THE CLOSE RELATIONSHIP BETWEEN THE A-GENOME AND B-GENOME IN AVENA-L (POACEAE) DETERMINED BY MOLECULAR CYTOGENETIC ANALYSIS OF TOTAL GENOMIC, TANDEMLY AND DISPERSED REPETITIVE DNA-SEQUENCES

The genus Avena L. (Poaceae) consists of diploid, tetraploid, and hexa ploid species, with the B genome known only in tetraploid species and the D genome in the hexaploid species. DNA:DNA in situ hybridization, using total genomic DNA from diploid Avena strigosa Schreb. (A, genome ) as a probe, labelled all 28 chromosomes of the AB tetraploid Avena v aviloviana (Malt.) Mordv. strongly and uniformly, revealing the close relationship between these two genomes. Comparison of patterns of size -separated DNA restriction fragments between the diploid A. strigosa a nd the tetraploid A. vaviloviana, using 32 different restriction enzym es, revealed no differences. Southern hybridization using total AB gen omic DNA as a probe also gave no differences in banding patterns betwe en the two genomes, even when a large excess of A genomic DNA was used as a block. From an A. vaviloviana genomic library, 1800 colonies wer e blotted and probed sequentially with A and AB genomic DNA, but no co lony was identified to be B genome specific. DNA digests of AB genome tetraploids with restriction enzyme HaeIII gave a strong band at 4.2 k b. Clone pAbKB3, derived from the 4.2 kb band, was found to be part of a Tyl-copia-like retrotransposon present in A and B genome chromosome s. Cloned rRNA genes were used for in situ hybridization and showed th at diploid A. strigosa has four major sites for 18S-25S rDNA and two p airs of sites for 5S rDNA (pairs on the same satellited chromosome, on different chromosome arms), while 4x A. vaviloviana has eight major s ites for 18S-25S rDNA and four pairs of sites for 5S rDNA (pairs on th e same satellited chromosome, on different chromosome arms). A repetit ive sequence from rye pSc119.2, showed dispersed hybridization, while the telomeric sequence in clone pLT11 hybridized to telomeres. Again n o discrimination was possible between A and B genome chromosomes. The molecular similarities between the diploid A. strigosa and the barbata group tetraploids clearly indicate that the barbata group of tetraplo ids arose from A(s) diploids through autotetraploidization. (C) 1997 A nnals of Botany Company.