The addition of Dasypyrum villosum (L.) Candargy chromosomes to durum wheat (Triticum durum Desf.)

Molecular Cytogenetic Identification of the Wheat–Dasypyrum villosum T3DL·3V#3S Translocation Line with Resistance against Stripe Rust

The annual species Dasypyrum villosum possesses several potentially valuable genes for the improvement of common wheat. Previously, we identified a new stripe rust-resistant line, the Chinese Spring (CS)–D. villosum 3V#3 (3D) substitution line (named CD-3), and mapped its potential rust resistance gene (designated as YrCD-3) on the 3V#3 chromosome originating from D. villosum. The objective of the present study was to further narrow down the YrCD-3 locus to a physical region and develop wheat-3V#3 introgression lines with strong stripe rust resistance. By treating CD-3 seeds with 60Co γ-irradiation, two CS-3V#3 translocation lines, T3V#3S.3DL and T3DS.3V#3L (termed 22-12 and 24-20, respectively), were identified from the M4 generation through a combination of non-denaturing fluorescence in situ hybridization (ND-FISH) and functional molecular markers. Stripe rust resistance tests showed that the line 22-12 exhibited strong stripe rust resistance similarly to CD-3, whereas 24-20 was susceptible to stripe rust similarly to CS, indicating that YrCD-3 is located on the short arm of 3V#3. The line 22-12 can potentially be used for further wheat improvement. Additionally, to trace 3V#3 in the wheat genetic background, we produced 30 3V#3-specific sequence tag (EST) markers, among which, 11 markers could identify 3V#3S. These markers could be valuable in fine-mapping YrCD-3.

Pairing and Exchanging between Daypyrum villosum Chromosomes 6V#2 and 6V#4 in the Hybrids of Two Different Wheat Alien Substitution Lines

Normal pairing and exchanging is an important basis to evaluate the genetic relationship between homologous chromosomes in a wheat background. The pairing behavior between 6V#2 and 6V#4, two chromosomes from different Dasypyrum villosum accessions, is still not clear. In this study, two wheat alien substitution lines, 6V#2 (6A) and 6V#4 (6D), were crossed to obtain the F₁ hybrids and F₂ segregating populations, and the testcross populations were obtained by using the F₁ as a parent crossed with wheat variety Wan7107. The chromosomal behavior at meiosis in pollen mother cells (PMCs) of the F₁ hybrids was observed using a genomic in situ hybridization (GISH) technique. Exchange events of two alien chromosomes were investigated in the F₂ populations using nine polymerase chain reaction (PCR) markers located on the 6V short arm. The results showed that the two alien chromosomes could pair with each other to form ring- or rod-shaped bivalent chromosomes in 79.76% of the total PMCs, and most were pulled to two poles evenly at anaphase I. Investigation of the F₂ populations showed that the segregation ratios of seven markers were consistent with the theoretical values 3:1 or 1:2:1, and recombinants among markers were detected. A genetic linkage map of nine PCR markers for 6VS was accordingly constructed based on the exchange frequencies and compared with the physical maps of wheat and barley based on homologous sequences of the markers, which showed that conservation of sequence order compared to 6V was 6H and 6B > 6A > 6D. In the testcross populations with 482 plants, seven showed susceptibility to powdery mildew (PM) and lacked amplification of alien chromosomal bands. Six other plants had amplification of specific bands of both the alien chromosomes at multiple sites, which suggested that the alien chromosomes had abnormal separation behavior in about 1.5% of the PMCs in F₁, which resulted in some gametes containing two alien chromosomes. In addition, three new types of chromosome substitution were developed. This study lays a foundation for alien allelism tests and further assessment of the genetic relationship among 6V#2, 6V#4, and their wheat homoeologous chromosomes.

