A 6kb rDNA probe comprising the 18S coding plusspacer sequences has been hybridized to the metaphase chromosomes of apple rootstock cultivar MM106 demon-strating the localization of ribosomal gene arrays in the vicinity of the telomeric regions of the short arms of chro-mosomes 6 and 14. The in situ results using digoxygenin labelling coupled to an alkaline phosphatase immunoassay were confirmed by silver staining for NORs and nucleoli. This study demonstrates the feasibility of molecular cyto-genetic analysis of very small chromosomes (1.0-2.7μm)of apple.
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