CLOSELY-RELATED ALLIUM SPECIES (ALLIACEAE) SHARE A VERY SIMILAR SATELLITE SEQUENCE

A satellite sequence repeat of Allium cepa was tested by fluorescent i n situ hybridization (FISH) for cross-hybridization to chromosomes of 27 species (in 37 accessions) belonging to 14 sections of four subgene ra of Allium. All investigated species of sect. Cepa, With the two sub sects. Cepa and Phyllodolon, revealed clear satellite-specific hybridi zation signals mainly at their chromosome termini. The tested species belonging to other sections/subgenera revealed no hybridization signal s. An exception was A. roylei, assigned to sect. Oreiprason. Its chrom osomes also showed strong terminal hybridization signals. This and oth er features suggest a close relationship of A. roylei to the species o f sect. Cepa in spite of deviating morphological characters. The diver gence between the satellite repeats to species to which the A. cepa re peat cross-hybridized was determined and revealed high degrees of simi larity. Therefore, we conclude that this satellite sequence had evolve d already in progenitor forms of sect. Cepa and remained unusually wel l conserved during speciation. This might indicate selection pressure exerted on a secondarily acquired telomere function of the satellite s equence.