Comparative cytogenetic analysis of Avena macrostachya and diploid C-genome Avena species Ekaterina D. Badaeva, Olga Yu. Shelukhina, Axel Diederichsen, Igor G. Loskutov, and Vitaly A. Pukhalskiy Abstract: The chromosome set of Avena macrostachya Balansa ex Coss. et Durieu was analyzed using C-banding and flu- orescence in situ hybridization with 5S and 18S-5.8S-26S rRNA gene probes, and the results were compared with the C- genome diploid Avena L. species. The location of major nucleolar organizer regions and 5S rDNA sites on different chro- mosomes confirmed the affiliation of A. macrostachya with the C-genome group. However, the symmetric karyotype, the absence of ‘‘diffuse heterochromatin’’, and the location of large C-band complexes in proximal chromosome regions pointed to an isolated position of A. macrostachya from other Avena species. Based on the distribution of rDNA loci on the C-genome chromosomes of diploid and polyploid Avena species, we propose a model of the chromosome alterations that occurred during the evolution of oat species. Key words: karyotypes, chromosome evolution, Avena, A. macrostachya, C genome, C-banding, FISH, rDNA. Re ´sume ´: Le jeu chromosomique chez l’Avena macrostachya Balansa ex Coss. et Durieu a e ´te ´ analyse ´ par coloration des bandes C et par hybridation in situ en fluorescence au moyen de sondes pour l’ARNr 5S et 18S-5,8S-26S. Les re ´sultats ont e ´te ´ compare ´s avec ceux du ge ´nome C chez les espe `ces diploı ¨des du genre Avena L. La localisation des principaux or- ganisateurs nucle ´olaires et des sites d’ADNr 5S sur les diffe ´rents chromosomes a confirme ´ la filiation de l’A. macrosta- chya avec le groupe a ` ge ´nome C. Cependant, le caryotype syme ´trique, l’absence d’« he ´te ´rochromatine diffuse » et la localisation des complexes de grandes bandes C au sein des re ´gions chromosomiques proximales sugge `rent que l’A. ma- crostachya occupe une position isole ´e par rapport aux autres espe `ces du genre Avena. Sur la base de la distribution des lo- cus d’ADNr sur les chromosomes du ge ´nome C chez les espe `ces diploı ¨des et polyploı ¨des du genre Avena, les auteurs proposent un mode `le pour les alte ´rations qui se seraient produites au cours de l’e ´volution des espe `ces d’avoine. Mots-cle ´s : caryotypes, e ´volution des chromosomes, Avena, A. macrostachya, ge ´nome C, coloration des bandes C, FISH, ADNr. [Traduit par la Re ´daction] Introduction Avena macrostachya Balansa ex Coss. et Durieu is a relict plant species endemic to the high altitudes of two northeast- ern Algerian mountain chains, the Aure `s and the Djurdjura (Baum and Rajhathy 1976; Guarino et al. 1991). It is the only perennial cross-pollinating species in the genus Avena L. Based on the analysis of phenotypic, developmental, and reproductive characters, A. macrostachya occupies an iso- lated position in the genus Avena (Baum 1977). At the same time, it is similar to the species of the genus Helictotrichon Besser ex Roem. et Schult. in its perenniality, mode of prop- agation, and some cytogenetic characteristics (Guarino et al. 1991; Winterfeld et al. 2009). Nevertheless, A. macrostachya is regarded as a true Avena species (Baum and Rajhathy 1976). Its perennial nature, extreme winter hardiness, and resist- ance to powdery mildew, crown and stem rust, barley yel- low dwarf mosaic virus, soil-borne mosaic virus, and the aphid Rhopalosiphum padi (Leggett 1987; Hoppe and Pohler 1988; Weibull 1988; Santos et al. 2002; Jellen and Leggett 2006; Yu and Herrmann 2006) make A. macrostachya a pro- Received 19 August 2009. Accepted 10 November 2009. Published on the NRC Research Press Web site at genome.nrc.ca on 22 January 2010. Corresponding Editor: G. Scoles. E.D. Badaeva. 1 Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 32 Vavilov Street, Moscow 119991, Russia. O.Yu. Shelukhina and V.A. Pukhalskiy. N.I. Vavilov Institute of General Genetics, Russian Academy of Sciences, 3 Gubkin Street, Moscow 119991, Russia. A. Diederichsen. Plant Gene Resources of Canada, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada. I.G. Loskutov. N.I. Vavilov Institute of Plant Industry, Russian Academy of Agricultural Sciences, 44 Bolshaya Morskaya Street, St. Petersburg, Russia. 1 Corresponding author (e-mail: K_Badaeva@mail.ru). 125 Genome 53: 125–137 (2010) doi:10.1139/G09-089 Published by NRC Research Press