Pilot Study of Genetic Diversity and Structure in Elite Germplasm of Hibiscus syriacus

Rose of Sharon (Hibiscus syriacus L.) is an important perennial deciduous ornamental plant, featured by the daily flowering habit and a prolonged flowering period. However, the genetic relationships of the elite germplasmare largely unclear, which hampers the breeding programs of H. syriacus. Here, we analyzed the genetic diversity andstructure of 46 cultivars by employing a combination of 10 simple sequence repeat (SSR) and 5 inter-simple sequence repeat (ISSR) polymorphicmarkers. On average, 1.251 effective alleles per locus were detected for the SSR markers, in contrast to 1.321 for ISSR. Consistently, these elite accessions were grouped into five clades when using either marker or a combination of both, albeit with some differences. In the combined topology, clade II contains three relatively less multiple-petaled accessions, "Notwoodone" and its branch mutant "Bricutts", as well as H. syriacus var. Shigyoku. By contrast, "Duc de Brabant" and "Mindour1" are both pink multiple-petaled accessions in clade III, in addition to a solo single-petaled "Oiseau Bleu" in clade I. Clade V was the largest group of 34 accessions, which account for 73.9% of the evaluated Hibiscus varieties and cluster into six subclasses. Overall, these varieties have some morphological variances in both patterns and colors of flowers. They show similarities in subclass scale, as exemplified by "Lady Stanley" and its branch mutant, "America Irene Scott". The distantly related varieties, like in clade I and clade V, would benefit for breeding new varieties of high-hybrid vigor. Together, we updated a pilot study of the genetic diversity andstructure in elite varieties of H. syriacus, which could provide new insights into marker-assisted selection and genetic breeding of new varieties.