THE GENOME SIZES OF HORDEUM SPECIES SHOW CONSIDERABLE VARIATION

Hordeum, distributed worldwide in temperate zones, is the second large st genus in the tribe Triticeae and includes diploid, tetraploid, and hexaploid species. We determined, by DAPI staining and flow cytometry, the nuclear DNA content for 35 accessions of the genus Hordeum, from a total of 19 species, including specimens of 2 cultivars and 2 landra ces of Hordeum vulgare ssp. vulgare as well as samples of 12 Hordeum v ulgare ssp, spontaneum populations. Genome sizes ranged from 5.69 to 9 .41 pg for the G(1) nuclei of the diploids, and from 13.13 to 18.36 pg for those of the tetraploids. This constitutes a 1.7-fold variation f or the diploids, contrasting with a 4% variation previously reported. For H. vulgare ssp. vulgare (barley), the accessions examined differed by 18%. These variations in genome size cannot be correlated with mei otic pairing groups (I, H, X, Y) or with proposed phylogenetic relatio nships within the genus. Genome size variation between barley accessio ns cannot be related to status as cultivated or wild, or to climatic o r geological gradients. We suggest these data may indicate rapid but s poradic changes in genome size within the genus.