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.     

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.     

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.     

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.     

Molecular mapping of genes determining hairy leaf character in common wheat with respect to other species of the Triticeae

Two major genes controlling leaf pubescence were mapped on chromosomes 4BL (Hl1) and 7BS (Hl2 ^Aesp ) in wheat (Saratovskaya 29) and a wheat/Aegilops introgression line (102/00^I), respectively, together with quantitative trait loci (QTLs) determining hairiness of the leaf margin (QHl.ipk-4B, QHl.ipk-4D) and auricle (QPa.ipk-4B, QPa.ipk-4D) on the long arms of chromosomes 4B and 4D, respectively. The QTLs on chromosome 4D were contributed by a synthetic wheat and, therefore, originated from Aegilops tauschii. The homoeologous group 4 wheat/A. tauschii genes/QTLs detected in the present study were aligned with the barley pubescence genes Hln/Hsh and Hs _b and the hairy peduncle rye gene Hp1. The locus seems to be pleiotropically responsible for the pubescence of different plant organs in different species of the Triticeae. Another homoeologous series may be present on the short arms of the homoeologous group 7 chromosomes, based on the results of an allelic test cross between the Chinese local cultivar Hong-mang-mai carrying Hl2 and the wheat/Aegilops speltoides introgression line 102/00^I.     

Cytology, Fertility and Morphology of Amphiploids Hordeum chilense × Tetraploid Wheats (Tritordeum)

With the aim of widening the genetic variability of hexaploid tritorceum through the wheat parents, amphiploids between Hordeum chilense and Triticum turgidum ssp. dicoccoides, ssp. georgicum, and Cody, polonicum have been synthesized. The meiotic behaviour and the fertility were examined in these amphiploids. The morphology of the amphiploids in comparison to their wheat parents was described.     

The association of genes for purple coleoptile with chromosomes of the wheat variety Mironovskaya 808

Summary The association of genes for purple pigment in the coleoptile with the chromosomes of the winter wheat variety Mironovskaya 808 was investigated using monosomic F₂ analysis. The segregation ratio for F₂ hybrids of Chinese Spring monosomics x Mironovskya 808 seems to indicate that the purple colour of the coleoptile is determined by two dominant genes, Rc₃ and Rc₄, which are located on the chromosomes 7D and 6B respectively, and which reinforce each other. Apart from these two genes, suppressors found on the chromosomes 2A, 2B, 2D, 4B and 6A also play a role in the intensity of the purple colour.With the aid of a Chinese Spring telocentric chromosome marker it was observed that the Rc₃ gene is located on the chromosome arm 7DS, at a distance of 16±4.23 crossover units from the centromere.     

Mapping genes controlling anthocyanin pigmentation on the glume and pericarp in tetraploid wheat (<Emphasis Type="Italic">Triticum durum</Emphasis> L.)

A novel gene, designated Pg (purple glume), controlling anthocyanin pigmentation of the glume was identified and mapped in an F₂ population from the durum wheat (Triticum durum) cross TRI 15744/TRI 2719. This gene was close to one of the two complementary dominant genes, controlling anthocyanin pigmentation of the pericarp (gene Pp3) in the centromere region of chromosome 2A; the other Pp gene (Pp1) was mapped on the short arm of chromosome 7B, near gene Pc controlling anthocyanin pigmentation of the culm and co-segregating with Pls (purple leaf sheath) and Plb (purple leaf blade). On the basis of the mapping results, the Pp3, Pc, Pls and Plb genes of T. durum were regarded as allelic to the T. aestivum Pp3, Pc-B1, Pls-B1 and Plb-B1 loci. The likely allelism of Pp1 in T. durum and T. aestivum remains in dispute, the present durum Pp gene mapped to the short arm of chromosome 7B, whereas in common wheat it was reportedly located on the long arm.     

