A comparison of marker-assisted and phenotypic selection for high grain protein content in spring wheat

Wheat grain protein content (GPC) is a primary end-use quality determinant for hard spring wheat (Triticum aestivum L.), and marker-assisted selection (MAS) could help plant breeders to develop high GPC cultivars. Two experiments were conducted using two populations developed by crossing low GPC cultivars (Ember) and (McVey) with (Glupro), which contains a high GPC QTL from Triticum dicoccoides (DIC). In one experiment, MAS and phenotypic selection (PS) were employed to select high GPC genotypes, and the selected genotypes were grown in six North Dakota (ND), USA environments. In a second experiment, molecular markers were used to select BC₂F₂ plants from each marker class for the DIC allele from each population. These plants were twice self-pollinated to produce BC₂F₄ plants, which were grown in single ND and Minnesota (MN) environments. Mean GPC was highest among lines using PS at two environments and not significantly different between MAS and PS in the other four environments. Lines presumably homozygous for DIC alleles had significantly higher GPC than their respective low GPC parents. The phenotypic GPC variation explained by the markers (r ²) was 30% at the ND and 15% at the MN environment. The use of PS was as effective as MAS in selecting for high GPC genotypes and more effective in some environments. This likely can be attributed to PS enabling selection for both the major QTL and other genes contributing to GPC. The use of molecular markers might be more advantageous for transferring the high GPC DIC QTL in a backcrossing program during parent development.     

The effects of homoeologous group 3 chromosomes on grain colour dependent seed dormancy and brittle rachis in tetraploid wheat

`Langdon' (LDN), a durum wheat (Triticum turgidum L. var. durum) cultivar, and a set of chromosome substitution lines of Langdon, where A or B genome chromosome were replaced with a homologous chromosome of wild emmer wheat, T. turgidum ssp. dicoccoides (DIC), were used to assess the effect of the specific chromosome on seed dormancy in tetraploid wheat. The LDN(DIC 3A) and LDN (DIC 313) lines showed significantly lower seed germination than Langdon. It appears that LDN(DIC 3A) and LDN(DIC 3B) have red grain whose allele were designated as R-A1b and R-B1b, respectively and the rachises of LDN(DIC 3A) and LDN(DIC 3B) were fragile. The alleles for brittle rachis were designated as Br ₂ for LDN(DIC 3A) and Br ₃ for LDN(DIC 3B). From the F₂ of the crosses, Langdon/LDN(DIC 3A) and Langdon/LDN(DIC 3B), Br ₂ was located approximately 44.2 cM from the R-A1b locus and Br ₃ approximately 47.0 cM from the R-B1b locus, respectively. Recombinant inbred chromosomal lines for 3A and 3B were used to assess (1) the linkage relationship between grain colour and fragile rachis, and (2) the effect of grain colour on germination. Estimated distance between R-B1b – Br ₂ was 39.6 cM. For the 3A population, germination percentage of both colour groups was 12.4% for the red grain group and 68.6% for the amber group, respectively. For the 3B population, germination percentage of the red group was 7.3% and that of the amber group was 82.1%. For both populations, differences were statistical significant by t-tests. We considered that seed dormancy of T. turgidum ssp. dicoccoides was dependent on grain colour. It raised the possibility that brittle rachis is due to a paralogous gene set on homoeologous group 3 chromosomes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Increase in grain protein percentage in high-yielding common wheat breeding lines by genes from wild tetraploid wheat

Summary Forty-one breeding lines of common wheat, derived from crosses between the Israeli cultivars Miriam and Lakhish and high-protein lines of wild tetraploid wheat, Triticum turgidum var. dicoccoides, were tested for various protein and yield parameters in field trials, under typical agronomic conditions. All lines had a higher grain protein percentage (GPP) than the leading Israeli cultivar Deganit, which was grown as a control. Grain yield (GY) ranged in the breeding lines from a low of 2.44 t/ha to as high as that of Deganit (6.95 t/ha). Despite the weak negative correlation between GPP and GY, several lines excelled both in GPP and in GY. The grain protein yield (GPY) of some of these selected breeding lines was higher than that of Deganit; e.g., 1.19 t/ha in the best line vs. 1.02 t/ha in Deganit. The 16.7% increase in GPY in this line reflected a more efficient utilization of nitrogen.     