Molecular Genotyping (SSR) and Agronomic Phenotyping for Utilization of Durum Wheat (Triticum durum Desf.) Ex Situ Collection from Southern Italy: A Combined Approach Including Pedigreed Varieties

In South Italy durum wheat (Triticum durum Desf.) has a long-time tradition of growing and breeding. Accessions collected and now preserved ex situ are a valuable genetic resource, but their effective use in agriculture and breeding programs remains very low. In this study, a small number (44) of simple sequence repeats (SSR) molecular markers were used to detect pattern of diversity for 136 accessions collected in South Italy over time, to identify the genepool of origin, and establish similarities with 28 Italian varieties with known pedigree grown in Italy over the same time-period. Phenotyping was conducted for 12 morphophysiological characters of agronomic interest. Based on discriminant analysis of principal components (DAPC) and STRUCTURE analysis six groups were identified, the assignment of varieties reflected the genetic basis and breeding strategies involved in their development. Some “old” varieties grown today are the result of evolution through natural hybridization and conservative pure line selection. A small number of molecular markers and little phenotyping coupled with powerful statistical analysis and comparison to pedigreed varieties can provide enough information on the genetic structure of durum wheat germplasm for a quick screening of the germplasm collection able to identify accessions for breeding or introduction in low input agriculture.

Interspecific and intergeneric hybridization as a source of variation for wheat grain quality improvement

The hybridization events with wild relatives and old varieties are an alternative source for enlarging the wheat quality variability. This review describes these process and their effects on the technological and nutritional quality. Wheat quality and its end-uses are mainly based on variation in three traits: grain hardness, gluten quality and starch. In recent times, the importance of nutritional quality and health-related aspects has increased the range of these traits with the inclusion of other grain components such as vitamins, fibre and micronutrients. One option to enlarge the genetic variability in wheat for all these components has been the use of wild relatives, together with underutilised or neglected wheat varieties or species. In the current review, we summarise the role of each grain component in relation to grain quality, their variation in modern wheat and the alternative sources in which wheat breeders have found novel variation.

Chromosomal localization of genes conferring desirable agronomic traits from Agropyron cristatum chromosome 1P

Agropyron cristatum (L.) Gaertn. (2n = 4x = 28, PPPP), a wild relative of common wheat, possesses many potentially valuable genes for wheat breeding. To transfer these genes into wheat, a series of wheat-A. cristatum derivatives have been obtained in our laboratory. In this study, a wheat-A. cristatum derivative II-3-1 was obtained, which was proven to contain a 1P (1A) disomic substitution and 2P disomic addition line with 40 wheat chromosomes and two pairs of A. cristatum chromosomes by genomic in situ hybridization (GISH) and molecular markers analysis. By further backcrossing with the wheat parent Fukuhokomugi (Fukuho) and self-fertilization, three different lines were separated from II-3-1, including wheat-A. cristatum 1P disomic addition line II-3-1a, 2P disomic addition line II-3-1b and 1P (1A) disomic substitution line II-3-1c. Because 2P addition line had been reported before, we aimed to investigate 1P disomic addition line II-3-1a and wheat-A. cristatum 1P (1A) disomic substitution line II-3-1c. Analysis of different genetic populations demonstrated that 1P chromosome harbored multiple agronomic traits, such as elevated spike length, increased tillering ability, reduced plant height and spikelet density. Besides, bristles on the glume ridges as an important morphological marker was located on 1P chromosome. Therefore, the novel 1P addition and substitution lines will be used as important genetic materials to widen the genetic resources of wheat.

