A.

Results and conclusions

The introduction of Wangshuibai Qflw.nau-5A allele reduced the FLW up to 3 mm. In the F₂ populations, Qflw.nau-5A was inherited like a semi-dominant gene, and was therefore designated as TaFLW1. The FLW of the recombinant lines displayed a distinct two-peak distribution. Recombinants with wider leaves commonly have Mianyang 99-323 or PH691 chromatin in the 0.2 cM Xwmc492-Xwmc752 interval that resided in the 5AL12-0.35–0.57 deletion bin, and recombinants with narrow leaves were Wangshuibai genotype in this interval. Phenotypic recombination between FLW and type I FHB resistance was identified, implying TaFLW1 was in close linkage with Fhb5. These results should aid wheat breeders to break the linkage drag through marker-assisted selection and assist in the map-based cloning of TaFLW1.