Telosomic mapping of the homoeologous genes for the long glume phenotype in tetraploid wheat

Triticum turgidum ssp. polonicum and T. ispahanicum were characterized by the long glume phenotype. P ₁ gene determines the long glume phenotype of T. polonicum, and locates on chromosome 7A. T. ispahanicum has shorter glume than T. polonicum and the long glumephenotype is determined by P ₂ gene located on chromosome 7B. In the present study, aneuploid stocks of `Langdon' durum wheat were used to map the genes, P ₁ and P ₂. P ₁ located on the long arms of chromosome 7A and its map distances from the centromere was 14.5 cM. On chromosome 7B, four loci located as cc (chocolate black chaff) – Pc (purple culm) – centromere – P ₂ – cn-BI (chlorina). P ₂ located on the long arms of chromosome 7B and its map distances from the centromere was 11.7 cM. It was suggested that a paralogous gene set conditions long glume phenotype in the homoeologous group 7 chromosomes. The P ₁ and P ₂ genes may be useful as genetic markers in tetraploid wheat.     

The addition of Hordeum chilense chromosomes to Triticum turgidum conv. durum. biochemical,karyological and morphological characterization

Summary Biochemical, karyological and morphological characterization of Triticum turgidum conv. durum/Hordeum chilense addition forms was carried out. Nine H. chilense isozyme markers, belonging to ACPH, CPX, EST, PGM, 6-PGD, GOT and MDH enzymatic systems, were used to identify the chilense chromosomes in 50 monosonic or polysomic addition forms. Several morphological traits were associated with the presence of chilense chromosome in the complement. The transmission frequencies of addition chilense chromosomes were also investigated in the offspring of various crosses.     

Levels of phenotypic variation for developmental traits in landrace genotypes of durum wheat (Triticum turgidum ssp. Turgidum L. conv. durum (Desf.) MK.) from Jordan

Summary A germplasm collection comprising 132 landrace genotypes of durum wheat (Triticum turgidum) ssp. turgidum L. conv. durum (Desf.) MK., from 10 districts in Jordan was evaluated for days to booting (DB), days to heading (DH), days to anthesis (DA), days to maturity (DM), filling period (FP) and grain yield (GY). In spite of the relatively strong genetic (Gr) and phenotypic (Pr) correlation coefficients between the developmental traits, the variation among genotypes was significant. GY was only positively and significantly correlated with DA and FP, while it was negatively correlated with DH. Genotypes with different combinations of early, medium and late developmental traits have been identified. Different combinations of DH and FP may or may not lead to differences in DM and GY. However, genotypes with long FP and medium-late DH gave the highest grain yield. Multiple linear regression of the duration of maturity (M) stage on the duration of booting (B), heading (H) and anthesis (A) stages (M = –260.87 + 2.09 B + 1.23 H + 0.9 A, R ² = 0.92) indicates that it is possible to manipulate the duration of these developmental stages and develop genotypes with high yield potential and early maturity, a highly desirable in drought-prone environments.     

Seed Storage Proteins of Triticum turgidum ssp. dicoccoides and Their Effect on the Technological Quality in Durum Wheat

F₄ progenies of a cross between durum wheat cultivar ‘Creso’ and an accession of Triticum turgidum ssp. dicoccoides with high protein content were analysed by two different electrophoretic procedures (A-PAGE and SDS-PAGE). Variation of storage proteins at the Glu-A1, Glu-B1, Glu-B3 and Gli-B1 loci was studied. Electrophoretic analyses have shown that parents contain different alleles at each of the four loci considered and that protein components of T. dicoccoides are uncommon among cultivated wheats. Recombination between the Glu-B3 and Gli-B1 loci was observed. To determine the effects of the allelic variants on gluten properties, F₅ grains from every F₄ line were analysed for protein content and SDS-sedimentation value. Gluten quality was strongly associated with the allelic type of proteins coded by the Glu-B3 locus and, to a lesser extent, to those coded by Glu-A1. Mean sedimentation value of progenies possessing the ‘Creso’Glu-B3 allele was significantly greater than that showing the T. dicoccoides allele. High molecular weight glutenin sub-units coded by the T. dicoccoides Glu-A1 locus were also associated with larger sedimentation values than null form of ‘Creso’. Results of SDS-test, obtained for recombinants between Glu-B3 and Gli-B1, confirmd that specific omega- and gamma-gliadins are only genetic markers of quality, whereas variation for LMW glutenin subunits coded at Glu-B3 is responsible for differences in gluten properties.     

