2017 ASHS Annual Conference

Kalmia latifolia L. (mountain laurel) is an outstanding evergreen flowering shrub native to the eastern United States. Based on morphological traits and landscape performance, more than 100 mountain laurel cultivars have been released. Since morphological characteristics might vary greatly depending on growing conditions and could not reflect genetic relatedness, we examined genetic relationship among 24 popular cultivars using inter-simple sequence repeat (ISSR) markers. A total of 110 fragments were generated from 8 primers and 90 fragments (81.8%) were polymorphic. A genetic similarity matrix was established and a dendrogram was generated by UPGMA. Similarity coefficient values ranging from 0.5636 to 0.7909 indicated high degree of genetic variations between cultivars. The highest similarity was found between ‘Olympic Fire’ and its female parent ‘Ostbo Red’ that both have upright growth habit, red bud, and light pink corolla, while the lowest similarity was between ‘Freckles’ and ‘Kaleidoscope’ that also showed morphological variation. In the UPGMA tree, ‘Peppermint’ and ‘Pristine’ were distinct from others and tended to form a cluster. Other 22 cultivars exhibited two clusters. The first cluster consisted of 15 cultivars, among which ‘Snowdrift’ having medium green leaf and white bud showed genetic difference to other 14 cultivars having dark green leaf and pink or red bud. The second cluster included seven cultivars and was further divided into two subclusters. One subcluster comprised three dwarf and pink-budded cultivars (‘Elf’, ‘Minuet’, and ‘Tiddlywinks’) and another subcluster consisted of ‘Kaleidoscope’, ‘Pink Charm’, ‘Sarah’, and ‘Red Bandit’ that have purplish red stem and lanceolate leaf blade. The results will help in identification of mountain laurel cultivars and selection of parents for further breeding.