Ploidy and genome-size variation in Loropetalum chinense accessions cultivated in the US

Abstract Loropetalum chinense and L. chinense var. rubrum are popular ornamental shrubs known for their distinctive flowers and foliage color. Due to its wide adaptability, Loropetalum has been widely used in the U.S. nursery market for various landscaping purposes. However, the limited understanding of genetic diversity among Loropetalum accessions presents challenges for breeding efforts. This study investigated the relative genome sizes and ploidy levels of Loropetalum accessions in the U.S. to contribute to future breeding strategies. Flow cytometry was used to determine genome size and estimated ploidy, and chromosome counts were performed to validate ploidy estimates. As a result, 53 were identified as diploids, and 1 as a triploid. The 1Cx genome size across all accessions ranged from 2.43 to 3.21 pg, with an average of 2.72 pg. The stomata size of the triploid cultivar ‘Kurenai Daiou’ Jazz Hands Bold® was significantly larger, and the stomatal density was significantly lower than that of the three tested diploid cultivars. The pollen morphology shows that the triploid cultivar pollen is undeveloped, and the diploid cultivar pollen is fully developed. These results provide a foundational understanding of ploidy and genome size variation in L. chinense germplasm, which will benefit future Loropetalum breeding efforts.