The process of crop domestication began 10,000 years ago in the transition of early humans from hunter/gatherers to pastoralists/farmers. Recent research has revealed the identity of some of the main genes responsible for domestication. Two of the major domestication events in barley were (i) the failure of the spike to disarticulate and (ii) the six-rowed spike. The former mutation increased grain yield by preventing grain loss after maturity, while the latter resulted in an up to 3-fold increase in yield potential. Here we provide an overview of the disarticulation systems and inflorescence characteristics, along with the genes underlying these traits, occurring in the Triticeae tribe.

The phylogenetic relationship between four basic genomes designated H, I, Xa, and Xu in the genus Hordeum was studied using a nuclear DNA sequence. The sequence, cMWG699, is single copy in the H. vulgare genome, and tightly linked to the vrs1 locus which controls two- and six-rowed spikes. DNA fragments homologous to cMWG699 were amplified from diploid Hordeum species and the nucleotide sequences were determined. A phylogeny based on both base substitutions and an insertion-deletion event showed that the H- and Xa-genome groups are positioned in one monophyletic group indicating that the Xa-genome taxa should be included in the H-genome group. The large H-genome group is highly homogeneous. The I and Xu genomes are distinctly separated from H and Xa, and form sister groups. Another phylogeny pattern based on data excluding the insertion-deletion gave a result that the Xa genome forms a sister group to the H-genome group. The difference between the H and Xa genomes was affected only by a single base insertion-deletion event, thus the H and Xa genomes are likely to be closely related. The I and Xu genomes were again distinctly separated from the H and Xa genomes.

The genus Hordeum consists of three cytotypes (2x, 4x, and 6x). Its reproductive isolation has been incomplete between closely related species and hence the genetic relationship is reticulate and complex. We used 32 taxa of Hordeum and three chloroplast DNA sequences, matK, atpB-rbcL, and trnL-trnF in the current study. Molecular phylogenetic analysis based on sequence data of the three chloroplast DNA regions clearly demonstrated genetic relationships among taxa and origin of polypoids. The formation of H. secalinum likely involved hybridization between Hordeum marinum subsp. marinum and a Eurasian diploid possessing the H genome. The formation of hexaploid Hordeum brachyantherum involved hybridization between tetraploid H. brachyantherum and diploid H. marinum subsp. gussoneanum. The formation of three tetraploids, H. brachyantherum, Hordeum jubatum, and Hordeum guatemalense, probably involved hybridization between H. brachyantherum subsp. californicum and an altered H genome diploid. The formation of Hordeum arizonicum involved the two taxa Hordeum pusillum and H. jubatum.

Genetic diversity of 33 Elymus caninus accessions was investigated using isozyme, RAPD, and microsatellite markers. The three assays differed in the amount of polymorphism detected. Microsatellites detected the highest polymorphism. Six microsatellite primer pairs generated a total of 74 polymorphic bands (alleles), with an average of 15.7 bands per primer pair. Three genetic similarity matrices were estimated based on band presence or absence. Genetic diversity trees (dendrograms) were derived from each marker technique, and compared using Mantel's test. The correlation coefficients were 0.204, 0.267, and 0.164 between isozyme and RAPD distance matrices, RAPD and microsatellite distance matrices, and between isozyme and microsatellite distance matrices, respectively. The three methodologies gave differing views of the amount of variation present but all showed a high level of genetic variation in E. caninus. The following points may be drawn from this study whether based on RAPD, microsatellite, or isozyme data: (i) The Icelandic populations are consistently revealed by the three dendrograms. The congruence of the discrimination of this accession group by RAPD, microsatellite, and isozyme markers suggests that geographic isolation strongly influenced the evolution of the populations; (ii) The degree of genetic variation within accessions was notably great; and (iii) The DNA-based markers will be the more useful ones in detecting genetic diversity in closely related accessions. In addition, a dendrogram, which took into account all fragments produced by isozymes, RAPDs, and microsatellites, reflected better the relationships than did dendrograms based on only one type of marker.

Genetic diversity of 33 Elymus caninus accessions was investigated using isozyme, RAPD, and microsatellite markers. The three assays differed in the amount of polymorphism detected. Microsatellites detected the highest polymorphism. Six microsatellite primer pairs generated a total of 74 polymorphic bands (alleles), with an average of 15.7 bands per primer pair. Three genetic similarity matrices were estimated based on band presence or absence. Genetic diversity trees (dendrograms) were derived from each marker technique, and compared using Mantel's test. The correlation coefficients were 0.204, 0.267, and 0.164 between isozyme and RAPD distance matrices, RAPD and microsatellite distance matrices, and between isozyme and microsatellite distance matrices, respectively. The three methodologies gave differing views of the amount of variation present but all showed a high level of genetic variation in E. caninus. The following points may be drawn from this study whether based on RAPD, microsatellite, or isozyme data: (i) The Icelandic populations are consistently revealed by the three dendrograms. The congruence of the discrimination of this accession group by RAPD, microsatellite, and isozyme markers suggests that geographic isolation strongly influenced the evolution of the populations; (ii) The degree of genetic variation within accessions was notably great; and (iii) The DNA-based markers will be the more useful ones in detecting genetic diversity in closely related accessions. In addition, a dendrogram, which took into account all fragments produced by isozymes, RAPDs, and microsatellites, reflected better the relationships than did dendrograms based on only one type of marker.

No abstract

The recombinant plasmid dpTa1 has an insert of relic wheat DNA that represents a family of tandemly organized DNA sequences with a monomeric length of approximately 340 bp. This insert was used to investigate the structural organization of this element in the genomes of 58 species within the tribe Triticeae and in 7 species representing other tribes of the Poaceae. The main characteristic of the genomic organization of dpTa1 is a classical ladder-type pattern which is typical for tandemly organized sequences. The dpTa1 sequence is present in all of the genomes of the Triticeae species examined and in 1 species from a closely related tribe (Bromus inermis, Bromeae). DNA from Hordelymus europaeus (Triticeae) did not hybridize under the standard conditions used in this study. Prolonged exposure was necessary to obtain a weak signal. Our data suggest that the dpTa1 family is quite old in evolutionary terms, probably more ancient than the tribe Triticeae. The dpTa1 sequence is more abundant in the D-genome of wheat than in other genomes in Triticeae. DNA from several species also have bands in addition to the tandem repeats. The dpTa1 sequence contains short direct and inverted subrepeats and is homologous to a tandemly repeated DNA sequence from Hordeum chilense.

An analysis of Amplification fragment polymorphism of DNA from 27 accessions of 19 tetraploid Elymus species was carried out using 18 wheat microsatellite (WMS) primer pairs and 10 decamer primers. Ten WMS primer pairs produced multiple polymorphism on all accessions tested. Two independent phenograms, one based on WMS-PCR and one on RAPDs, separated the 19 tetraploid species into two main groups, viz., the SH genome species group and the SY genome species group. The results coincide with the genomic classification of these species and hence support previous studies showing that Elymus is not a monophyletic genus. The assays indicated that accessions within a species cluster together, which concurs with the morphological classification. Interspecific and intraspecific polymorphisms were detected by the WMS-PCR and RAPD analyses. Variation was observed among accessions of Elymus caninus. The WMS-PCR detected a much higher level of polymorphism than the RAPD analysis. WMSs seem to be more efficient markers than RAPD markers for studying the population diversity of Elymus species. The potential of cross-species amplification of microsatellite markers as an additional source for genetic analysis and applications in Elymus is discussed in the context of these results.