Induction of 4VS chromosome recombinants using the CS ph1b mutant and mapping of the wheat yellow mosaic virus resistance gene from Haynaldia villosa

The wheat spindle streak mosaic virus (WSSMV) or wheat yellow mosaic virus (WYMV) resistance gene, Wss1, from Haynaldia villosa, was previously mapped to the chromosome arm 4VS by the development of 4V (4D) substitution and T4DL·4VS translocation lines. For better utilization and more accurate mapping of the Wss1, in this research, the CS ph1b mutant was used to induce new translocations with shortened 4VS chromosome fragments. Thirty-five homozygous translocations with different alien fragment sizes and breakpoints of 4VS were identified by GISH and molecular marker analysis. By field test, it was found that all the identified terminal translocations characterized as having smaller 4VS chromosome segments in the chromosome 4DS were highly resistant to WYMV, while all the interstitial translocations with 4VS inserted into the 4DS were WYMV susceptible. Marker analysis using 32 4VS-specific markers showed that both the terminal and interstitial translocations had different alien fragment sizes. Five specific markers could be detected in the WYMV-resistant terminal translocation line NAU421 with the shortest introduced 4VS fragment, indicating they can be used for marker-assisted selection in wheat breeding. Based on the resistance evaluation, GISH and molecular marker analysis of the available translocations, the gene(s) conferring the WYMV resistance on 4VS could be further cytologically mapped to the distal region of 4VS, immersed in the bin of FL 0.78-1.00. The newly developed small fragment translocations with WYMV resistance and 4VS specific markers have laid solid groundwork for the utilization in wheat breeding for WYMV resistance as well as further cloning of Wss1.

Development of a set of compensating Triticum aestivum-Dasypyrum villosum Robertsonian translocation lines

Dasypyrum villosum (L.) Candargy, a wild relative of bread wheat ( Triticum aestivum L.), is the source of many agronomically important genes for wheat improvement. Production of compensating Robertsonian translocations (cRobTs), consisting of D. villosum chromosome arms translocated to homoeologous wheat chromosome arms, is one of the initial steps in exploiting this variation. The cRobTs for D. villosum chromosomes 1V, 4V, and 6V have been reported previously. Here we report attempted cRobTs for wheat - D. villosum chromosome combinations 2D/2V, 3D/3V, 5D/5V, and 7D/7V. The cRobTs for all D. villosum chromosomes were recovered except for the 2VS and 5VL arms. As was the case with the 6D/6V combination, no cRobTs involving 2D/2V chromosomes were recovered; instead, cRobT T2BS·2VL involving a nontargeted chromosome was recovered. All cRobTs are fertile, although the level of spike fertility and hundred kernel weight (HKW) varied among the lines. The set of cRobTs involving 12 of the 14 D. villosum chromosomes will be useful in wheat improvement programs. In fact, among the already reported cRobTs, T6AL·6VS carrying the Pm21 gene is deployed in agriculture and many useful genes have been reported on other cRobTs including resistance to stem rust race UG99 on T6AS·6VL.

Cytogenetics of Triticum × Dasypyrum hybrids and derived lines

Genomic in situ hybridization was used to study Triticum x Dasypyrum wide hybrids and derived lines. A cytogenetic investigation was carried out in progenies of (i) amphiploids derived from T. turgidum var. durum (T. durum; 2n = 14; genomes AABB) x D. villosum (2n = 14; genome VV), (ii) three-parental hybrids (T. durum x D. villosum) x T. aestivum (2n = 42, genomes A'A'B'B'D'D'), and (iii) T. aestivum aneuploid lines carrying D. villosum chromosomes or chromatin. The amphiploids derived from T. durum x D. villosum showed a stable chromosomal constitution, made up of 14 V chromosomes, 14 chromosomes carrying the wheat A genome and 14 chromosomes carrying the B genome. High karyological instability was observed in the progenies of three-parental hybrids ([T. durum x D. villosum] x T. aestivum). Plants having the expected 14 A chromosomes, 14 B chromosomes, 7 D chromosomes, and 7 V chromosomes were rather rare (4.5%). Many progeny plants (45.5%) had the hexaploid wheat genome with 42 chromosomes and lacked any detectable D. villosum chromatin. Other plants (50%) had 14 A chromosomes and 14 B chromosomes, plus variable numbers of D and V chromosomes, the former being better retained than the latter in most cases. Some T. aestivum lines carrying D. villosum chromosomes or chromatin, as the result of addition, substitution, or recombination events or even a combination of these karyological events, were found to be stable. Other lines were unstable, and these lines carried 1V, 3V, or 5V chromosomes or their portions. Substitution or recombination events where 1V chromosomes were involved could concern the homeologous counterparts in both the A and B and D genomes of wheat. No line could be recovered where the shorter arm of 3V chromosomes was present. Changes in the morphology and banding pattern of V chromosomes were observed in hybrids that did not carry the entire D. villosum complement. By comparing the results of our cytogenetic analyses with certain phenotypic characteristics of the lines studied, genes for discrete traits could be assigned to specific V chromosomes or V chromosome arms. From the frequency of V chromosomes that were involved in chromatin exchanges with or substituted for one of their homeologous counterparts in the A, B, and D wheat genomes, it was inferred that D. villosum belongs to the same phyletic lineage as T. urartu (donor of the A genome of wheat) and Aegilops speltoides (B genome), and that Ae. squarrosa (D genome) diverged earlier from D. villosum.

