Development of RAPD markers in tritordeum and addition lines of Hordeum chilense in Triticum aestivum

RAPD markers were developed for octoploid X Tritordeum (amphiploid Hordeum chilense × Triticum aestivum) and its parents. Two bread wheats, two H. chilense accessions and the two tritordeums synthesized with them were used. A total of 41 arbitrary decamer primers were tested, yielding 190 products that could be assigned to wheat, 185 to H. chilense and 108 that were nonspecific (present in wheat and barley). A total of 44 products were specific to one H. chilense line and 33 to the other 16 of the former were located on the chromosomes using a set of H. chilense in T. aestivum addition lines. The potential of RAPDs for developing addition lines or the detection of introgressions of H. chilense in bread wheat is discussed.     

Chromosomal location of resistance to Septoria tritici in Hordeum chilense determined by the study of chromosomal addition and substitution lines in `Chinese Spring' wheat

Hordeum chilense exhibits resistance to Septoria tritici. Addition and substitution lines of H. chilensein wheat were utilized in growth chamber and field experiments to determine which H. chilense chromosomes carry resistance genes. Resistance is conferred by gene(s) on chromosome 4 and, to a minor extent, by genes on chromosomes 5, 6 and 7. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genome discrimination and chromosome pairing in the Hordeum chilense × Aegilops tauschii amphiploid

Tritordeum (X Tritordeum Ascherson et Graebner) is a synthetic amphiploid belonging to the Triticeae tribe, which resulted from crosses between Hordeum chilense and wheat. It presents useful agronomic traits that could be transferred to wheat, widening its genetic basis. In situ hybridisation with total genomic DNA from H. chilense and cloned, repetitive DNA sequences (pTa71 and pAs1) probes were used to discriminate the parental origin of all chromosomes, to analyse the chromosome pairing and to identify the chromosomes in pollen mother cells (PMCs) at metaphase I of the tritordeum line HT251 (H^chH^chDD, 2n = 4x = 28). The H. chilense total genomic DNA and the ribosomal sequence pTa71 probes, allowed the unequivocal discrimination of the 14 chromosomes of H^ch genome-origin and the 14 chromosomes of D genome-origin. Chromosome pairing analysis revealed meiotic irregularities such as reduced percentage of PMCs with complete homologous pairing, high frequency of univalents, most of H. chilense-origin and a reduced frequency of intragenomic multivalents from both genomes. The H. chilense genome revealed high meiotic instability. After individual chromosome identification at metaphase I with the pAs1 probe, we found the occurrence of pairing between chromosomes of different homoeology groups. The possible interest of the tetraploid tritordeum in the improvement of other Triticeae species is also discussed.     

Location of genes controlling resistance to greenbug (Schizaphis graminum Rond.) in Hordeum chilense

Wheat/Hordeum chilense disomic addition lines have been used to locate genes influencing resistance against greenbug (Schizaphis graminum Rond.) in specific chromosomes of H. chilense. H. chilense is a source of antixenosis, antibiosis and host tolerance to the greenbug, being resistant also to the Russian wheat aphid, the two key pests in wheat. For measuring antixenosis, the numbers of aphids per plant were recorded in a host free choice test; antibiotic resistance was determined by measuring the developmental time, the fecundity and the intrinsic rate of population increase of aphids reared on the different hosts, and host tolerance to aphids was evaluated by the leaf damage and the number of expanded leaves on the hosts after 3 weeks of infestation. The greenbugs belonged to a clone of biotype C. Plant genes with positive effects for antixenosis were located on chromosome 1H^ch. Genes with positive effects for antibiosis were located on three different chromosomes and those that prolonged aphid developmental time were located on chromosomes 5H^ch and 7H^ch while those that reduced the total fecundity were on 4Hch. Chromosome 7H^ch accounted for host tolerance to greenbug.     

Screening for Greenbug Resistance in Hordeum chilense Roem et Schult.