Intra- and inter-population variations in grain protein percentage in wild tetraploid wheat,Triticum turgidum var. dicoccoides

Summary Grain protein percentage (GPP) was studied in 910 accessions of the wild tetraploid wheat, Triticum turgidum var. dicoccoides, collected from 22 populations representing different ecogeographical conditions in Israel. High values of GPP were found, ranging from 19.7% to 28.0% for population means, and from 14.1% to 35.1% for single accessions. Marginal populations had usually lower GPP and smaller intra-population variation than central ones. Repeated sampling of some central populations for four consecutive years revealed relatively large intra-population fluctuations. A high and significant genetic component of variation was found within and between populations by a nested analysis of variance in two nurseries. However, the regression coefficients of parents vs. offsprings were relatively low, indicating a smaller genetic component of variation which may be accounted for by a significant genotype × environment interaction. No correlation was found between GPP and ecological factors, except for soil type: accessions growing on terra-rossa had higher GPP than those growing on basaltic soil. Accessions with black glumes, or with glabrous auricles, or with large grains exhibited high GPP values. A strategy for collecting accessions with high GPP is presented, and the potential use of high GPP genotypes in breeding programs is discussed.     

Genetics of morphological traits in wild wheat,Triticum turgidum var.dicoccoides

Summary The mode of inheritance, linkage groups, and chromosomal location of 23 morphological and 4 biochemical traits were characterized in the wild tetraploid emmer wheat,Triticum turgidum var.dicoccoides. These traits were described and their mode of inheritance was determined by their segregation in four F₂ populations derived from crosses between four var.dicoccoides accessions and a tetraploiddurum cultivar. Linkage groups among the genes encoding for these traits were determined or postulated, and their chromosomal location was deduced by linkage to previously located genes. The genetic control of the following traits was characterized and is first reported here: black keel; hairy leaf sheath; hairy auricles; hairy rachilla; hairy kernel brush; obtuse flag leaf; and curved neck/peduncle. The linkage data indicated that developmentally-related genes tended to occur in clusters.     

Plant nitrogen distribution in wild tetraploid (Triticum turgidum dicoccoides) and hexaploid wheat (Triticum aestivum)

Summary Differences were found in total nitrogen uptake and its pattern of distribution in the main tiller amongst five lines of wild tetraploid wheat (Triticum turgidum dicoccoides) and between it and two hexaploid wheats (Triticum aestivum) under low (48 ppm) and higher (240 ppm) levels of soil nitrogen.Under the low soil nitrogen level the hexaploids had higher amounts of total nitrogen in the main tiller than the dicoccoides lines, but under the higher soil nitrogen level, three of the dicoccoides lines had significantly (P<0.01) higher, and the other two lines, similar amounts as the hexaploids. The total amount of grain nitrogen in the hexaploids was significantly (P<0.01) higher than the five dicoccoides under the low nitrogen soil level but under the higher level, two of the dicoccoides lines had similar amounts as one of the hexaploids (cv. Bencubbin) but significantly (P<0.01) lower than the other (cv. Argentine IX).The efficiency of nitrogen translocation to the grain was significantly (P<0.01) lower in a primitive, compared with four cereal forms of dicoccoides under both low and high levels of soil nitrogen. The cereal forms of dicoccoides, while similar in nitrogen translocation efficiency under low soil nitrogen as the lower translocation efficiency hexaploid (cv. Bencubbin), were significantly (P<0.01) and substantially lower than it under the higher soil nitrogen level.     

