GENOMIC RELATIONSHIPS BETWEEN DASYPYRUM-VILLOSUM (L) CANDARGY AND DASYPYRUM-HORDEACEUM (COSSON ET DURIEU) CANDARGY

The origin and genomic constitution of the tetraploid perennial specie s Dasypyrum hordeaceum (2n = 4x = 28) and its phylogenetic relationshi ps with the annual diploid Dasypyrum villosum (2n = 2x = 14) have been investigated by comparing the two genomes using different methods. Th ere is no apparent homology between the conventional or Giemsa C-bande d karyotypes of the two Dasypyrum species, nor can the karyotype of D. hordeaceum be split up into two similar sets. Polymorphism within sev eral chromosome pairs was observed in both karyotypes. Cytophotometric determinations of the Feulgen-DNA absorptions showed that the genome size of D. hordeaceum was twice as large as that of D. villosum. Both the cross D. villosum X D. hordeaceum (crossability rate 12.1%) and th e reciprocal cross (crossability rate 50.7%) produced plump seeds. Onl y those from the former cross germinated, producing sterile plants wit h a phenotype that was intermediate between those of the parents. In t hese hybrids (2n = 21), an average of 13.77 chromosomes per cell paire d at meiotic metaphase I. Trivalents were only rarely observed. Throug h dot-blot hybridizations, a highly repeated DNA sequence of D. villos um was found not to be represented in the genome of D. hordeaceum. By contrast, very similar restriction patterns were observed when a low-r epeated DNA sequence or different single-copy sequences of D. villosum or two sequences in the plastidial DNA of rice were hybridized to Sou thern blots of the genomic DNAs of the two Dasypyrum species digested with different restriction endonucleases. By analyzing glutamic-oxaloa cetic-transaminase, superoxide dismutase, alcohol dehydrogenase, and e sterase isozyme systems, it was shown that both Dasypyrum species shar ed the same phenotypes, which differed from those found in hexaploid w heat. In situ hybridizations using DNA sequences encoding gliadins sho wed that these genes were located close to the centromere of three pai rs of D. villosum chromosomes and that they had the same locations in six pairs of D. hordeaceum chromosomes. We conclude that the autoploid origin of D. hordeaceum from D. villosum, which cannot be defended on the basis of chromosomal traits, is suggested by the other findings o btained by comparing the two genomes.