Search

In the present era of climate instability, Canadian wheat production has been frequently affected by abiotic stresses and by dynamic populations of pathogens and pests that are more virulent and aggressive over time. Genetic diversity is fundamental to guarantee sustainable and improved wheat production. In the past, the genetics of Brazilian cultivars, such as Frontana, have been studied by Canadian researchers and consequently, Brazilian germplasm has been used to breed Canadian wheat cultivars. The objective of this study was to characterize a collection of Brazilian germplasm under Canadian growing conditions, including the reaction of the Brazilian germplasm to Canadian isolates/pathogens and to predict the presence of certain genes in an effort to increase genetic diversity, improve genetic gain and resilience of Canadian wheat. Over 100 Brazilian hard red spring wheat cultivars released from 1986 to 2016 were evaluated for their agronomic performance in eastern Canada. Some cultivars showed good adaptability, with several cultivars being superior or statistically equal to the highest yielding Canadian checks. Several Brazilian cultivars had excellent resistance to leaf rust, even though only a few of these tested positive for the presence of either Lr34 or Lr16, two of the most common resistance genes in Canadian wheat. Resistance for stem rust, stripe rust and powdery mildew was variable among the Brazilian cultivars. However, many Brazilian cultivars had high levels of resistance to Canadian and African - Ug99 strains of stem rust. Many Brazilian cultivars had good Fusarium head blight (FHB) resistance, which appears to be derived from Frontana. In contrast FHB resistance in Canadian wheat is largely based on the Chinese variety, Sumai-3. The Brazilian germplasm is a valuable source of semi-dwarf (Rht) genes, and 75% of the Brazilian collection possessed Rht-B1b. Many cultivars in the Brazilian collection were found to be genetically distinct from Canadian wheat, making them a valuable resource to increase the disease resistance and genetic variability in Canada and elsewhere.

Abstract Background Treatment of wheat with the phytohormones abscisic acid (ABA) and gibberellic acid (GA) has been shown to affect Fusarium head blight (FHB) disease severity. However, the molecular mechanisms underlying the elicited phenotypes remain unclear. Toward addressing this gap in our knowledge, global transcriptomic profiling was applied to the FHB-susceptible wheat cultivar ‘Fielder’ to map the regulatory responses effected upon treatment with ABA, an ABA receptor antagonist (AS6), or GA in the presence or absence of Fusarium graminearum (Fg) challenge. Results Spike treatments resulted in a total of 30,876 differentially expressed genes (DEGs) identified in ‘Fielder’ (26,004) and the Fg (4872) pathogen. Topology overlap and correlation analyses defined 9689 wheat DEGs as Fg-related across the treatments. Further enrichment analyses demonstrated that these included expression changes within ‘Fielder’ defense responses, cell structural metabolism, molecular transport, and membrane/lipid metabolism. Dysregulation of ABA and GA crosstalk arising from repression of ‘Fielder’ FUS3 was noted. As well, expression of a putative Fg ABA-biosynthetic cytochrome P450 was detected. The co-applied condition of Fg + ABA elicited further up-regulation of phytohormone biosynthesis, as well as SA and ET signaling pathways and cell wall/polyphenolic metabolism. In contrast, co-applied Fg + GA mainly suppressed phytohormone biosynthesis and signaling, while modulating primary and secondary metabolism and flowering. Unexpectedly, co-applied Fg + AS6 did not affect ABA biosynthesis or signaling, but rather elicited antagonistic responses tied to stress, phytohormone transport, and FHB disease-related genes. Conclusions Observed exacerbation (misregulation) of classical defense mechanisms and cell wall fortifications upon ABA treatment are consistent with its ability to promote FHB severity and its proposed role as a fungal effector. In contrast, GA was found to modulate primary and secondary metabolism, suggesting a general metabolic shift underlying its reduction in FHB severity. While AS6 did not antagonize traditional ABA pathways, its impact on host defense and Fg responses imply potential for future investigation. Overall, by comparing these findings to those previously reported for four additional plant genotypes, an additive model of the wheat-Fg interaction is proposed in the context of phytohormone responses.

TaNAM transcription factors play an important role in controlling senescence, which in turn, influences the delivery of nitrogen, iron and other elements to the grain of wheat (Triticum aestivum) plants, thus contributing to grain nutritional value. While lack or diminished expression of TaNAMs determines a stay-green phenotype, the precise effect of these factors on chloroplast structure has not been studied. In this work we focused on the events undergone by chloroplasts in two wheat lines having either control or diminished TaNAM expression due to RNA interference (RNAi). It was found that in RNAi plants maintenance of chlorophyll levels and maximal photochemical efficiency of photosystem II were associated with lack of chloroplast dismantling. Flow cytometer studies and electron microscope analysis showed that RNAi plants conserved organelle ultrastructure and complexity. It was also found that senescence in control plants was accompanied by a low leaf enzymatic antioxidant activity. Lack of chloroplast dismantling in RNAi plants was associated with maintenance of protein and iron concentration in the flag leaf, the opposite being observed in control plants. These data provide a structural basis for the observation that down regulation of TaNAMs confers a functional stay-green phenotype and indicate that the low export of iron and nitrogen from the flag leaf of these plants is concomitant, within the developmental window studied, with lack of chloroplast degradation and high enzymatic antioxidant activity.