Nitrogen uptake and remobilization in tetraploid 'Langdon' durum wheat and a recombinant substitution line with the high grain protein gene Gpc-B1

Tetraploid wheat (Triticum turgidum L. var. durum) cv. ‘Langdon’ (LDN) and its near‐isogenic recombinant substitution line no. 68 (RSL no. 68) carrying the high grain protein gene Gpc‐B1 from emmer wheat, were compared in three greenhouse experiments to establish in which way Gpc‐B1 increases grain protein concentration (GPC). At anthesis, RSL no. 68 had higher soluble protein and amino acids concentrations in the flag leaf than LDN. At maturity, both lines presented a similar above ground biomass and grain yield. However, RSL no. 68 showed a higher total N content in ears, grain and chaff than LDN; N harvest index (NHI) was also higher because of a lower straw N concentration and higher grain N concentration. When both lines were grown with a low N supply, and when N supply was interrupted before anthesis, similar trends were observed but the differences in GPC were smaller. It is concluded that RSL no. 68 accumulates a higher GPC than LDN mainly because of a more efficient N remobilization from the leaves to the ears during grain filling.     

Location of genes for high grain protein percentage and other quantitative traits in wild wheat Triticum turgidum var. dicoccoides

Summary The genetic control of grain protein percentage (GPP) in the wild tetraploid wheat, Triticum turgidum var. dicoccoides, was determined by crossing four accessions of this taxonomic variety with durum cultivar Inbar, and analyzing the parents, F₁ and F₂ populations. Reciprocal crosses indicated no cytoplasmic effect on GPP. The F₂ variation was continuous in all crosses, showing no transgressive segregation. However, crosses between different accessions of var. dicoccoides showed transgressive segregation indicating the presence of different genes for high GPP in these accessions. Grain protein percentage was mostly codominant with high GPP, showing either no dominance, or a weak dominance. Heritability coefficients (broad sense) ranged from 0.30 to 0.53. Correlation coefficients between GPP and yield components were usually significantly negative, with the exception of the number of spikelets per spike, and in some crosses, grain weight.The number and chromosomal location of genes coding for high GPP were determined by the association between GPP and 27 markers (23 morphological and 4 biochemical markers). For this purpose, the genetic control of these markers, their linkage groups and chromosomal location were studied. At least four loci for high GPP that segregated in the F₂ populations are suggested: one on chromosome arm 1AS, marked by the black glume gene (Bg); one on 1BS, marked by the HMW gliadin locus Gli-B1; one on group 5, marked by the genes for beaked glume (Bkg) and toothed palea (Tp); and one on group 7, marked by the kinky neck gene (Kn). The relationship between GPP and several yield components was studied in a similar manner. In general, loci of markers that correlated positively with high GPP were not correlated with a decrease in yield components. Moreover, several loci of var. dicoccoides were associated with an increase in yield components.The utilization of markers for chromosomal location of genes coding for quantitative traits is compared to the technique of aneuploid analysis, commonly used in wheat. The significance of the above findings for breeding is discussed.     

Agronomic and qualitative traits of T. turgidum ssp. dicoccum genotypes cultivated in Italy

Summary The increasing popularity of organic agriculture and health food products has led to a renewed interest in hulled wheat species such as emmer (Triticum turgidum ssp. dicoccumSchubler). Knowledge on agronomic and quality traits is required for effective and efficient use of germplasm collections in breeding programs. The objective of this study was to estimate agronomic and grain quality traits of emmer wheat cultivated in Italy. A total of 20 emmer accessions consisting of landraces, breeding lines or cultivars selected from landraces and modern cultivars were examined under low input conditions. The study was conducted for three successive years (2002–2004) at one location of Southern Italy (Foggia). The entries were characterized for agronomic and qualitative traits [grain yield (t ha⁻¹), thousand grain weight (g), test weight (kg hl⁻¹), grain protein content (%), HMWG composition, dry gluten content (%), gluten index and yellow index, alveograph indices and Total Organic Matter (TOM) on cooked pasta]. The results showed a large genetic variability for most of the traits measured and, even if most of the accessions showed inferior bread- and pasta-making performance, modern cultivars exhibited improved quality traits with some potential to perform healthy and tasty food.     

