Pawpaw Cultivar Fingerprinting and Progeny Determination Using Simple Sequence Repeat Markers

The North American pawpaw [Asimina triloba (L.) Dunal] is a tree fruit native to areas in the eastern United States and is in the early stages of commercial production. Since 1994, Kentucky State University (KSU) has served as the USDA National Clonal Germplasm Repository, or gene bank, for pawpaw; therefore, germplasm collection and assessment are research priorities. Not only would DNA fingerprinting methods for pawpaw cultivars allow the authentication of clones currently being sold at nurseries, it would also allow the determination of the parentage of a number of advanced selections that are potentially the result of crosses attempted by the PawPaw foundation breeding effort. The objectives of this study were to develop simple sequence repeat (SSR) fingerprinting techniques with pawpaw cultivars and to determine if three advanced selections were truly progeny from a cross between the pawpaw selections 11-13 x 1-23. Leaf samples were collected from the pawpaw selections Taytwo, Sweet Alice, NC-1, 11-13, 1-23, and three progeny of 11-13 x 1-23. Leaf samples were also collected from a cherimoya (Annona cherimola) tree in the KSU greenhouse; cherimoya is in the same family as pawpaw. DNA was extracted from the leaves using the DNAMITE Plant Kit. Primers B3, B103, B118, B129, and G119 were labeled with 6-FAM and used to amplify SSR products. These products were then separated using a 3130 Applied Biosystems capillary electrophoresis system. All primers failed to amplify products in cherimoya; however, products were amplified by the SSR primers in the pawpaw selections examined and fingerprint patterns were useful in separating the genotypes. Unique allelic combinations using the primer set B103 indicated that two advanced selections thought to be progeny of a cross between the selections 11-13 x 1-23 are not actually the progeny from two parents. Pollen contamination during hand pollination or pollinator activity either before or after hand pollination resulted in seedlings that were not the result of a cross between 11-13 x 1-23.