Article (magazine) published 2023.

Roses (Rosa spp. L.) are valuable horticultural crops with global production, markets, and utilization. Cytogenetics of roses can be complicated with variation in ploidy among species and hybrids and occurrence of unreduced gametes, unbalanced (canina) meiosis, and aneuploidy. Most modern rose cultivars are complex, interspecific hybrids with unknown ploidy. Despite most breeding efforts being focused on crossing cultivated varieties, the genome size information is often only available at the generalized species level. The goal of this study was to survey cultivars and breeding lines to determine relative genome sizes and ploidy levels. Flow cytometry was used to determine relative genome size and ploidy levels of 174 accessions of shrub, hybrid tea, grandiflora, floribunda, polyantha, R. chinensis, and R. rugosa cultivars and breeding lines. Chromosome counts were performed to calibrate relative genome size to ploidy level and confirm previously published ploidy reports. 1Cx relative genome size ranged from 0.46 to 0.64 pg and the 2C relative genome size ranged from 0.96 pg to 1.28 pg for diploids, 1.38 to 1.86 pg for triploids, and 1.87 to 2.50 pg for tetraploids when using DAPI fluorochrome and Pisum sativum 'Ctirad' as the internal standard. Chromosome counts further substantiated these ranges and confirmed ploidy of cultivars that were in disagreement with earlier reports for three cultivars. These results provide an extensive database of genome sizes and ploidy for diverse cultivars and breeding lines of rose and establish/validate flow cytometry methods for future applications