Evaluation of Dasypyrum villosum Populations for Resistance to Cereal Eyespot and Stripe Rust Pathogens

Resistance to Pseudocercosporella herpotrichoides (cause of eyespot) and Puccinia striiformis(cause of stripe rust) was evaluated in a germ plasm collection of Dasypyrum villosum (syn. Haynaldia villosa) and a set of disomic addition lines, a substitution, and a translocation line of D. villosum chromosomes in a wheat background. Three races of P. striiformis and a β-glucuronidase-transformed strain of Pseudocercosporella herpotrichoides were used to inoculate plants and evaluate disease reactions. Of the 115 D. villosum accessions tested, 33 (28.6%) were resistant to one or more races of Puccinia striiformis and 8 accessions were resistant to all races. All 219 accessions of D. villosum tested were resistant to Pseudocercosporella herpotrichoides and 158 (72%) of the accessions had lower β-glucuronidase activity than the resistant wheat line VPM-1. Most of the accessions of D. villosum resistant to the stripe rust pathogen originated from Greece; however, there was no distinction among origins for resistance to the eyespot pathogen. Chromosome 4V was confirmed to carry the gene for resistance to P. herpotrichoides. At least one gene for resistance to Puccinia striiformis was located on the short arm of chromosome 6V of D. villosum in the 6VS/6AL-translocation line; this gene was named Yr26.

Quantitative genetic diversity and conservation strategies for an allogamous annual species, Dasypyrum villosum (L.) Candargy (Poaceae)

Dasypyrum villosum (L.) Candargy is a weedy annual diploid (2n = 14, VV genomes) allogamous grass species (Poaceae, Triticeae). Genetic variation for 12 traits was studied in 43 natural populations (31 from Italy and 12 from Croatia and Montenegro of former Yugoslavia) grown in a common field environment in California. Although 7 of 12 traits followed the theoretical prediction that a larger proportion of genetic variation was distributed within populations than among populations, exceptions were found for spike length, plant height, and days to flag-leaf emergence, heading, and anthesis. Covariate analysis showed that developmentally closely related characters were more likely correlated at both population and family within population levels. Geographically closer populations shared more genetic similarity than distant populations as indicated by mean coefficients of variation and cluster analysis of the Euclidean distances among populations. As few as five populations, each population with five or more half-sib seeds taken randomly from 5 plants, is expected to capture more than 95% of the total genetic variation of this species in the region sampled, but sampling a much larger number of seeds per population (> 1000) for long-term storage would supply research and plant breeding needs for several decades. If seed regeneration is required, populations can be sampled from clusters having similar genetic variation, and grown in reproductive isolation or bulked seed samples from all populations of each cluster group can be grown in isolation. The former is recommended if population integrity is desired while the latter is sufficient to provide genetic resources for plant-breeding purposes.

