AGRICULTURAL SCIENCES
Using Simple Sequence Repeat Markers to Distinguish Scion and Rootstock Tissues on Grafted Pawpaw
Trees
JEREMIAH D. LOWE*, KEIDRE LONG, and KIRK W. POMPER. Land Grant Program, Kentucky State
University, Atwood Research Facility, Frankfort, KY 40601-2355.
Pawpaw [Asimina triloba (L.) Dunal] is a tree fruit native to much of the Eastern United States that has
production potential in Kentucky. Pawpaw cultivars are routinely propagated by chip budding cultivar
scion wood onto seedling rootstocks. When chip budded trees are planted in orchards, adventitious shoots
often form on rootstock trunks and the scion shoot and adventitious rootstock shoots can be confused. It has
also been suggested that several pawpaw cultivars, such as Mitchell, have been switched with other
genotypes during propagation in nurseries. The objectives of this study were to determine whether
microsatellite markers unique to the pawpaw cultivar Mitchell could be identified and then used to
distinguish adventitious rootstock shoots from the Mitchell scion. Young leaves were collected from 30
pawpaw cultivars, including Mitchell, and from three trunk shoots (A, B, and C) from a Mitchell tree where
rootstock and scion shoots were indistinguishable. Genomic DNA was extracted from leaves using a
DNAmite Kit. SSR-PCR was carried out using primers B103 and B118 developed by Genetic Information
Services (Chatsworth, CA). Amplified products were separated via electrophoresis on 2.5% agarose gels
and stained with ethidium bromide and visualized with ultraviolet light. Both primers produced scorable
markers for the cultivar Mitchell and these markers indicated that branches A and B were identical to the
‘Mitchell’ control and that branch C was not, and was therefore a rootstock shoot. Microsatellite markers
provide a powerful tool for distinguishing scion and rootstock tissues on grafted pawpaw trees.