Total genomic DNA was isolated from study plants and was hybridized with 32P-labeled Allium fistulosum `Ishikura' genomic DNA; Southern blots were performed. Plant materials were Allium cepa `New Mexico Yellow Grano', the Allium fistulosum `Heshiko' and `Ishikura', and their F1 interspecific (Allium fistulosum × Allium cepa) hybrids. Sequences with high identity to the labeled DNA hybridized strongly (i.e., A. fistulosum `Ishikura' hybridized most strongly to itself, next with A. fistulosum `Heshiko'). The least hybridization was observed when A. fistulosum `Ishikura' was hybridized with A. cepa `New Mexico Yellow Grano'. Intensity of the signals observed when DNA of the F1 interspecific hybrids was probed with the `Ishikura' DNA was as expected, with the signals intermediate between those of A. fistulosum to A. fistulosum and A. fistulosum to A. cepa. A second study was performed to identify additional cytological markers in Allium. The 5srDNA and NOR genes from Triticum aestivum onto onion chromosomes using in situ hybridization. Evidence of hybridizations are the presence of fluorescing areas on the chromosomes.
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