Isolation, characterization and application of a species-specific repeated sequence from Haynaldia villosa

A species-specific repeated sequence, pHvNAU62, was cloned from Haynaldia villosa, a wheat relative of great importance. It strongly hybridized to H. villosa, but not to wheat. In situ hybridization localized this sequence to six of seven H. villosa chromosome pairs in telomeric or sub-telomeric regions. Southern hybridization to whea-H. villosa addition lines showed that chromosomes 1V through 6V gave strong signals in ladders while chromosome 7V escaped detection. In addition to H. villosa, several Triticeae species were identified for a high abundance of the pHvNAU62 repeated sequence, among which Thinopyrum bassarabicum and Leymus racemosus produced the strongest signals. Sequence analysis indicated that the cloned fragment was 292 bp long, being AT rich (61%), and showed 67% homology of pSc7235, a rye repeated sequence. Isochizomer analysis suggested that the present repeated sequence was heavily methylated at the cytosine of the CpG dimer in the genome of H. villosa.It was also demonstrated that pHvNAU62 is useful in tagging the introduced 6VS chromosome arm, which confers a resistance gene to wheat powdery mildew, in the segregating generations.

Allelic diversity of high-molecular-weight glutenin protein subunits in natural populations of Dasypyrum villosum (L.) Candargy

Dasypyrum villosum (L.) Candargy (2n=14, V genome) is a wild, allogamous, diploid grass species that is a potential genetic resource for wheat improvement. The diversity of high-molecular-weight (HMW) glutenin subunits of the seed storage proteins of this species was examined in populations sampled in their natural habitats in Italy and Yugoslavia where the species is widely distributed. The results of selfed progeny tests confirmed that the allelic variation of HMW-glutenin subunits in D. villosum is controlled by a single locus (Glu-V1). Fourteen alleles at Glu-V1 were found among 982 individuals representing 12 populations from Italy and two from Yugoslavia, with a mean of seven alleles per population. Among the 14 Glu-V1 alleles, one produced no HMW-glutenin subunits, ten coded for a single subunit, and three for two subunits. The mobilities of all the subunits in SDS-PAGE gels were greater than that of reference subunit 7 of Triticum aestivum cv Chinese Spring. Eight of the alleles were relatively abundant (mean frequency over all populations ranged from 0.08 to 0.17) and distributed widely among the 14 populations (8 to 14); five of the alleles were rare (0.003 to 0.021) and found in only 1 to 5 populations. The frequencies of two alleles could not be individually estimated because of the similar electrophoretic mobility of their subunits. The multiple-allelic diversity at Glu-V1 was high (He ranged from 0.700 to 0.857) but similar from population to population. Overall, about 7% of the total allelic variation was distributed among populations (Gst=0.072), and more than 90% within populations. Whether the allelic variation at Glu-V1 is subject to natural selection is unknown, but the discovery of the homozygous null Glu-V1 alleles in the present study may be useful in pursuing this question. The multiple-allelic diversity in Glu-V1 presents the plant breeder with an opportunity to evaluate and select the most useful alleles for transfer to wheat. The importance of an evaluation genetic diversity in a wild species before interspecific gene transfers are attempted is well illustrated in this study.

Chromosomal location of seed storage protein genes in the genome ofDasypyrum villosum (L.) Candargy

Genes coding for glutenin-like subunits and for several prolamin subunits with electrophoretic mobilities (lactate-PAGE) corresponding to those of omega- and gamma-gliadins of wheat were located inDasypyrum villosum chromosome1V. Genes controlling four gliadinlike subunits with electrophoretic mobilities corresponding to those of alpha- and gamma-gliadins were located on the short arm of chromosome6V and on the long arm of chromosome4V. N-terminal amino acid sequences of these four components were also determined and homology with alpha-type gliadins was demonstrated. The presence of genes coding for glutenin- and gliadin-like subunits on chromosomes1V and6V demonstrates homoeology between theD. villosum chromosomes1V and6V and the chromosomes of homoeologous groups 1 and 6 in wheat. It is likely that the additional locusGli-V3 on chromosome4V originated by translocation from theGli-V2 locus.