Flow cytometry was used to determine the ploidy levels in three subsets of the apple germplasm collection held by the USDA–ARS Plant Genetic Resources Unit. C-values ranging from diploid to pentaploid DNA content have been reported in the genus Malus, but cytogenetic information is often not available for specific trees. Diploid, triploid, and tetraploid clones were found in the core collection, a diverse group of Malus species and hybrids. Ploidy level may vary within and between Malus species in the wild. The progeny of 38 M. sieversii trees sampled from a natural population near Targabatai, Kazakstan were screened with flow cytometry. All the tested progeny had diploid C-values. Gigas characters such as larger leaves and fruit are sometimes associated with elevated ploidy levels. Ten elite scions of large-fruited M.sieversii were evaluated. All 10 had C-values in the diploid range. While flow cytometry of nuclei liberated from leaf tissue gave the expected DNA content for cultivars with previously known ploidy levels, this technique could not distinguish a known 2-2-4-4 periclinal chimera from diploid individuals.
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