Assessment of Genetic Diversity of Pawpaw (Asimina triloba) Cultivars with Simple Sequence Repeat Markers

The pawpaw [Asimina triloba (L.) Dunal.] is a tree fruit native to the Southeastern and Midwestern United States which is in the beginning stages of commercial production. In 1994, Kentucky State University (KSU) was designated as a satellite repository for Asimina preservation in the U.S. Department of Agriculture, National Plant Germplasm System. Germplasm evaluation, preservation, and dissemination have been a high priority at KSU since that time. Cultivar loss since the beginning of the early twentieth century may have eroded the genetic diversity of commercially available selections. The objectives of this study were to develop simple sequence repeat (SSR) primers for pawpaw and to use SSR markers to assess genetic diversity in 41 pawpaw cultivars and advanced selections from the PawPaw Foundation (PPF) breeding program. Leaf samples were collected from the cultivars BH10, Cales Creek, Davis, Gordon, Greenriver Belle, IXL, Middletown, Mitchell, NC-1, Overleese, PA-Golden1, PA-Golden3, PA-Golden4, Potomac, Prolific, Rappahannock, Rebecca’s Gold, Shenandoah, Sue, Sunflower, Susquehanna, Sweet Alice, Taylor, Taytwo, Wabash, Wells, Wilson, and Zimmerman, as well as 13 advanced selections from PPF.  DNA was extracted from the leaves using the DNAMITE Plant Kit. Four SSR primer sets B3, B103, B129, and G119 were labeled with FAM and used to amplify SSR-PCR products. These products were then separated using a 3130 Applied Biosystems capillary electrophoresis system. Each primer yielded approximately 10 alleles for each primer combination. Genetic relationships among the pawpaw cultivars and advanced selections showed significant genetic variation suggesting that the genetic base of currently available cultivars is diverse.