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.     

Agronomical performance and breeding value of selected strains of diploid wheat,Triticum monococcum

Summary Twenty-one germplasm accessions and breeding lines of einkorn wheat (Triticum monococcum ssp. monococcum and ssp. sinskajae) were grown at two sites in Italy and evaluated for various field and seed characteristics. Grain yields of germplasm accessions were relatively high (317–3238 kg/ha), but distinctly lower than those of four modern cultivars of tetraploid (T. turgidum ssp. durum) and hexaploid wheat (T. aestivum ssp. Aestivum) included in the experiments as controls. As expected, all Einkorns-including some substantially higher yielding crossbred lines (3415–4362 kg/ha)-were defective for one or more agronomically relevant features. However, a few of the accessions examined were found to contain, as a group, practically all the genes needed to breed monococcums having the main field attributes of a modern wheat cultivar: high yielding capacity, good threshability, large kernel size, earliness, short stature and adequate lodging resistance. Still higher yielding diploid wheats, more responsive to improved growing conditions and of better seed quality, could probably be obtained from crosses with wild monococcums bearing mostly two-seeded florets and with accessions producing less slender-shaped kernels. Some of the Einkorns examined were found to carry minor genes for easy threshing which might enhance the efficacy of the major gene for soft glumes carried by T. monococcum ssp. sinskajae, a partially free-threshing diploid wheat taxon. Seed protein percentage of monococcums was markedly higher than that of durum and bread wheat cultivars even in those cases where their grain yields surpassed those of the polyploid checks. The possibilities offered by diploid wheat in the exploitation of novel endosperm mutants and F₁ hybrid vigour, as well as in the fields of celiac disease, crop diversification and resistance to agro-biological stresses are discussed. Breeding priorities and strategies are also proposed.     

Phenotypic variation in root architecture traits and their relationship with eco-geographical and agronomic features in a core collection of tetraploid wheat landraces (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L.)

To obtain varieties with root systems adapted to marginal environments it is necessary to search for new genotypes in genetically diverse materials, such as landraces that are more likely to carry novel alleles for different root features. A core collection of ‘durum’ wheat, including three subspecies (dicoccon, turgidum and durum) from contrasting eco-geographical zones, was evaluated for root traits and shoot weight at the seminal root stage. Distinctive rooting phenotypes were characterized within each subspecies, mainly in subsp. durum. Contrasting rooting types, including large roots with shallow distributions, and others with high root numbers were identified. Correlations with climatic traits showed that root shape is more relevant in adaptation to eco-geographical zones in subsp. dicoccon, whereas in subsp. turgidum and durum, which come from warmer and drier areas, both size and shape of roots could have adaptive roles. Root traits with the largest positive effects on certain yield components under limited water conditions included root diameter in subsp. dicoccon, root size in turgidum, and root number in durum. Additionally, shoot weight at the seedling stage had important effects in subsp. turgidum and durum. Twenty-eight marker–trait associations (MTAs) previously identified in this collection for agronomic or quality traits were associated with seminal root traits. Some markers were associated with only one root trait, but others were associated with up to six traits. These MTAs and the genetic variability characterized for root traits in this collection can be exploited in further work to improve drought tolerance and resource capture in wheat.     