Wheat pollen dispersal under semiarid field conditions: potential outcrossing with Triticum aestivum and Triticum turgidum

Isolation distance is the main barrier to crop-to-crop gene-flow. A 3-year study assessed the maximum potential outcrossing under field conditions between two wheat cultivars (Triticum aestivum L.) and between wheat and durum wheat (Triticum turgidum L. var. durum). Outcrossing was measured by seed set on emasculated recipient plants placed at four sides with different distances from a 3 m × 3 m T. aestivum (cultivar Chinese Spring) pollen source. Frequencies of seed set at 0 m distance were 45% (37–56%) for T. aestivum cultivars and 18% (5–30%) with T. turgidum. These values agree with hybridization in non-limiting pollen conditions measured by manual crosses in greenhouse. The number of pollen grains and the outcrossing frequencies decreased at increasing distances influenced by the prevailing wind direction. Under semiarid conditions of this assay, viable pollen was found 14 m from the pollen source, with a maximum distance of 8 m at which cross-pollination decreases below 1%. Ambient conditions affect pollen viability, hybridization and pollen dispersal. Data presented in this paper emphasize the major role played by environmental conditions in outcrossing. Data obtained in one area may therefore not coincide with the prevailing situation in different locations and climates.     

The introduction into bread wheat of a major gene for resistance to powdery mildew from wild emmer wheat

Summary A new source of resistance to wheat powdery mildew caused by Erysiphe graminis has been transferred to hexaploid bread wheat, Triticum aestivum, from the wild tetraploid wheat, Triticum dicoccoides. The donor was crossed to bread wheat and the pentaploid progeny was then self-pollinated. Plants having a near stable hexaploid chromosome complement were selected in the F₃ progeny and topcrossing and backcrossing of these to a second wheat cultivar to improve the phenotype was undertaken. Monosomic analysis of early backcross lines showed the transferred gene to be located on chromosome 4A. The gene has been designated Pm16.     

Evaluation of slow rusting resistance components to leaf rust in CIMMYT durum wheats

Information about slow rusting resistance to leaf rust (Puccinia triticina) in durum wheat (Triticum turgidum var. durum) is limited. Three slow rusting components, latent period, receptivity, and uredinium size, were determined at the adult plant stage for seven durums with slow rusting resistance to leaf rust and two susceptible durums in three greenhouse experiments. Additionally, area under the disease progress curve (AUDPC) and final disease severity (FDS) were determined in three field trials under artificial epidemics with the same P. triticina race BBG/BN. Compared to the most susceptible check, the AUDPC and FDS of slow rusting resistant durums were significantly lower and ranged from 13–47 to 22–59%, respectively. The latent period was significantly longer (8.5–10.3 days) and uredinium size significantly smaller (8.1–14.8 × 10⁻² mm²) on slow rusting durums than on the susceptible checks (8.0 days and 17.3–23.8 × 10⁻² mm², respectively). Uredinium size was the most stable slow rusting component across experiments. Correlations between uredinium size versus AUDPC and uredinium size versus FDS for each environment were high (r = 0.86–0.88). Correlations between latent period and field parameters were significant (r = −0.60 to −0.80). Correlations between receptivity and the field parameters were not significant. A multiple regression analysis showed that the variation in AUDPC and FDS was significantly explained only by uredinium size (P < 0.0001). The best slow rusting resistant lines can be used for developing high-yielding durums with more durable resistance to leaf rust.     

Transfer of high kernel weight and high protein from wild tetraploid wheat (Triticum turgidum dicoccoides) to bread wheat (T. aestivum) using homologous and homoeologous recombination