Genetic susceptibility to late maturity alpha-amylase (LMA) in wheat (Triticum aestivum L.) results in increased alpha-amylase activity in mature grain when cool conditions occur during late grain maturation. Farmers are forced to sell wheat grain with elevated alpha-amylase at a discount because it has an increased risk of poor end-product quality. This problem can result from either LMA or preharvest sprouting, grain germination on the mother plant when rain occurs before harvest. Whereas preharvest sprouting is a well-understood problem, little is known about the risk LMA poses to North American wheat crops. To examine this, LMA susceptibility was characterized in a panel of 251 North American hard spring wheat lines, representing ten geographical areas. It appears that there is substantial LMA susceptibility in North American wheat since only 27% of the lines showed reproducible LMA resistance following cold-induction experiments. A preliminary genome-wide association study detected six significant marker-trait associations. LMA in North American wheat may result from genetic mechanisms similar to those previously observed in Australian and International Maize and Wheat Improvement Center (CIMMYT) germplasm since two of the detected QTLs, QLMA.wsu.7B and QLMA.wsu.6B, co-localized with previously reported loci. The Reduced height (Rht) loci also influenced LMA. Elevated alpha-amylase levels were significantly associated with the presence of both wild-type and tall height, rht-B1a and rht-D1a, loci in both cold-treated and untreated samples. [ABSTRACT FROM AUTHOR]

Abiotic stress tolerance in plants is pivotal to increase yield stability, but its genetic basis is still poorly understood. To gain insight into the genetic architecture of frost tolerance, this work evaluated a large mapping population of 1739 wheat (Triticum aestivum L.) lines and hybrids adapted to Central Europe in field trials in Germany and fingerprinted the lines with a 9000 single-nucleotide polymorphism array. Additive effects prevailed over dominance effects. A two-dimensional genome scan revealed the presence of epistatic effects. Genome-wide association mapping in combination with a robust cross-validation strategy identified one frost tolerance locus with a major effect located on chromosome 5B. This locus was not in linkage disequilibrium with the known frost loci Fr-B1 and Fr-B2. The use of the detected diagnostic markers on chromosome 5B, however, does not allow prediction of frost tolerance with high accuracy. Application of genome-wide selection approaches that take into account also loci with small effect sizes considerably improved prediction of the genetic variation of frost tolerance in wheat. The developed prediction model is valuable for improving frost tolerance because this trait displays a wide variation in occurrence across years and is therefore a difficult target for conventional phenotypic selection.

Stem rust caused by Puccinia graminis f. sp. tritici (Pgt) remains a constraint to wheat production in East Africa. In this study, we characterized the genetics of stem rust resistance, identified QTLs, and described markers associated with stem rust resistance in the spring wheat line CI 14275. The 113 recombinant inbred lines, together with their parents, were evaluated at the seedling stage against Pgt races TTKSK, TRTTF, TPMKC, TTTTF, and RTQQC. Screening for resistance to Pgt races in the field was undertaken in Kenya, Ethiopia, and the United States in 2016, 2017, and 2018. One gene conferred seedling resistance to race TTTTF, likely Sr7a. Three QTL were identified that conferred field resistance. QTL QSr.cdl-2BS.2 , that conferred resistance in Kenya and Ethiopia, was validated, and the marker Excalibur_c7963_1722 was shown to have potential to select for this QTL in marker-assisted selection. The QTL QSr.cdl-3B.2 is likely Sr12 , and QSr.cdl-6A appears to be a new QTL. This is the first study to both detect and validate an adult plant stem rust resistance QTL on chromosome arm 2BS. The combination of field QTL QSr.cdl-2BS.2 , QSr.cdl-3B.2 , and QSr.cdl-6A has the potential to be used in wheat breeding to improve stem rust resistance of wheat varieties. [ABSTRACT FROM AUTHOR]

The mechanisms of aluminum (Al) resistance in wheat and rye involve the release of citrate and malate anions from the root apices. Many of the genes controlling these processes have been identified and their responses to Al treatment described in detail. This study investigated how the major Al resistance traits of wheat and rye are transferred to triticale (x Tritosecale Wittmack) which is a hybrid between wheat and rye. We generated octoploid and hexaploid triticale lines and compared them with the parental lines for their relative resistance to Al, organic anion efflux and expression of some of the genes encoding the transporters involved. We report that the strong Al resistance of rye was incompletely transferred to octoploid and hexaploid triticale. The wheat and rye parents contributed to the Al-resistance of octoploid triticale but the phenotypes were not additive. The Al resistance genes of hexaploid wheat, TaALMT1 , and TaMATE1B , were more successfully expressed in octoploid triticale than the Al resistance genes in rye tested, ScALMT1 and ScFRDL2. This study demonstrates that an important stress-tolerance trait derived from hexaploid wheat was expressed in octoploid triticale. Since most commercial triticale lines are largely hexaploid types it would be beneficial to develop techniques to generate genetically-stable octoploid triticale material. This would enable other useful traits that are present in hexaploid but not tetraploid wheat, to be transferred to triticale. [ABSTRACT FROM AUTHOR]

Abstract Currently, food security depends on the increased production of cereals such as wheat (Triticum aestivum L.), which is an important source of calories and protein for humans. However, cells of the crop have suffered from the accumulation of reactive oxygen species (ROS), which can cause severe oxidative damage to the plants, due to environmental stresses. ROS are toxic molecules found in various subcellular compartments. The equilibrium between the production and detoxification of ROS is sustained by enzymatic and nonenzymatic antioxidants. In the present review, we offer a brief summary of antioxidant defense and hydrogen peroxide (H2O2) signaling in wheat plants. Wheat plants increase antioxidant defense mechanisms under abiotic stresses, such as drought, cold, heat, salinity and UV-B radiation, to alleviate oxidative damage. Moreover, H2O2 signaling is an important factor contributing to stress tolerance in cereals.