Expression of 17 rye (Secale cereale L.) traits in a range of durum wheat (Triticum durum Desf.) and bread wheat (T. aestivum L.) genetic backgrounds

Summary Expression of 17 rye traits in 24 bread wheat x rye and 8 durum wheat x rye crosses was studied, using a self-compatible, homozygous, dwarf rye. Rye showed epistasis for hairiness on the peduncle in all the crosses of Triticum aestivum and T. durum wheats with rye. Dark greenness of leaves of rye was expressed in all the durum wheat x rye and in some of the bread wheat x rye crosses. Similarly, absence of auricle pubescence, a rye trait, was expressed in most of the durum wheat x rye crosses but not in the bread wheat x rye crosses, indicating the presence of inhibitors for these traits frequently on the D genome and rarely on the A and/or B genome of wheat. Most of the wide hybrids resembled rye fully or partially for intense waxy bloom on the leaf-sheath and for the absence of basal underdeveloped spikelets. Similarly, most of the amphihaploids resembled rye for the anthocyanin in the coleoptile, stem and node. The presence of some inhibitors on A and/or B genome of wheat was indicated in some of the wheat genotypes for the expression of rye traits viz. intense waxy bloom, anthocyanin in node and absence of basal underdeveloped spikelets. Enhancement in the level of expression of the intensity and length of bristles on the mid-rib of the glume of the hybrids might be due to wheat-rye interaction. Less number of florets/spikelet as in rye showed variable expression in different wheat backgrounds. Some other rye traits like absence of auricles, terminal spikelet and glume-awn were not expressed in the wheat background. The expression of some of the rye genes might have been influenced by their interaction with Triticum cytoplasm and/or the environment.     

Cytogenetic analysis of wild emmer populations from Turkey and Israel

Summary Chromosome behavior during meiosis of the F₁ hybrids involving two races of wild emmer Triticum turgidum var. dicoccoides and var. timopheevi is described. Four of the six Turkish accessions were similar to the Israeli group in pairing relationships and seed set percentages. The collection (# 189) is cytologically similar to var. timopheevi. The other Turkish accession (# 191) showed good chromosome pairing with both var. dicoccoides and var. timopheevi.     

Chromosome locations of leaf rust resistance genes in selected tetraploid wheats through substitution lines

Langdon durum D-genome disomic substitution lines were used to study the chromosome locations of adult-plant leaf rust resistance genes identified from tetraploid wheat accessions. The accessions are 104 (Triticum turgidum subsp. dicoccum var. arras) and 127 (T. turgidum subsp. durum var. aestivum). The complete sets of the substitution lines were crossed as female parents with the accessions and F₁ double monosomic individuals selected at metaphase I. Segregating F₂ individuals were inoculated during the flag leaf stage with pathotype UVPrt2 of Puccinia triticina. The substitution analysis involving accession 104 showed that the gene for leaf rust resistance is located on chromosome 6B. The analysis with accession 127 indicated that chromosome 4A carries a gene for leaf rust resistance. The two novel genes are temporarily designated as Lrac104 and Lrac127, respectively from accessions 104 and 127.     

Formation of unreduced gametes is impeded by homologous chromosome pairing in tetraploid <Emphasis Type="Italic">Triticum turgidum</Emphasis> × <Emphasis Type="Italic">Aegilops tauschii</Emphasis> hybrids

It is believed that unreduced gametes with somatic chromosome numbers play a predominant role in natural polyploidization. Allohexaploid bread wheat originated from spontaneous hybridization of Triticum turgidum L. with Aegilops tauschii Coss. Unreduced gametes originating via meiotic restitution, including first-division restitution (FDR) and single-division meiosis (SDM), are well documented in triploid F₁ hybrids of T. turgidum with diploid Ae. tauschii (genomic constitution ABD, usually with 21 univalents in meiotic metaphase I). In this study, two T. turgidum lines known to carry genes for meiotic restitution were crossed to tetraploid Ae. tauschii. The resulting F₁ hybrids (genomes ABDD), had seven pairs of homologous chromosomes and regularly formed 14 univalents and seven bivalents at metaphase I. Neither FDR nor SDM were observed. The distribution of chromosome numbers among progeny obtained by self pollination and a backcross to T. turgidum showed the absence of unreduced gametes. These results suggest that high homologous pairing interfered with meiotic restitution and the formation of unreduced gametes. This may be related to asynchronous movement during meiosis between paired and unpaired chromosomes or to uneven distribution of chromosomes in anaphases, resulting in nonviable gametes.