Schizaphis graminum (Rondani) is a serious pest of cultivated wheat (Triticum aestivum L.) and resistance is only available in other related species such as Hordeum chilense. Amphiploids between H. chilense and Triticum spp. have been obtained, and addition lines of H. chilense in wheat have been developed. Thirty-five accessions of H. chilense were screened to identify greenbug antixenosis, antibiosis and tolerance. Antixenosis was determined in a conventional host free choice test; antibiosis was measured by aphid life cycle and fecundity rate, and tolerance was tested in a conventional infestation test of 4 weeks. Two commercial barley cultivars were used as susceptible and resistant controls. Eight H. chilense accessions showed higher degrees of antixenosis than the resistant check, 19 were similar and the rest were lower. All accessions were more resistant than the susceptible check. Measured by aphid life cycle, 22 H. chilense accessions showed higher antibiosis than the resistant cv., and all exhibited a higher antibiotic effect on fecundity rates than the control. A similar degree of tolerance to that of the resistant control was observed in six accessions, the remaining entries ranged between the controls. The presence of one mechanism did not exclude the existence of other mechanisms in the same entry and therefore, independence of the different mechanisms is proposed. Most of the accessions showed higher variability than both controls for the three mechanisms, and it appears to be genetic variability within entries for the three mechanisms.     

Genetics of Hordeum chilense– Current Status

Hordeum chilense, a South-American wild barley, is being used in cereal breeding because of its good crossability with both wild and cultivated Triticeae species. Amphiploids and chromosome addition lines of H. chilense in common and durum wheats have been obtained as a means to transfer desirable agronomic characters from wild barley to wheat. No allosyndetic pairing has been detected in diverse hybrids involving H. chilense. Several biochemical markers have been associated with the seven chilense chromosome pairs. New approaches are necessary to transfer genes from H. chilense to cereals.     

Use of ccSSR markers for the determination of the purity of alloplasmic wheat in different Hordeum cytoplasms

We tested three different consensus chloroplast simple sequence repeat (ccSSR) primers to identify amplified polymorphic products in Hordeum chilense, Hordeum vulgare and other Triticeae species with a double aim. First, to use chloroplast‐specific primers as an indirect method for the assessment of wheat cytoplasmic male sterile purity in seedlings during multiplication and in the development of alloplasmic lines. Second, to analyse cytoplasmic relationships among H. chilense accessions and between H. chilense and other members of the Triticeae tribe. The products from primer ccSSR‐4 were easily discriminated using agarose gel electrophoresis. Based on the lengths of amplification products, three groups were identified: the first included almost exclusively H. chilense accessions, the second contained H. vulgare accessions and the third comprised the wheat and the rest of the analysed accessions. Sequencing of PCR products revealed point mutations and insertions/deletions in addition to the expansion/contraction of the microsatellite repeat length. Data analyses of sequenced fragments revealed six groups of accessions among the material studied. No significant differences were found among H. chilense accessions.     

Chromosomal localization of genes for carotenoid pigments using addition lines of Hordeum chilense in wheat

×Tritordeum sp. (Ascherson et Graebner) is the amphiploid obtained after chromosome doubling of hybrids between Hordeum chilense (Roem. et Schult.) and diploid, tetraploid or hexaploid wheats. Tritordeums have consistently higher carotenoid pigment contents than durum or bread wheat. Two distinct H. chilense accessions (used for the synthesis of tritordeum) were analysed for this trait. The chromosomal localization of the genes coding the ability of H. chilense to increase the carotene content of wheat were carried out using two sets of wheat- H. chilense addition lines. The a arm of chromosome 7H^ch is proposed to be responsible for the high carotene content in tritordeum. The implication of this finding in wheat breeding is discussed.     

Nearly Total Absence of Homoeologous Pairing in a Hybrid between Tetraploid Hordeum chilense and Triticum aestivum

A hybrid between an induced tetraploid of Hordeum chilense (2n = 28 = H^chH^chH^chH^ch) and Triticum aestivum var. ‘Chinese Spring’ (2n = 42 = AABBDD) has been produced to test gene effects of this wild barley on homoeologous pairing in wheat. Cytological investigations in metaphase I have shown that the hybrid, which is perennial like H. chilense but morphologically more similar to the wheat parent, possesses the expected genome composition H^chH^ch ABD and a stable euploid chromosome number of 2n = 35. Pairing among the homologous H. chilense chromosomes was almost complete. The level of non-homologous chromosome association proved to be lower than the range of pairing known from euhaploids of ‘Chinese Spring’.     

