Evaluation of Genetic Variation Among Native Pawpaw Patches at the Environmental Education Center at Kentucky State University

Pawpaw [Asimina triloba (L.) Dunal] is a tree-fruit that is a native understory tree in the eastern region of the United States. This native tree species is in the early stages of domestication and fruit is being sold at farmers’ markets, community supported agriculture, and gourmet restaurants. Pawpaws also contain Annonaceous acetogenins in the twigs and fruit which have anticancer and antiviral properties with many new product applications. Wild Pawpaw patches are usually found in the forest understory and produce many root suckers, presumably forming large clonal patches, thus contributing to poor fruit set within a patch due to flower self-incompatibility.

As part of KSU’s role as the USDA National Clonal Germplasm Repository for Pawpaw, assessing genetic diversity displayed in this species, determining the role clonality plays in patch adaption and survival, and collecting unique germplasm for our repository orchards are important research priorities. Native patches serve an important role in the ecosystems around streams and rivers in terms of fruit production for animals, soil erosion control, and enhancing insect biodiversity. The zebra swallowtail butterfly larvae feed exclusively on young Pawpaw foliage. Unique native Pawpaw germplasm could also serve as future cultivars for growers or be used in KSU breeding efforts. The understory niche occupied by Pawpaw may also prevent the establishment of invasive plant species (such as honeysuckle bush).

How Pawpaw patches have spread in this region is poorly understood. Native Americans may have spread seed to promote fruit production. Animals may consume fruit and spread seed in scat. Viable Pawpaw seeds are buoyant and can float down streams to form new patches. Clonal patches can develop through root suckering. The objective of this study was to determine if DNA fingerprinting of patches at the KSU Environmental Education Center in Henry County, Kentucky near a stream would suggest if root suckering (clonal patches) or water transport of seeds (many genotypes) were mechanisms of patch establishment. DNA was extracted using the DNAMITE Plant Kit from leaf samples collected from 20 trees per patch on a transect line in three native patches at the EEC. Patch 1 was located on a hill, while patches 2 (downstream) and 3 (upstream) were located on a stream about 100 feet apart. Primers B3, B103, B129, C104, and G119 were used to amplify SSR products, and products were separated with a 3130 Applied Biosystems capillary electrophoresis system.

All three patches were genetically distinct, with patches 2 and 3 being more similar (Figs 1 and 2). Patch 3 was clonal with only one genotype. The high genetic variation in patch 2 supports involvement of water transport of seed from patch 3 in the establishment of the patch; however, animal transport of seed could also have led to patch establishment.

Fig. 1. EEC Pawpaw patch 2 showing at least 3 genotypes.

 

Fig. 2. Genetic variation and relatedness of the three EEC Pawpaw patches

This project was supported by USDA-McIntire-Stennis Funding (project KYX-90-09-1).