Background: Phytoene synthase 1 (PSY1) is the most important regulatory enzyme in carotenoid biosynthesis, whereas its function is hardly known in common wheat. The aims of the present study were to investigate Psy1 function and genetic regulation using reverse genetics approaches. Results: Transcript levels of Psy1 in RNAi transgenic lines were decreased by 54-76 % and yellow pigment content (YPC) was reduced by 26-35 % compared with controls, confirming the impact of Psy1 on carotenoid accumulation. A series of candidate genes involved in secondary metabolic pathways and core metabolic processes responded to Psy1 down-regulation. The aspartate rich domain (DXXXD) was important for PSY1 function, and conserved nucleotides adjacent to the domain influenced YPC by regulating gene expression, enzyme activity or alternative splicing. Compensatory responses analysis indicated that three Psy1 homoeologs may be coordinately regulated under normal conditions, but separately regulated under stress. The period 14 days post anthesis (DPA) was found to be a key regulation node during grain development. Conclusion: The findings define key aspects of flour color regulation in wheat and facilitate the genetic improvement of wheat quality targeting color/nutritional specifications required for specific end products. [ABSTRACT FROM AUTHOR]

Stem rust in wheat remained under control for several decades all over the earth by the mid-1990's resulting in less emphasis on breeding for resistance to this disease and had not been priority in research for considerable era. The manifestation and expansion of races of Puccinia graminis f. sp. tritici commonly known as Ug99 with virulence for the Sr31 resistance gene in 1998 in Uganda renewed interest in breeding for resistance to stem rust of wheat. Wheat community responded instantaneously. Global Ug99 stem rust screening services were launched in 2005 under the shade of Borlaug Global Rust Initiative (BGRI) in Kenya and Ethiopia with purpose to recognize auxiliary sources of resistance. Screening in Kenya and Ethiopia of wheat materials from Asian countries carried out in 2005-06 disclosed a very low frequency of lines resistant to Ug99 and its variants. Considerable achievements have been attained identifying diverse race-specific resistance and adult plant resistance (APR) genes that can be exploited to improve wheat germplasm to contest the hazard. Four more genes namely Sr55, Sr56, Sr57 and Sr58 along with the Sr2 gene, now have been characterized to confer slow rusting. New perspectives on rust control in the future through the development of multiple resistance gene cassettes through cloning of some rust resistance genes opens. The strain spread to eastern and southern Africa and in Iran. Meanwhile evolution has also been observed in the strain generating new variants. Currently, 10 variants in the Ug99 race group have been perceived in twelve countries. SAARC wheat disease trap nursery has been developed in the vicinity of Iran where Ug99 was perceived in 2007. Data designates that Pgt-Ug99 (TTKSK) reported from Iran in 2007 has not evolved further, nor has it extended to adjacent Pakistan or India to impose any crop failure. [ABSTRACT FROM AUTHOR]

The bread wheat line WR95 showed seedling resistance to several Indian stem rust ( Puccinia graminis Pers. f. sp. tritici) isolates. Genetic analysis of stem rust resistance in WR95 was undertaken in populations derived from crosses NI5439/WR95 and Agra Local/WR95. The F, F, and F generations derived from the cross NI5439/WR95 were tested against stem rust isolate 40A and genetic analysis showed a recessive gene for resistance. The results were confirmed in another F population derived from the cross Agra Local/WR95. Interestingly, genetic analysis in F population from the later cross i.e. Agra Local/WR95 identified a dominant gene against isolates 11 and 11A. The recessive gene against isolate 40A was mapped to the long arm of 5D chromosome. WR95 showed resistance to virulent isolates of Sr30 which is also located on 5DL chromosome. The dominant gene in WR95 that conferred the resistance to isolate 11 and 11A was mapped towards telomeric region of the long arm of 2B chromosome. The long arm of chromosome 2B also carries stem rust resistance genes Sr9, Sr16 and Sr28. WR95 showed resistance to virulent isolates to Sr9b (11, 11A, 21A-2 and 40A), Sr9e (15-1 and 40A) and Sr28 (11, 11A, 15-1, 21A-2 and 40A). The map position of dominant gene identified in WR95 is different from Sr9 and Sr28 while Sr16 is towards telomeric region and not mapped so far. Therefore, the dominant gene in WR95 may be either Sr16 or a new gene. [ABSTRACT FROM AUTHOR]

Wheat ( Triticum aestivum L.) powdery mildew has direct effects on photosynthesis- and energy-related pathways. Because it is prevalent in Sichuan Province, China, knowledge concerning Pm40 -mediated wheat powdery mildew resistance is important for understanding host–pathogen interactions. The aim of this study was to understand physiological changes during the host–pathogen interaction, including gene expression, photosynthetic and chlorophyll fluorescence parameters, chlorophyll content, and antioxidant activity, specific to the resistance response to powdery mildew. The Pm40- expressing L693 and Pm40 -deficient L1095 wheat lines were employed for comparison analyses. Fifty-eight and 26 expressed sequence tags (ESTs) were obtained from forward and reverse suppression subtractive hybridization cDNA libraries constructed from Bgt -infected L693 and L1095 leaves, respectively, and 69% of the ESTs in the forward library were related to photosynthesis- and energy metabolism-related pathways. Our data indicate that photosynthesis and carbon metabolism as well as nitrogen metabolism related to photosynthesis are the main pathways involved in Pm40 -mediated wheat powdery mildew resistance and that an acetyl CoA-like gene might be a key regulatory factor in these pathways. This study provides new insight into the physiological and genetic mechanisms of resistance to wheat powdery mildew. [ABSTRACT FROM AUTHOR]

