EVIDENCE FOR SEVERAL GENOMES IN HELIANTHUS

Forty taxa belonging to 36 species and four unclassified accessions of Helianthus were studied using RAPD technology. Single ten-mer primers were screened for those amplifying fragments common to several specie s. We found that when several species shared a common fragment, they b elong to the same section of the genus. Moreover, we also found that s ome fragments are common to all species of the Helianthus. Most of the fragments were found to be of the same size in these species and to s hare the homology indicated by molecular hybridization. Out of 118 ret ained fragments, 33 were common to all Helianthus species, 56 were uni que to perennial species of sects. Atrorubentes and Ciliares, 24 were unique to sect. Atrorubentes, 29 were unique to sect. Helianthus, wher eas 0 were unique to sect. Ciliares. Each set of common or specific fr agments was assumed to belong to a genome: (1) the C genome carrying t he fragments common to all species of the three sections, (2) the H ge nome unique to sect. Helianthus, (3) the P genome common to perennial species (sects. Atrorubentes and Ciliares), and (4) the A genome uniqu e to sect. Atrorubentes. The genomic structure was therefore HC for se ct. Helianthus, CPA for sect. Atrorubentes, and CP? for sect. Ciliares . Molecular hybridizations with amplification products revealed homolo gies between Helianthus genomes and several other genera in the Helian thinae sub-tribe. The simple method used to characterize these fragmen ts led to powerful tools for recognizing genomes which reconcile the s ection organization of the genus and the degree of difficulty in cross ing perennial and annual forms.