Short Communication Resistance to common bunt in Hordeum chilense X Triticum spp. Amphiploids

The reaction of tritordeum and its Hordeum chilense and Triticum spp. parents to common bunt incited by Tilletia tritici were determined in field experiments. H. chilense accessions were very resistant, and durum wheats exhibited high to moderate levels of resistance. Conversely, bread wheats were highly susceptible. Resistance from H. chilense was expressed in the amphiploids, although the level of resistance was partially diluted at higher ploidy levels. Hexaploid tritordeums were immune to the disease; some infection was observed among the octo-ploids but at much lower levels than in their respective wheat parents.     

A physical map of chromosome 4Hch from H. chilense containing SSR, STS and EST-SSR molecular markers

The construction of a physical map of chromosome 4H^ch from Hordeum chilense containing molecular markers capable of detecting segments of this chromosome in a wheat background would be very useful for marker-assisted introgression of 4H^ch chromatin into both durum and common wheat. With this aim, the applicability of 106 barley chromosome 4H primers (62 SSRs and 44 STSs) to amplify markers showing polymorphism between H. chilense and both common or bread and durum wheat was investigated. Twenty-five SSR (40.3%) and six STS (13.6%) barley primer pairs consistently amplified H. chilense products. Eight SSR (12.9%) and four STS (9.1%) barley primers were polymorphic between H. chilense and both common and durum wheat, 10 of them (6 SSRs and 4 STSs) were located on chromosome 4H^ch using both the addition line of chromosome 4H^ch in Chinese Spring wheat and a tritordeum line (an amphiploid between H. chilense and T. turgidum) nullisomic for chromosome 4H^ch. Additionally, 18 EST-SSR barley markers previously located on chromosome 4H^ch were screened for polymorphism; 15 were polymorphic between H. chilense and both durum and common wheat. For physical mapping we used a ditelosomic tritordeum line for the short arm of chromosome 4H^ch and a tritordeum line homozygous for a 70% terminal deletion of the long arm of 4H^ch. A total of 25 markers (6 SSRs, 4 STSs and 15 EST-SSRs) were mapped to chromosome 4H^ch. Eight markers were allocated on the 4H^chS, eight were mapped in the 30% proximal region of 4H^chL and nine were on the 70% distal region of 4H^chL, respectively. Arm location on barley chromosome 4H was also carried out using both 4HS and 4HL ditelosomic addition lines in wheat. All markers mapped may have a role in marker-assisted introgression of chromatin segments of chromosome 4H^ch in both durum and common wheat backgrounds. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Characterization of a set of common wheat–Hordeum chilense chromosome 7Hch introgression lines and its potential use in research on grain quality traits

Chromosome 7H^ch from Hordeum chilense has potential for improving seed carotenoid content in wheat as it carries a Phytoene synthase 1 (Psy1) gene, which has a major role in this trait. Structural changes in chromosome 7H^ch were obtained in common wheat background by crossing the wheat disomic substitution line 7H^ch(7D) with a disomic addition line carrying chromosome 2C^c from Aegilops cylindrica in common wheat cv. ‘Chinese Spring’. Rearranged 7H^ch chromosomes were cytologically characterized by FISH. A set of 24 molecular markers and the Psy1 gene were used to identify the H. chilense chromosome segments involved in the introgressions. Six structural rearrangements of chromosome 7H^ch were identified. They included three homozygous wheat–H. chilense centromeric translocations, one involving the 7H^chS arm (T‐7H^chS·A/B) and two involving the 7H^chL arm (T1‐7H^chL·A/B and T2‐7H^chL·A/B). In addition, one 7H^chS arm deletion, one 7H^chL·7H^chL isochromosome and one 7H^chS telosome were obtained in hemizygous condition. These genetic stocks will be useful for studying the effect of chromosome 7H^ch on wheat flour colour.     