Stay-green plants retain green leaves longer after anthesis and can have improved yield, particularly under water limitation. As senescence is a dynamic process, genotypes with different senescence patterns may exhibit similar final normalised difference vegetative index (NDVI). By monitoring NDVI from as early as awn emergence to maturity, we demonstrate that analysing senescence dynamics improves insight into genotypic stay-green variation. A senescence evaluation tool was developed to fit a logistic function to NDVI data and used to analyse data from three environments for a wheat (Triticum aestivum L.) population whose lines contrast for stay-green. Key stay-green traits were estimated including, maximum NDVI, senescence rate and a trait integrating NDVI variation after anthesis, as well as the timing from anthesis to onset, midpoint and conclusion of senescence. The integrative trait and the timing to onset and mid-senescence exhibited high positive correlations with yield and a high heritability in the three studied environments. Senescence rate was correlated with yield in some environments, whereas maximum NDVI was associated with yield in a drought-stressed environment. Where resources preclude frequent measurements, we found that NDVI measurements may be restricted to the period of rapid senescence, but caution is required when dealing with lines of different phenology. In contrast, regular monitoring during the whole period after flowering allows the estimation of senescence dynamics traits that may be reliably compared across genotypes and environments. We anticipate that selection for stay-green traits will enhance genetic progress towards high-yielding, stay-green germplasm. [ABSTRACT FROM AUTHOR]

A deep and thick root system has a positive effect on wheat yield, particularly in drought environments. A doubled haploid (DH) population of 150 lines derived from the cross Hanxuan 10 × Lumai 14 was used to map QTLs for seedling root characteristics. The DH lines were cultivated in an agarose gel-chamber under well-watered (WW) and water-stressed (WS) regimes. Water stress was simulated by adding mannitol to the agarose gel. The seminal root traits, including maximum root length (MRL), seminal root number, total root length, project root area, root surface area, and seminal root angle were measured after 6 days of seedling development. Grain yields (GY) were measured in a field experiment. A total of 29 QTLs were identified for seedlings cultured under WW regimes, and 23 QTLs under WS regimes. Individual QTL accounted for phenotypic variations ranging from 4.98 to 24.31 %. The QTLs were distributed on 17 chromosomes, except 1D, 4D, 6B and 6D. Seven consistently expressed QTLs were detected for all the traits tested except MRL under both water regimes. The QTLs for root traits were unevenly distributed among chromosomes, and clustered in eight loci on seven chromosomes, showing pleiotropic effects on target traits. One region in the interval Xgwm644.2- P6901.2 on chromosome 3B contained 9 QTLs affecting most root traits. The present data provide an insight into the genetic basis of seedling root development under different water regimes and may benefit breeding programs using marker-assisted selection (MAS) for root traits. [ABSTRACT FROM AUTHOR]

Wheat is the most important cereal in Central Asia (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan) and the Caucasus (Armenia, Azerbaijan and Georgia). Stripe rust, caused by Puccinia striiformis f. sp. tritici is considered the most important disease of wheat in Central Asia and the Caucasus (CAC). Although stripe rust has been present in the region for a long time, it has become a serious constraint to wheat production in the past 10 years. This is reflected by the occurrence of five epidemics of stripe rust in the CAC region since 1999, the most recent in 2010. Several wheat varieties occupying substantial areas are either susceptible to stripe rust or possess a low level of resistance. Information on the stripe rust pathogen in terms of prevalent races and epidemiology is not readily available. Furthermore, there is an insufficient understanding of effective stripe rust resistance genes in the region, and little is known about the resistance genes present in the commercial varieties and advanced breeding lines. The deployment of resistant varieties is further complicated by putative changes in virulence in the pathogen population in different parts of the CAC. Twenty four out of 49 improved wheat lines received through international nurseries or other exchange programs showed high levels of resistance to stripe rust to local pathogen populations in 2009. Fifteen of the 24 stripe rust resistant lines also possessed resistance to powdery mildew. It is anticipated that this germplasm will play an important role in developing stripe rust resistant wheat varieties either through direct adoption or using them as parents in breeding programs. [ABSTRACT FROM AUTHOR]