Summary Wheat pentaploids were produced by hybridizing a high kernel weight (1000 grain wt=56 g), high protein (25.4%) line of wild tetraploid wheat (Triticum turgidum dicoccoides) as male parent, with the three hexaploids (T. aestivum) — normal Chinese Spring and its two homoeologous pairing mutants, ph _1b and ph ₂. The pentaploids were crossed as female parents to the two commercial hexaploid cultivars Warigal and Barkaee and 42-chromosome stable plants selected from the F₁ of the pentaploid x hexaploid crosses.Mean protein content of certain F₃ lines from all six pentaploid x hexaploid crosses was significantly higher than Chinese Spring and the respective commercial hexaploid parent (p<0.005) indicating high protein had been transferred from the tetraploid to the hexaploid level.Kernel weight amongst certain F₃ lines of the three pentaploids x Barkaee was significantly (p<0.0005) higher than either Chinese Spring or Barkaee, indicating the transfer also of high kernel weight from the tetraploid to the hexaploid level. However kernel weight was not significantly increased over Warigal in any F₃ lines of its crosses with the three pentaploids.High levels of homoeologous chromosome pairing in the ph-mutant pentaploids, plus evidence for significant modification of the composition of high-molecular weight (HMW) glutenin subunits of grain protein in certain F₃ derivatives of the ph-mutant pentaploid x hexaploid, crosses indicates that the ph-mutant-derived lines may possess novel (intergenome) genetic recombination, at least for high protein, and possibly kernel weight.     

Expression of a Triticum turgidum var. dicoccoides source of Fusarium head blight resistance transferred to synthetic hexaploid wheat

Yield and quality reductions caused by Fusarium head blight (FHB) have spurred spring wheat (Triticum aestivum L.) breeders to identify and develop new sources of host plant resistance. Four wheat synthetic hexaploids (×Aegilotriticum sp.) were developed, each having a quantitative trait locus (QTL), Qfhs.ndsu‐3AS, providing FHB resistance from Triticum turgidum L. var. dicoccoides chromosome 3A. Synthetics were produced by hybridizing a ‘Langdon’‐T. dicoccoides‐ recombinant chromosome 3A substitution line (2n = 4x = 28, AABB with two accessions of T. 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.     

Cytological and microsatellite mapping of the genes determining liguleless phenotype in durum wheat

Liguleless phenotypes of wheat lack ligule and auricle structures on all leaves of the plant. Two recessive genes principally control the liguleless character in tetraploid wheat. The F₂ progenies of k17769 (liguleless mutant)/Triticum dicoccoides and k17769/T. dicoccum segregated in a 15:1 ratio, whereas the F₂ progenies of k17769/T. durum and k17769/T. turgidum segregated in a 3:1 ratio. A new gene, lg₃, was found on chromosome 2A. Segregation of F₂ progenies between k17769 and chromosome substitution lines for homoeologous group 2 chromosomes suggested that the liguleless genotype had occurred by mutation at the lg₃ locus on chromosome 2A, and then by mutation at the lg₁ locus on chromosome 2B, in the process of domestication of tetraploid wheat. The gene (lg₁) was linked to Tc₂ (11.9 cM), which determines phenol colour reaction of kernels, on the long arm of chromosome 2B. The distance of lg₁ to the centromere was found to be 60.4 cM, and microsatellite mapping established the gene order, centromere – Xgwm382 – Xgwm619 – Tc₂ – lg₁ on the long arm of chromosome 2B.     

Variation for resistance to head blight caused by Fusarium graminearum in wild emmer (Triticum dicoccoides) originating from Israel

Head blight of wheat (FHB, scab) caused by Fusarium spp. has been associated with yield and quality losses in many wheat-growing regions. In tetraploid wheat sources of resistance are scarce. In the search for novel sources of resistance, 151 Triticum dicoccoides genotypes, originating from 16 habitats in Israel and one habitat in Turkey together with several control genotypes, were evaluated for reaction to fungal spread (Type II resistance) in replicated greenhouse experiments. Significant genetic diversity was found among the tested genotypes, the broad sense heritability for Type II FHB resistance was 0.71. Most of the tetraploid accessions were highly susceptible, only a few showed moderate resistance. Among the eight T. dicoccoides lines with the lowest relative infection rates, five originated from the Mt. Gerizim population, and three from the Mt. Hermon population. None of the T. dicoccoides lines reached the level of resistance present in the common wheat cultivar Sumai3. This revised version was published online in July 2006 with corrections to the Cover Date.     

