Abstract:
Roses are the most economically important ornamental crop in North America with widespread use across multiple industries. Rosa hybrida represents a complex hybrid including about ten wild species. Much of the rose breeding conducted today relies on phenotypic selection and is subject to limitations including sterility in some cultivars, high heterozygosity, varying ploidy levels, and erratic seed germination. Tissue culture and genetic transformation is one method to directly introduce novel, valuable traits into elite rose cultivars. However, rose is a recalcitrant species in vitro, and cultivars exhibit a genotype-dependent response to culture conditions. In this study, we evaluated three rose cultivars, Italian Ice®, Carefree Beauty™, and Ringo All Star™ for their regeneration ability. We tested auxins, carbohydrates, and cytokinin sources to develop regeneration protocols for each cultivar. We also developed a foundation to transform Italian Ice® etiolated shoot meristems. Shoot meristems offer a few advantages to genetic transformation, including a shorter regeneration timeline post-transformation, and the potential ability to translate the procedure to other cultivars. This research has enhanced regeneration and transformation protocols for bioengineering these cultivars. Finally, we screened a diverse range of rose cultivars and breeding lines using flow cytometry to determine relative genome size and ploidy level. To calibrate relative genome size to ploidy and resolve disputing ploidy reports, cytology was performed on 8 cultivars. We confirmed the ploidy level of three cultivars whose previous ploidy reports disagreed with our flow cytometry data, including Knock Out®, one of the top selling landscape roses. This work has established flow cytometry as a valuable technique for identifying ploidy in rose and has also highlighted discrepancies with past reported ploidies of some cultivars.