The frequency and pattern of irradiation-induced intergenomic chromosome rearrangements were analysed in the mutagenized (M0) and the first selfed (M1) generations of Triticum aestivum L. - Aegilops biuncialis Vis. amphiploids (2n = 70, AABBDDUbUbMbMb) by multicolour genomic in situ hybridization (mcGISH). mcGISH allowed the simultaneous discrimination of individual Ae. biuncialis genomes and wheat chromosomes. Dicentric chromosomes, fragments, and terminal translocations were most frequently induced by γ-irradiation, but centric fusions and internal exchanges were also more abundant in the treated plants than in control amphiploids. Rearrangements involving the Ub genome (Ub-type aberrations) were more frequent than those involving the Mb genome (Mb-type aberrations). This irradiation sensitivity of the Ub chromosomes was attributed to their centromeric or near-centromeric regions, since Ub-type centric fusions were significantly more abundant than Mb-type centric fusions at all irradiation doses. Dicentrics completely disappeared, but centric fusions and translocations were well transmitted from M0 to M1. Identification of specific chromosomes involved in some rearrangements was attempted by sequential fluorescence in situ hybridization with a mix of repeated DNA probes and GISH on the same slide. The irradiated amphiploids formed fewer seeds than untreated plants, but normal levels of fertility were recovered in their offspring. The irradiation-induced wheat - Ae. biuncialis intergenomic translocations will facilitate the successful introgression of drought tolerance and other alien traits into bread wheat. La fréquence et la nature des réarrangements chromosomiques intergénomiques induits par irradiation ont été analysés au sein de la génération irradiée (M0) et de la génération suivante (M1) d’amphidiploïdes Triticum aestivum L. - Aegilops biuncialis Vis. (2n = 70, AABBDDUbUbMbMb) par hybridation génomique in situ multicolore (mcGISH). L’hybridation mcGISH a permis de simultanément identifier les génomes de l’Ae. biuncialis et les chromosomes individuels du blé. Des chromosomes dicentriques, des fragments et des translocations terminales étaient les plus fréquemment induits par irradiation γ, mais des fusions centriques et des échanges internes étaient également plus abondants chez les plantes traitées que chez les amphidiploïdes témoins. Des réarrangements impliquant le génome Ub (aberrations de type Ub) étaient plus fréquentes que celles impliquant le génome Mb (aberrations de type Mb). Cette sensibilité à l’irradiation des chromosomes Ub a été attribuée à leurs régions centromériques ou péricentromériques puisque des fusions centriques de type Ub étaient significativement plus abondantes que les fusions centriques de type Mb à toutes les doses d’irradiation. Les chromosomes dicentriques ont totalement disparu tandis que les fusions centriques et les translocations étaient bien transmises de la M0 à la M1. L’identification de chromosomes spécifiques impliqués dans certains réarrangements a été tentée par hybridation in situ en fluorescence séquentielle avec une combinaison de plusieurs sondes d’ADN répétitif et d’hybridation GISH sur la même lame. Les amphidiploïdes irradiés ont formé moins de graines que les plantes témoins, mais des niveaux normaux de fécondité ont été retrouvés au sein de leur descendance. Les translocations intergénomiques blé - Ae. biuncialis induites par irradiation faciliteront l’introgression de la résistance à la sécheresse et d’autres caractères d’intérêt de l’espèce exotique vers le blé. [ABSTRACT FROM AUTHOR]

Two hundred and six varieties/lines of wheat were screened for stripe rust resistance. Eleven genotypes showed seedling as well as adult plant resistance against the 46S119 pathotype of stripe rust. The varieties/genotypes viz., HD2402, VL 404, WBM 1587, WBM 1591, WBM 1858, and WBM 1963 were identified as useful donors for stripe rust resistance in breeding programs because of their good agronomic backgrounds. The parents WBM 1587 and HS 240 were found to possess a single dominant gene pair for controlling inheritance of resistance against the 78S84 pathotype of stripe rust. [ABSTRACT FROM AUTHOR]

Morphogenetic processes in immature embryos of wheat ( Triticum aestivum L.) were investigated using a molecular marker for meristematic cells of cereals (proliferative antigen of meristem initial cells, PAIC). The used genetic model comprised a series of almost isogenic lines of wheat alternative by the alleles of dwarfing genes ( RhtB1c, RhtB1b, and Rht14) and the original cv. Saratovskaya 29. The Rht genetic system was found to affect the level of PAIC in the wheat callus cells during callus formation and subsequent regeneration. We found differences in the level of PAIC at certain stages of culturing and a general trend of its content in the course of callus formation and secondary differentiation in the callus tissue. Possible role of PAIC as a marker of meristematic centers within the callus tissue and the prospect of its use in breeding as an additional criterion for estimation of morphogenetic ability of the newly produced lines of wheat are discussed. [ABSTRACT FROM AUTHOR]

Wangshuibai is a Chinese landrace wheat with a high level of resistance to fusarium head blight (FHB) and deoxynivalenol (DON) accumulation. Using an F7 population of recombinant inbred lines (RILs) derived from the cross between Wangshuibai and Annong 8455 for molecular mapping of quantitative trait loci (QTL) for FHB resistance, the proportion of scabbed spikelets (PSS) and DON content were assessed under field conditions. Composite interval mapping revealed that two and three QTL were significantly associated with low PSS and low DON content, respectively, over 2 years. QTL on chromosomes 3B and 2A explained 17 and 11·5%, respectively, of the phenotypic variance for low PSS, whereas QTL on chromosomes 5A, 2A and 3B explained 12·4, 8·5 and 6·2%, respectively, of the phenotypic variance for low DON content. The 3B QTL appeared to be associated mainly with low PSS, and the 5A QTL primarily with low DON content in Wangshuibai. The 2A QTL had minor effects on both low PSS and DON content. Microsatellite and AFLP markers linked to these QTL should be useful for marker-assisted selection of QTL for low PSS and low DNA content from Wangshuibai. [ABSTRACT FROM AUTHOR]