Resistance of wild emmer wheat to stem rust: Ecological,pathological and allozyme associations

Summary Seedling resistance to wheat stem rust was determined in populations of wild emmer wheat, Triticum dicoccoides, and characterized by means of ecological factors and allozyme genotypes. Reactions to wheat stem rust were studied in 102 single plant accessions of T. dicoccoides from ten populations by inoculation with Puccinia graminis tritici race 14, isolate GSR-739. Six populations displayed different degrees of response polymorphism with reactions ranging from high resistance to complete susceptibility, whereas four populations contained only susceptible plants. In some of the accession, unexplained intrasib variation in resistance and intraplant variation of infection-types were found. Resistance to stem rust was negatively correlated with two ecological factors, altitude and number of Sharav (hot-dry) days which are unfavorable to disease development. Variation in stem rust response was shown to exist in ecogeographic regions where climatic variables enhanced the development of the fungus, conceivably maintained by natural selection. Likewise, allozyme genotypes, single or in multiple loci combinations, appeared to be associated with resistance or susceptibility to rust. Such association need to be verified by genetic studies in order to become established as useful markers.     

Molecular cytogenetic characterization of wheat-Thinopyrum ponticum translocations bearing blue-grained gene(s) induced by r-ray

Eight γ-irradiation-induced Triticum aestivum – Thinopyrum ponticum translocations conveying the blue aleurone were characterized using molecular cytogenetic approach. The size of alien chromosome segments was estimated by genomic in situ hybridization (GISH). The wheat chromosome segments involved in these translocations were clearly identified by two-color fluorescence in situ hybridization (FISH) with the probes of pAs1 and pSc119.2 (or pHvG38). Most of the detected translocations were reciprocal translocations involving wheat chromosomes 1B, 2D, 3A, 4A, 5B, 6B, 6D and 7A. This series of blue-grained wheat translocation lines would be useful in theoretical studies and wheat chromosome engineering breeding.     

Endosperm peroxidase electrophoresis patterns to distinguish tetraploid from hexaploid wheats

Summary A simple method is proposed to distinguish hexaploid (Triticum aestivum L.) from tetraploid (Triticum turgidum L., durum wheat) cultivated wheats on the basis of peroxidase isozymes coded by genome D. It can also be used as a first step to detect possible contamination by tetraploid genotype mixtures. The peroxidase patterns of endosperm and of embryo plus scutellum found among 349 entries of a durum wheat world basis collection are shown.     

Use of the gene pools of Triticum turgidum ssp. dicoccoides and Aegilops squarrosa for the breeding of common wheat (T. aestivum), through chromosome-doubled hybrids

Summary Triticum turgidum ssp. dicoccoides (wild emmer wheat, AABB, 2n=28) and Aegilops squarrosa (goat grass, DD, 2n=14) comprise a rich reservoir of valuable genetic material, which could be useful for the breeding of common wheat (T. aestivum, AABBDD, 2n=42). Many accessions of both wild species, most of them selected for resistance to stripe rust, were used to make amphiploids. Two strategies were applied: (1) the production of autopolyploid cytotypes of the wild species, followed by hybridisation, and (2) the production of allotriploid interspecific hybrids, followed by doubling of the number of chromosomes. The first route was unsuccessful because of failure of the crosses between the autopolyploid cytotypes, possibly due to incongruity between the two species and to reduced fertility in the autopolyploid cytotypes. The second route yielded the desired synthetic hexaploids. However, the rate of success of the crosses was low and there were great differences between years, and within years between crosses. Embryo rescue was applied to obtain the primary hybrids (2n=21), which were highly sterile and had on average 0.3 bivalents and 20.4 univalents per pollen mother cell. Various abnormalities were recorded. Doubling of the number of chromosomes sometimes occurred spontaneously or was brought about by colchicine treatment. The large scale of the interspecific hybridisation programme ensured that one-third of the female and one-sixth of the male accessions were represented in the synthetic hexaploids.