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Abstract
Kalmia latifolia L. (mountain laurel) is an outstanding flowering shrub and a promising ornamental native to the eastern U.S. To enhance its production and landscape performance in the southeastern U.S., plants having adaptability to southeastern environmental conditions are needed. Traditional breeding of woody plants takes 10-20 years, however it could be facilitated with aid of modern technologies. To efficiently breed and select mountain laurel for the southeast, we explored and collected germplasm in the U.S.; evaluated existing cultivars for container and landscape performance; assessed genetic relationship among taxa using ISSR; and improved seed germination using in vitro method. Fifteen wild populations were explored in Alabama, Florida, Georgia, Louisiana, Massachusetts, and South Carolina and collections were from 10 of them based on our breeding goals. A total of 277 plants was obtained from wild collection. From over 100 cultivars, 21 of them were selected for collection based on their desirable morphology and superior performance and 197 individual plants were obtained. In our evaluation, all cultivars yielded considerable growth in the first year of container trials and consistently performed well thereafter, indicating production of mountain laurel as a one-year container plant is feasible. Although most cultivars had difficulty establishing in southeastern landscapes, fall planting could improve establishment. Ostbo Red, Pristine, and Tinkerbell consistently excelled in field trials, indicating their greater adaptability to southeastern environmental conditions. Unique ISSR profile of each cultivar and clustering of related cultivars in UPGMA indicated accurate identification of cultivars and their pedigree can be achieved using ISSR. A low level of genetic diversity among populations was found while individuals within populations tended to be genetically different, illuminating the efficient means to increase diversity. A clear separation of cultivars and wild plants was observed, which might be due to the loss of genetic information during artificial breeding. Using in vitro seed germination protocol, seeds could be collected one month prior to full maturation and germinate in one month on WPM, which shortened the period from crossing to the seedling stage from 13-15 to 6 months and improved germination from 30% to over 90% compared with traditional method.