Ploidy Levels and Genome Sizes of Berberis L. and Mahonia Nutt. Species, Hybrids, and Cultivars

Abstract

An extensive survey of genome sizes and ploidy levels was conducted for a diverse collection of Berberis and Mahonia taxa (Berberidaceae). Propidium iodide flow cytometric analysis was conducted using Pisum sativum L. ‘Ctirad’ (2C DNA = 8.76 pg) as an internal standard to determine genome sizes. Mean 1CX genome sizes varied between the two Mahonia subgenera (Occidentales = 1.17 ± 0.02, Orientales = 1.27 ± 0.01), whereas those of Berberis subgenera were similar (Australes = 1.45 ± 0.03, Septentrionales = 1.47 ± 0.02) and each significantly larger than those of Mahonia. Traditional cytology was performed on representative species to calibrate genome sizes with ploidy levels. Polyploidy among both wild and cultivated taxa was found to be rare. Although the majority of species were determined to be diploid with 2n = 2x = 28, artificially induced autopolyploid Berberis thunbergii seedlings were confirmed to be tetraploid and an accession of Mahonia nervosa was confirmed to be hexaploid. Genome size and ploidy level reports for the majority of taxa sampled are presented for the first time and are intended to be of use to plant breeders, ecologists, and systematists.