Genet Resour Crop Evol (2008) 55:211–220 DOI 10.1007/s10722-007-9229-2 RESEARCH ARTICLE On evolutionary pathways of Avena species Igor G. Loskutov Received: 26 May 2006 / Accepted: 5 March 2007 / Published online: 13 June 2007 Ó Springer Science+Business Media B.V. 2007 Abstract This article presents literary review and morphogeographic data, taking into account the results analysis of evaluation of representative set of oat factors of heredity and variability, physiology and accessions of all Avena L. species. Results of complex biochemistry, cytogenetics and molecular biology. study of major morphological characters and utilization Many researchers have been studying various issues of the karyotype structure data confirmed by the results of evolution and geographical distribution of oat of RAPD and avenin spectrum analysis are presented. species over the continents and localization of Relationships of genomes of different Avena species at the areas of their origin and diversity (Vavilov each ploidy level are discussed. Two genomes form the 1926; Malzev 1930; Baum 1977; Baum et al. 1972; base of all Avena species, namely the A and C genomes. Baum et al. 1975; Coffman 1977). Domestication of Results of the evaluation of several characteristics of the different oat species and some of their forms, as oat species and their geographical distribution are derivatives of wild species, took place simulta- analysed. Probable evolutionary pathway of Avena neously and independently in some regions species are suggested. Most likely the centres of origin (Haussknecht 1899; Thellung 1911; Trabut 1914; of genus Avena L. are determined. Malzev 1930; Mordvinkina 1936). Identifying the foci of morphogenesis both for the cultivated Keywords Avena species Á Centres of origin and species and their wild progenitors is a subject of diversity Á Evolution Á Genomes Á Geographical contemporary investigations. Very interesting from distribution the evolutionary point of view are cytogenetical and molecular biological analyses of plant forms and interspecific hybrids by modern methods. They have Introduction helped to find answers to a number of questions related to the phylogeny of oat species, clarify the Evolutionary research is aimed to perceive degree of relationship between them and identify interactions between species on the basis of their genomic composition (Malzev 1930; Loskutov 2001b). I. G. Loskutov (&) Department of Genetic Resources of Oat, Barley, Literature review Rye, N.I. Vavilov Institute of Plant Industry, 44, Bolshaya Morskaya Street, St Petersburg 190000, Russia Having analyzed volumes of factual data, it was e-mail: [email protected] concluded that the A and C genomes characterizing 123 212 Genet Resour Crop Evol (2008) 55:211–220 diploid species had originated by wide structural genome consists of two identical or very similar divergence from a genome of the progenitor of such (AA’) genomes (Fabijanski et al. 1990). It is assumed species. Minor variants (Cp, Cv and Al, Ad, Ac, As) that the weedy species A. barbata transferred to of each of those genomes were already obtained as a Ethiopia together with oat seeds was the source of the result of insignificant changes in a hypothetic tran- cultivated species A. abyssinica Hochst. which has sient form which had preceded the present-day been choking up oat fields until the present time species (Baum et al. 1973; Rajhathy and Thomas (Thomas 1995). On the other hand, species A. 1974; Holden 1979; Thomas 1995). The presence of a vaviloviana (Malz.) Mordv. and A. abyssinica strictly symmetrical karyotype confirms to the prim- Hochst. according to a number of morphological itiveness of the species within the group, while an characters according to Baum (1971) might be the asymmetrical karyotype distinguishes their heteroge- relics of the ancient African floras. neity and evolutional advancement (Levitskii 1931; Another group of species with the AC genome was Stebbins 1971). Thus, on the basis of the karyotype closely related to the hexaploid species. The origin of structure in the diploid species some researchers have A. magna Murph. et Fed. is supposed to be hybrid- assumed that the species with the A genome, ogenic, resulting from the contacts on the margins of possessing a symmetrical karyotype, are karyologi- the areas of distribution of diploid species (probably cally more primitive than those with the C genome A. canariensis Baum and A. ventricosa Balan.), and an asymmetrical karyotype (Leggett and Thomas which presumably caused the genesis of this allote- 1995). Meanwhile, the species with the C karyotype traploid. Some researchers were convinced by the are morphologically very primitive [according to results of interspecific crosses that the tetraploids Malzev 1930 such species have glumes very unequal, with the AC genome had originated from the diploid lower glume one-half of upper one, upper glumes species possessing such genomes: they are supposed with 5–7 veins, callus very long, awl shaped, about to be A. canariensis (Ac) and