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The genus Avena is organized into 14 taxa, each representing a biological species (8 diploid, 5 tetraploid, and 1 hexaploid taxa) classified on the basis of chromosome number, genome, diaspore (unit of dispersal), flower morphology, and cross fertility (Ladizinsky 1989). Based on chromosome pairing and structure, diploid, tetraploid and hexaploid species were given the genomic designations A or C, AABB or AACC, and AACCDD, respectively (Rajhathy and Thomas 1974). The primary cultivated oat species are hexaploid (2n = 6x = 42) A. sativa L. and A. byzantina C. Koch. Extensive cytological work has led to the development of karyotypes, as well as aneuploid stocks (Rajhathy and Thomas 1974; Hacker and Riley 1965; Morikawa 1985; Linares et al. 1992; Jellen et al. 1993a, b). However, identification of homoeologous groupings in hexaploid oat has been hindered by the lack of a complete aneuploid series, useful genetic markers, and easily identifiable chromosome morphology. The C-banding technique, and in certain cases the use of semi-automated digital image analysis/enhancement systems (Jellen et al. 1993a), has greatly facilitated the discrimination of individual chromosomes and/or genomes in diploid (Yen and Filion 1977; Fominayaetal. 1988a), tetraploid (Fominaya et al. 1988b) and hexaploid species (Linares et al. 1992; Jellen et al. 1993a). For instance, the C genome chromosomes are easily distinguished on the basis of their dark staining pattern from the A, B or D genome chromosomes (Fominaya et al. 1988; Jellen 1992). |