The reaction of x Tritordeum and its Triticum spp. and Hordeum chilense parents to rust diseases

Summary Hexaploid and octoploid tritordeums and their parents Hordeum chilense and Triticum spp. were screened for resistance to isolates of wheat and barley yellow and brown rusts. All H. chilense lines were highly resistant to both wheat and barley brown rust, few lines were susceptible to wheat yellow rust while susceptibility to barley yellow rust was common. In general the resistance of tritordeum is predominantly contributed by the wheat parent and apparently the genes for resistance in H. chilense are inhibited in their expression by the presence of the wheat genome.Abbreviations WYR wheat yellow rust - WBR wheat brown rust - BYR barley yellow rust - BBR barley brown rust     

Development and cytogenetic characterisation of a double goat grass-barley chromosome substitution in tritordeum

×Tritordeum (Ascherson et Graebner, an amphiploid between Triticum turgidum conv. durum and Hordeum chilense), and chromosome substitution lines of tritordeum where chromosomes 2 H ^ch or 3 H ^ch H. chilense were replaced with chromosome 2 D of T. aestivum or 3 H ^v chromosome of H. vulgare, respectively, were used to assess the effect of specific chromosomes on the rachis. ×Tritordeum has brittle rachis while the 2 D(2 H ^ch) and 3 H ^v (3 H ^ch) substitution lines have non-brittle rachis. Both lines also have compact spikes, a character highly desirable for the improvement of tritordeum threshability. Different combinations of 2 D and 3 H ^v translocations were developed in tritordeum. In this article we present information on the identification and characterisation of all these introgression lines by the fluorescent in situ hybridisation.     

Application of C-banding and fluorescence in situ hybridization for the identification of the trisomics of Hordeum chilense

Hordeum chilense is a wild barley species that has a high degree of genetic variability and significant potential for use in plant breeding. To establish a series of trisomics in H. chilense (2n = 14), plants with 2n + 1 chromosome numbers were isolated from the progenies of selfed triploid plants. Based on both fluorescent in situ hybridization with pAs1 and pTa71 repetitive DNA probes and C-banding patterns, seven different trisomics were tentatively identified. Primary trisomic plants were for chromosomes 1H^ch, 4H^ch, 5H^ch, 6H^ch and 7H^ch. A secondary trisomic carrying a 5H^chS-5H^chS isochromosome as the extra chromosome and a trisomic for chromosome 3H^ch heterozygous for the 3H^chS-4H^chL and 4H^chS–3H^chL interchange were identified. The trisomic for chromosome 1H^ch cannot be phenotypically distinguished from the diploid. The rest of the trisomic types were distinguishable from the diploid by their morphological characteristics (relatively poor vigour, decreased size and shorter spikes) but they were morphologically indistinguishable from each other. The frequencies of trisomics among the progenies derived from self-fertilization of these aneuploids ranged from 10.7% to 37.5%, with an average frequency of 26.1%. This revised version was published online in July 2006 with corrections to the Cover Date.     

The inheritance and chromosomal location of morphological traits in wild wheat, Triticum turgidum L. ssp. dicoccoides

The homoeologous groups of chromosomes carrying the genes for some morphological traits in wild wheat Triticum turgidum L. ssp. dicoccoides (T. dicoccoides) were determined, but not the actual chromosomes carrying them. The objectives of this study were to investigate the modes of inheritance, and determine the chromosomes carrying some morphological traits in wild emmer (2n = 28; AABB), the progenitor of most cultivated wheats. To investigate the inheritance of morphological traits, crosses were made between T. turgidum L. ssp. durum (T. durum cultivar Chartokhmi (IR10) and T. dicoccoides accessions TA1150 and TA1131. F₂ seeds from each cross were grown in the field and six qualitative characters were investigated. Purple coleoptile, purple auricle, purple culm, hairy auricle, hairy rachilla, and fragility of spike were controlled by single dominant genes. To determine the chromosomal locations, accession TA1131 was crossed with the complete set of LDN D-genome disomic substitution lines. Assessments of F₂ populations showed that chromosomes 7A, 6A, 7B, 5B, 5A and 3B carried genes for purple coleoptile, purple auricle, purple culm, hairy auricle, hairy rachilla and brittle rachis, respectively.     