A new cytoplasmic male-sterile (CMS) system for hybrid wheat breeding, YA-type CMS line with the cytoplasmic mutant from the common wheat variety ‘CA8057’, was developed by the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences. The pollen sterility of YA-type CMS line was easily maintained but difficult to restore. Some sterile lines with desirable agronomic performance, such as msYA-‘CA8057’ (BC17), msYA-‘Yuandong 6’ (BC9), msYA-‘Jin 411’ (BC9), msYA-‘WL1’ (BC10), msYA-‘Yanshi 9’ (BC10), msYA-‘BPm16’ (BC9), msYA-‘Jindong 8’ (BC9) and msYA-‘Jinmai 33’ (BC9), were bred and a restorer line GR1 was screened with 26 new restorer lines being developed by transferring restorer genes from GR1. It was found that abnormal phenomena occurred at the uninucleate-pollen stage and the abortive pollen was poor in starch content and other components. The variance analysis of agronomic traits in eight sterile lines indicated that there was no general negative effect of cytoplasm. The genetic analysis for fertility restoration showed that two pairs of independent major genes (designated YA Rf1YA Rf1YAr f2YAr f2) and some minor genes could be involved in the fertility restoration in restorer line GR1, and YA Rf1 was epistatic over YA Rf2 for the genetic effect of fertility restoration. As a new CMS system, the YA-type CMS line was of potential value for hybrid wheat breeding and should be further studied. [ABSTRACT FROM AUTHOR]

A doubled haploid population constructed from a cross between the South Australian wheat cultivars ‘Trident’ and ‘Molineux’ was grown under winter field conditions, under field conditions over summer and under artificial light both with and without vernalisation. The duration from planting to ear-emergence was recorded and QTL associated with heading date were detected using a previously constructed genetic linkage map. Associations were shown with chromosomal regions syntenous to previously identified photoperiod ( Ppd-B1) and vernalisation ( Vrn-A1) sensitive loci. Additional QTL associated with time to heading were also identified on chromosomes 1A, 2A, 2B, 6D, 7A and 7B. Comparisons between the genetic associations observed under the different growing conditions allowed the majority of these loci to be classified as having either photoperiod-sensitive, vernalisation-sensitive or earliness per se actions. The identification of a photoperiod-sensitive QTL on chromosome 1A provides evidence for a wheat gene possibly homoeologous to Ppd-H2 previously identified on chromosome 1H of barley. The occurrence of a putative major gene for photoperiod sensitivity observed on chromosome 7A is presented. The combined additive effects at these loci accounted for more than half the phenotypic variance in the duration from planting to ear-emergence in this population. The possible role of these loci on the adaptation of wheat in Australia is discussed. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB or head scab) has become a major limiting factor for sustainable wheat ( Triticum aestivum L.) production around the world. For quantitative trait loci (QTL) analysis of resistance to FHB, F3 plants and F3 : 5 lines, derived from a ‘Frontana’ (moderately resistant)/‘Seri82’ (susceptible) cross, were spray-inoculated in 2001 and 2002, respectively. Artificial inoculations were carried out under field conditions. Of 273 SSR and AFLP markers, 250 could be mapped and they yielded 42 linkage groups, covering a genetic distance of 1931 cM. QTL analysis was based on the constructed linkage map and area under the disease progress curve (AUDPC). The analyses revealed three consistent QTLs associated with FHB resistance on chromosomes 1BL, 3AL and 7AS explaining 7.9%, 7.7% and 7.6% of the phenotypic variation, respectively, above 2 years. The results confirmed the previously described resistance QTL of ‘Frontana’ on chromosome 3AL. A combination of ‘Frontana’ resistance with ‘Sumai-3’ resistance may lead to lines with augmented resistance expression. [ABSTRACT FROM AUTHOR]

Aluminum (Al) toxicity is one of the major constrains for wheat production in many wheat growing areas worldwide. Further understanding of inheritance of Al resistance may facilitate improvement of Al resistance of wheat cultivars ( Triticum aestivum L.). A set of ditelosomic lines derived from the moderately Al-resistant wheat cultivar Chinese Spring was assessed for Al resistance. The root growth of ditelosomic lines DT5AL, DT7AL, DT2DS and DT4DS was significantly lower than that of euploid Chinese Spring under Al stress, suggesting that Al-resistance genes might exist on the missing chromosome arms of 5AS, 7AS, 2DL and 4DL of Chinese Spring. A population of recombinant inbred lines (RILs) from the cross Annong 8455 × Chinese Spring-Sumai 3 7A substitution line was used to determine the effects of these chromosome arms on Al resistance. A genetic linkage map consisting of 381 amplified fragment length polymorphism (AFLP) markers and 168 simple sequence repeat (SSR) markers was constructed to determine the genetic effect of the quantitative trait loci (QTLs) for Al resistance in Chinese Spring. Three QTLs, Qalt.pser-4D, Qalt.pser-5A and Qalt.pser-2D, were identified that enhanced root growth under Al stress, suggesting that inheritance of Al resistance in Chinese Spring is polygenic. The QTL with the largest effect was flanked by the markers of Xcfd23 and Xwmc331 on chromosome 4DL and most probably is multi-allelic to the major QTL identified in Atlas 66. Two additional QTLs, Qalt.pser-5A and Qalt.pser-2D on chromosome 5AS and 2DL, respectively, were also detected with marginal significance in the population. Some SSR markers identified in this study would be useful for marker-assisted pyramiding of different QTLs for Al resistance in wheat cultivars. [ABSTRACT FROM AUTHOR]

Overall, 253 genomic wheat (Triticum aestivum) microsatellite markers were studied for their transferability to the diploid species Aegilops speltoides, Aegilops longissima, and Aegilops searsii, representing the S genome. In total, 88% of all the analyzed primer pairs of markers derived from the B genome of hexaploid wheat amplified DNA fragments in the genomes of the studied species. The transferability of simple sequence repeat (SSR) markers of the T. aestivum A and D genomes totaled 74%. Triticum aestivum – Ae. speltoides, T. aestivum – Ae. longissima, and T. aestivum – Ae. searsii chromosome addition lines allowed us to determine the chromosomal localizations of 103 microsatellite markers in the Aegilops genomes. The majority of them were localized to homoeologous chromosomes in the genome of Aegilops. Several instances of nonhomoeologous localization of T. aestivum SSR markers in the Aegilops genome were considered to be either amplification of other loci or putative translocations. The results of microsatellite analysis were used to study phylogenetic relationships among the 3 species of the Sitopsis section (Ae. speltoides, Ae. longissima, and Ae. searsii) and T. aestivum. The dendrogram obtained generally reflects the current views on phylogenetic relationships among these species. [ABSTRACT FROM AUTHOR]

