Repetitive DNA, genome and species relationships in Avena and Arrhenatherum (Poaceae)

Repetitive sequences have been widely used for examining genome and species relationships by in situ and Southern hybridization. In the present study, double-stranded DNA sequences, from denatured DNA reannealed to Cot = 1. from Avena strigosa (2n = 2x = 14; A genome; referred to as CotA) and Avena sativa (2n = 6x = 42; ACD genome; referred to as CotACD) were isolated with a hydroxyapatite column, and were used for in situ hybridization on hexaploid. A. sativa chromosomes. Probe CotACD labelled all chromosomes evenly throughout their length at the same intensity. Probe CotA labelled the 28 A and D genome chromosomes strongly and the 14 C genome chromosomes weakly. Three cloned repetitive sequences, pAvKB9 (126 bp), pAvKB26 (223 bp) and pAvKB32 (721 bp) were characterized in the A, B, C and D Avena genomes and the genus Arrhenatherum using molecular and cytological methods. Clones pAvKB9 and pAvKB26 were absent from the Avena C genome, while both could identify the presence of the D genome by Southern hybridization. In situ hybridization to diploid and tetraploid Avena species revealed that the probes showed a dispersed genomic organization and that they are present on both arms of all chromosomes. These sequences were excluded from areas where tandem repeats, such as rRNA genes and telomeres, are present. These results indicate the close relationship between A and D genomes and the presence of common DNA sequences between A and C Avena genomes. All three clones hybridized to Southern blots containing Arrhenatherum digested genomic DNA, indicating Arrhenatherum's close affinity to A, B and D Avena genomes. (C) 2000 Annals of Botany Company.