Genetic variation for carotenoid pigment content in the amphiploid Hordeum chilense × Triticum turgidum conv. durum

Hexaploid tritordeum, the amphiploid Hordeum chilense x Triticum turgidum conv. durum has a higher grain carotene content than durum wheat. In order to decide strategies for introgressing this character into durum wheat, the effect on the carotene content of tritordeum synthesized with H. chilense and durum wheat differing in carotene content was analysed. Carotene content was evaluated in 35 primary tritordeum lines and their parents, 27 H. chilense accessions and 19 durum wheat cultivars. Some amphiploids have either one barley or wheat parent in common. In general, the influence of H. chilense is more important than that of wheat in the amphiploid carotene content. Nevertheless, the interactions between both parents on the amphiploid carotene content are also important.     

Effects of Hordeum chilense cytoplasm on agronomic traits in common wheat

The genome of bread wheat, AABBDD, was substituted into the cytoplasm of Hordeum chilense by repeated backcrossing to produce alloplasmic lines. The aim of this work was to investigate the effect of H. chilense cytoplasm on agronomic traits in common wheat. Three cytolines were developed. The alloplasmic nature of these lines was confirmed using chloroplast simple‐sequence repeat markers. Each cytoline was compared with its respective euplasmic control for agronomic performance during 2 years of field trials. The interaction between H. chilense cytoplasm and common wheat genome greatly affected most of the traits evaluated. Among them, alloplasmic lines showed delayed anthesis date, lower yield and lower plant height. These effects are similar to those caused by Aegilops cytoplasm. The main conclusion of this work is that H. chilense cytoplasm is of limited value for wheat breeding.     

Homoeological relationships between the f chromosome of Brassica rapa and the e chromosome of Brassica oleracea

Eight plants of the putative double monosomic addition line (DMAL, 2n= 20) were developed by crossing a monosomic chromosome addition line of radish [f(A)‐type monosomic addition line (MAL) (2n= 19)] carrying the f chromosome of Brassica rapa (2n= 20, AA) with another [e(C)‐type MAL (2n= 19)] having the echromosome of Brassica oleracea (2n= 18, CC). The homoeological relationships between the two alien chromosomes were investigated by morphological, cytogenetic and random amplified polymorphic DNA (RAPD) analysis. Seventeen morphological traits that were not present in the radish cv. ‘Shogoin’ were observed in both MALs and these traits were substantially exhibited in DMAL plants. At the first metaphase of pollen mother cells (PMCs), the two parental MALs showed a chromosome configuration of 9II +1I, demonstrating impossibility of recombination between the R and the added chromosomes. The DMALs formed 10II in approximately 73% of PMCs, with one bivalent showing loose pairing between two chromosomes differing in size. In an attempt to identify the two MALs by RAPD‐specific markers using 26 selected random primers, 13 and 20 bands were specific for the f(A)‐type and the e(C)‐type MALs, respectively; 12 bands were common to both MALs (26.7%). In conclusion, the f chromosome of B. rapa is homoeologous to the e chromosome of B. oleracea. The genetic domain (genes) for 17 morphological traits are linked to each homoeologous chromosome bearing 27% of the corresponding RAPD markers.     

Agroinoculation of Tomato Yellow Leaf Curl Virus (TYLCV) Overcomes the Virus Resistance of Wild Lycopersicon Species

Accessions of the wild tomato species Lycopersicon chilense LA 1969 and L. hirsutum LA 1777 which are resistant to tomato yellow leaf curl virus (TYLCV) in field- and in whitefly-mediated transmission tests were agroinoculated with a tandem repeat of the TYLCV genome. Large amounts of viral DNA started to accumulate in the agroinoculated L. chilense and L. hirsutum plants about 10 days after the agroinoculation. Yellowing and narrowing of the upper leaves were observed in the L. chilense plants but no curling as in susceptible L. esculentum cultivars. The agroinoculated L. hirsutum plants showed typical yellowing and curling of young leaves. These findings indicate that TYLCV introduced by means of agroinoculation leads to the breakdown of natural resistance mechanisms which prevent the replication, spread and expression of symptoms in resistant tomato genotypes.