On the basis of sequence analysis, 69 known low-molecular-weight glutenin subunit (LMW-GS) genes were experimentally classified into nine groups by the deduced amino acid sequence of the highly conserved N-terminal domain. To clarify the chromosomal locations of these groups, 11 specific primer sets were designed to carry out polymerase chain reactions (PCR) with the genomic DNA of group 1 ditelosomic lines of Chinese Spring, among which nine primer sets proved to be LMW-GS group-specific. Each group of LMW-GS genes was specifically assigned on a single chromosome arm and hence to a specific locus. Therefore, these results provided the possibility to predict the chromosome location of a new LMW-GS gene based on its deduced N-terminal sequence. The validity of the classification was confirmed by the amplifications in 27 diploid wheat and Aegilops accessions. The length polymorphisms of LMW-GS genes of groups 1 and 2, and groups 3 and 4.1 were detected in diploid A-genome and S-genome accessions, respectively. The diploid wheat and Aegilops species could be used as valuable resources of novel allele variations of LMW-GS gene in the improvement of wheat quality. The nine LMW-GS group-specific primer sets could be utilized to select specific allele variations of LMW-GS genes in the marker-assisted breeding. [ABSTRACT FROM AUTHOR]

Evaluation of wheat cultivars from different eras allows breeders to determine changes in agronomic and end-use quality characteristics associated with grain yield and end-use quality improvement over time. The objective of this research was to examine the trends in agronomic and end-use quality characteristics of hard red winter wheat cultivars grown in Nebraska. Thirty historically important and popular hard red winter wheat cultivars introduced or released between 1874 and 2000 were evaluated at Lincoln, Mead and North Platte, Nebraska in 2002 and 2003. An alpha lattice design with 15 incomplete blocks of two plots and three replications was used at all locations. Agronomic (days to flowering, plant height, spike length, culm length, grain yield and yield components, and grain volume weight) and end-use quality (flour yield, SDS-sedimentation value, flour protein content, and mixograph time and tolerance) traits were measured in each environment. Highly significant differences were observed among environments, genotypes and their interactions for most agronomic and end-use quality characteristics. Unlike modern cultivars, older cultivars were low yielding, and less responsive to favorable environments for grain yield and yield components. Semidwarf cultivars were more stable for plant height than traditional medium to tall cultivars. All cultivars had high grain volume weight since it is part of the grading system and highly selected for in cultivar release. Modern cultivars were less stable than older cultivars for SDS-sedimentation and mixing tolerance. However, the stability of older cultivars was attributed to their having weak mixing tolerance and reduced SDS-sedimentation values. The reduced protein content of modern cultivars was offset by increased functionality, as measured by mixograph and SDS sedimentation. In conclusion, breeders have tailored agronomic and end-use quality traits essential for hard red winter wheat production and marketing in Nebraska. [ABSTRACT FROM AUTHOR]

Wheat (Triticum aestivum L.) deletion (del) stocks are valuable tools for the physical mapping of molecular markers and genes to chromosome bins delineated by 2 adjacent deletion breakpoints. The wheat deletion stocks were produced by using gametocidal genes derived from related Aegilops species. Here, we report on the origin, structure, and behavior of a highly rearranged chromosome 1BS-4. The cytogenetic and molecular marker analyses suggest that 1BS-4 resulted from 2 breakpoints in the 1BS arm and 1 breakpoint in the 1BL arm. The distal segment from 1BS, except for a small deleted part, is translocated to the long arm. Cytologically, chromosome 1BS-4 is highly stable, but shows a unique meiotic pairing behavior. The short arm of 1BS-4 fails to pair with a normal 1BS arm because of lack of homology at the distal ends. The long arm of 1BS-4 only pairs with a normal 1BS arm within the distal region translocated from 1BS. Therefore, using the 1BS-4 deletion stock for physical mapping will result in the false allocation of molecular markers and genes proximal to the breakpoint of 1BS-4. [ABSTRACT FROM AUTHOR]