A. ventricosa (Cv) 10 mm in length], and therefore they belong to the (Rajhathy and Thomas 1974). group of species that underwent the process of Rajhathy and Thomas (1974) came to the conclu- evolution slowly. In the opinion of Stebbins (1971), sion that hexaploid forms had been brought to the species which demonstrate high karyotype asym- existence in the process of generic evolution by metry, but according to their morphological traits alloploid convergence of the species with the AC belong to ancient groups, are very likely archaic and genome and an unknown species with the D genome. have undergone the bradytelic type of evolution, The evolution of hexaploid species, closely linked although they are not really primitive. with diploid and tetraploid ones, is the most intricate According to Maltsev (1930), it is from the and complicated (Ladizinsky and Johnson 1972; primary centre of origin of all diploid oat species Rines et al. 1988). According to the data of Leggett the western part of the Mediterranean region (Atlas and Markland (1995a, b), A and D genomes are more Mountains/Pyrenees), where the greatest diversity of similar to each other and at the same time they are these forms is concentrated, the axes of modern areas expressly different from the C genome. The A of distribution of all 14-chromosome species radiate genome of the diploid progenitor could have obvi- to eastwards. ously been the donor of A and D genomes in Regarding the evolution of tetraploid oat species, hexaploid species (Linares et al. 1996). The latest it is possible to trace two main independent branches: data witness that the D genome is supposedly an the species with the AB genome and those with the unknown variant of the As–A’’ genome, similarly to AC genome. Genomic structure of the species with the B genome, but differing from the latter (Leggett the AB genome have most likely originated from the 1996, 1998). diploids with a variant of the As genome. There are Taking into account the karyotype structure, researchers who contend that Avena barbata Pott is cytogenetic features and interspecific hybridization an autotetraploid of one of the diploid species data, it is possible to conclude that the evolution of (Ladizinsky and Johnson 1972). The genome in A. the genus Avena L. obviously involved two different barbata could have been engendered by duplication genomes A and C, while all other genomes to a of chromosomes in one of the diploids, because this greater or lesser extent were derivatives from these 123 Genet Resour Crop Evol (2008) 55:211–220 213 forms. Supposing that according to the conventional the large-grain A. sterilis subsp. macrocarpa Briq. in scheme the diploid species A. canariensis (A the west. genome) and A. ventricosa (C genome) were the According to Thomas (1995), A. sterilis in its progenitors of the corresponding genomes, the northward movement generated fatua-type mutations evolved allopolyploids may have had structural that led to the emergence of A. fatua, from which changes in their chromosomes, which could have weedy forms of the cultivated hexaploid species A. caused their partial homology (Baum et al. 1973; sativa have evolved. Also here in South-Western Rajhathy 1966). Asia region was the place of origin of hexaploid According to the data of Coffman (1977), the naked forms which, according to opinion of some progenitor of the diversity of hexaploid forms was researcher, moved toward China (Holden 1979; A. sterilis L. originated in the Asiatic continent. Thomas 1995). This species most likely brought the cultivated As noticed by Vavilov (1926), the diversity of species A. byzantina C. Koch into existence, distribution areas attest to the fact that polyploids followed by a harmful weedy A. fatua L. that (tetraploids and hexaploids) generally proved to be inflicts cultivated crops. Deeper insight into the more enduring than diploids and more adapted to the evolutionary issues of hexaploid species has shown northern and alpine environments (A. fatua). that the study of translocations in oat chromosomes and correlations between geographic distribution of various forms using cluster analysis demonstrated Discussion of Avena evolution in view of recent high degree of genetic relationship between the studies of the VIR Avena collection accessions of A. byzantina and the forms of A. sterilis from the northern Mesopotamia, on the In the last decades, Avena L. Vavilov Institute of one hand, and the accessions of A. sativa L. and the Plant Industry (VIR) collection have been replenished forms of A. sterilis from the eastern Anatolia, on by new accessions and newly described species from the other (Zhou et al. 1999). Further examination all regions of the Mediterranean and Black sea of all hexaploid species helped to find out that regions. The global oat collection is represented by A. sativa L. is characterized by the presence of comprehensive specific and intraspecific diversity of translocations (97%) in contrast to A. byzantina both cultivated (10,000 accessions) and wild (2,000 (11%).