Diversity of chromosomal composition in top onion (Allium × proliferum (Moench) Schrad. ex Willd.) accessions from the VIR in vitro collection

Abstract

Background. Top onion, Allium × proliferum (Moench) Schrad. ex Willd., 1809 (2n=2x=16), is a species that is characterized by vegetative propagation by air or underground bulbs only. Accessions of this species have been shown to be hybrids of Allium cepa and Allium fistulosum (Fiskesjo, 1975; Vosa, 1976; Schubert et al., 1983; Puizina and Papes, 1999). Accessions of Allium × proliferum were obtained from various sources and conserved in the in vitro collection of VIR. However, their pedigree was unknown, therefore there was a need to determine the ploidy level and genomic composition of these accessions.Materials and Methods. Thirteen Allium × proliferum accessions from the VIR in vitro collection were studied. To characterize the ploidy level and genomic composition of the accessions, the research employed FISH with chromosome-specific markers (5S and 18S/25S rDNA) and GISH with differentially labeled DNA of the putative parent species, i.e., A. cepa and A. fistulosum.Results. According to GISH, all the studied accessions were hybrids of A. cepa and A. fistulosum. Most (10 out of 13) accessions were determined as diploid hybrids with eight A. cepa and eight A. fistulosum chromosomes. The accession К 3206 turned out to be a diploid 16-chromosome hybrid with eight A. cepa, seven A. fistulosum chromosomes and one rearranged chromosome. Accessions К 3205 and К 3202 were found to be polyploids. The A. × proliferum accession К 3202 contained seven A. cepa and 16 A. fistulosum chromosomes. The accession К 3205 is characterized by the presence of 16 chromosomes hybridizing with A. cepa DNA and 13 chromosomes hybridizing with A. fistulosum DNA. Only one chromosome of A. fistulosum in this accession was revealed to have a 5s rDNA locus.Conclusions. The above shows that the collection contains top onion accessions with karyotypic differences.