The maximum rate and duration for grain dry matter (DM) and nitrogen (N) accumulation were evaluated in 194 recombinant inbred lines (RILs) from a cross between the two French wheat cultivars Récital and Renan. These cultivars were previously identified as having contrasting kinetics of grain DM and N accumulation. Grain protein composition was analysed by capillary electrophoresis (CE), which enabled quantification of the different storage protein fractions (αβγ-gliadins, ω-gliadins, LMW glutenins, HMW glutenins, and each of their subunits). Correlation analyses revealed that DM and N accumulation rates were closely correlated and repeatable over several years, which was not the case for DM and N accumulation durations, and that protein composition was primarily influenced by the N accumulation rate. This was particularly true for the LMW-glutenins and the αβγ-gliadins, the most abundant protein fractions. A genetic map of 254 molecular markers covering nearly 80% of the wheat genome was used for quantitative trait loci (QTL) analysis. A total of seven QTLs were found. Five QTLs were significantly associated with the kinetics of DM and N accumulation, and two of them also influenced protein composition. Two QTLs affected only the protein composition. One major QTL explained more than 70% of the total variation in HMW-GS Glu1B-x content. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is one of the most important fungal wheat diseases worldwide. Understanding the genetics of FHB resistance is the key to facilitating the introgression of different FHB resistance genes into adapted wheat. The objectives of the present study were to detect and map quantitative trait loci (QTL) associated with FHB resistance genes and characterize the genetic components of the QTL in a doubled-haploid (DH) spring wheat population using both single-locus and two-locus analysis. A mapping population, consisting of 174 DH lines from the cross between DH181 (resistant) and AC Foremost (susceptible), was evaluated for type I resistance to initial infection during a 2-year period in spray-inoculated field trials, for Type II resistance to fungal spread within the spike in 3 greenhouse experiments using single-floret inoculation, and for resistance to kernel infection in a 2001 field trial. One-locus QTL analysis revealed 7 QTL for type I resistance on chromosome arms 2DS, 3AS, 3BS, 3BC (centromeric), 4DL, 5AS, and 6BS, 4 QTL for type II resistance on chromosomes 2DS, 3BS, 6BS, and 7BL, and 6 QTL for resistance to kernel infection on chromosomes 1DL, 2DS, 3BS, 3BC, 4DL, and 6BS. Two-locus QTL analysis detected 8 QTL with main effects and 4 additive by additive epistatic interactions for FHB resistance and identified novel FHB resistance genes for the first time on chromosomes 1DL, 4AL, and 4DL. Neither significant QTL by environment interactions nor epistatic QTL by environment interactions were found for either type I or type II resistance. The additive effects of QTL explained most of the phenotypic variance for FHB resistance. Marker-assisted selection for the favored alleles at multiple genomic regions appears to be a promising tool to accelerate the introgression and pyramiding of different FHB resistance genes into adapted wheat genetic backgrounds. [ABSTRACT FROM AUTHOR]

The genetics of Karnal bunt (KB) resistance were studied in populations derived from crosses of four resistant stocks (HD 29, W 485, ALDAN ‘S’/IAS 58, H 567.71/ 3*PAR) and a highly susceptible cultivar, WH 542. The plant materials screened for KB response consisted of F2, BC1 and RILs from all ‘Resistant’בSusceptible’ crosses and RILs from the six possible ‘Resistant’ × ‘Resistant’ crosses as well as the parents and F1s. The screening was performed under optimal conditions for disease development with a mixture of isolates from North Western Plains of India using the widely followed syringe method of inoculation. The KB scores of the F1 from the four ‘Resistant’ × ‘Susceptible’ crosses indicated partial dominance of resistance. Genetic analysis revealed that HD 29, W485 and ALDAN ‘S’/IAS 58 each carried two resistance genes whereas 3 genes were indicated in H 567.71/3*PAR. The six ‘Resistant × Resistant’ RIL sets showed that the genes in the four resistant stocks were different and that there may be as many as nine genes governing KB resistance in the four parents. [ABSTRACT FROM AUTHOR]

Yield and quality reductions caused byFusariumhead blight (FHB) have spurred spring wheat (Triticum aestivumL.) breeders to identify and develop new sources of host plant resistance. Four wheat synthetic hexaploids (× Aegilotriticumsp.) were developed, each having a quantitative trait locus (QTL),Qfhs.ndsu-3AS, providing FHB resistance fromTriticum turgidumL. var.dicoccoideschromosome 3A. Synthetics were produced by hybridizing a‘Langdon’– T. dicoccoides-recombinant chromosome 3A substitution line (2n = 4x = 28, AABB) with two accessions ofT. tauschii(2n = 2x = 14, DD). Synthetics were inoculated and evaluated for FHB resistance in two separate greenhouse seasons. One synthetic, 01NDSWG-5, exhibited FHB severity ratings of 36% and 32% in the separate seasons, compared with ratings of 9% and 30% for‘Alsen’, a FHB-resistant spring cultivar, and ratings of 70% and 96% for‘McNeal’, a susceptible spring cultivar, respectively. Synthetic × Alsen backcross-derived lines were produced to initiate combining different sources of FHB resistance. [ABSTRACT FROM AUTHOR]

Abstract: Kernel texture (hard vs soft grain) and more subtle within-class variations are known to have a large influence on end-use properties, mostly through the proportion of damaged starch and subsequent water requirement. In this study, quantitative trait loci (QTL) affecting kernel texture and dough rheology in a progeny from a cross between two ‘medium-hard’ wheat cultivars were identified and compared to the QTL locations for both traits. One hundred and sixty-five F7 recombinant inbred lines were studied in three environments in 1999. Kernel texture was estimated by both near infrared reflectance (NIR: HardNIR) and the single-kernel characterisation system (SKCS: HardSKCS). Dough rheology, taken as a predictor of end-use quality, was estimated by the empirical parameters measured by Chopin alveograph. The genetic map for this population consisted of 254 loci quite evenly distributed over the wheat genome. Considering only the QTL which were stable (detected in the three locations) and robust (through bootstrap resampling), five genomic regions were found to influence HardNIR, but only two of them are significant for HardSKCS, which was probably due to a less representative measure of the phenomenon. Eight QTLs were found for rheological traits. Some QTLs for dough rheology co-located with those for hardness or grain protein content, particularly on chromosomes 3A and 5B and close to the unlinked marker Xgwm130. According to trait, individual QTLs explained from 5.4 to 26.6% of the phenotypic variation and when taken together up to 46.0% of the variation. [Copyright &y& Elsevier]