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ISHS Acta Horticulturae 1133: XI International Rubus and Ribes Symposium

Rubus ploidy assessment

Authors:   K.E. Hummer, N.V. Bassil, L.A. Alice
Keywords:   genetic resources, plant breeding, flow cytometry, ploidy
DOI:   10.17660/ActaHortic.2016.1133.13
Abstract:
The US Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository (NCGR), Corvallis, Oregon, maintains the national collection for Rubus germplasm. The NCGR genebank includes more than 2,035 Rubus accessions, with representatives of 174 Rubus taxa from 57 countries. The primary collection of clonal Rubus and their wild relatives are maintained as plants in containers in greenhouses and screenhouses. The main crops of global economic importance include red raspberries (R. idaeus), the artificial subgenus Idaeobatus, and blackberries, subgenus Rubus, and hybrids between them. Breeders wish to expand gene accessibility outside these subgenera to include representatives of the rich diversity and variability present in the genus. The objective of this research was to evaluate ploidy levels of recently acquired Rubus accessions added to the NCGR collection. Ploidy was assessed through flow cytometry using cell preparations from leaf samples. The base chromosome number for Rubus is x=7. We evaluated Rubus species from seven subgenera. Subgenus Cylactis had a 4x member; subgenus Dalibarda had a diploid member, and subgenus Idaeobatus had 2x, 3x, and 4x types. The blackberry accessions, subgenus Rubus, were the most diverse, having 2x, 4x, 5x, 6x, 7x, 8x, 10x, and 12x cytotypes. Some R. armeniacus samples, introduced from Europe but naturalized in Oregon and California, were 4x; others unexpectedly had much higher ploidy levels. This suggests that R. armeniacus has hybridized with native species of higher ploidy. The two species of Micranthobatus examined were 4x confirming previous chromosome counts, but had very small genomes. Further study of other species in this subgenus is warranted.

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