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Wenhao Dai and Victoria Jacques

Periwinkle, a perennial commonly used as a summer bedding plant, is known as the source of vinca alkaloids used to treat lymphocytic leukemia and Hodgkin's disease. It is also one of the natural hosts of many phytoplasma diseases, such as X-disease of major Prunus species, aster yellows, and ash yellows diseases. Therefore, periwinkle is an ideal plant species for phytoplasma disease research, such as disease transmission, species resistance, and resistant gene screening. Periwinkle tissue culture was established by incubating sterile seeds in hormone-free Murashige and Skoog (MS) medium. Plants were successfully regenerated from in vitro leaf tissues of periwinkle. Adventitious shoots were induced when leaf tissues were cultured on Murashige and Skoog (MS) medium or woody plant medium (WPM) supplemented with benzyladenine (BA) and naphthaleneacetic acid (NAA). Nearly 75% of leaf explants produced shoots in both media with 10–20 μm BA and 1 μm NAA. A mean of 4.3 shoots was produced from each explant cultured on WPM, whereas only 2 shoots were produced on MS medium under 16-h photoperiod. Leaf explants under dark treatment for 2 weeks produced big callus only, indicating that light is necessary for shoot formation. Most adventitious shoots were induced from the joint of leaf blade and petiole. In vitro shoots (>1.5 cm) were easily rooted in half-strength MS medium. Addition of NAA dramatically increased root number, with more than 20 roots being induced in 5 μm NAA medium. Rooted plants were transferred to potting medium and grown in a greenhouse.

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Wenhao Dai*, Christopher P. Johnson, Victoria A. Jacques and James A. Walla

An Agrobacterium-mediated transformation system was developed for chokecherry (Prunus virginiana L.), one of the most popular native small tree or large shrub species for resource conservation and wildlife habitat in North America. Leaf tissues from in vitro plants previously maintained in MS medium with 2.5 μm BA were co-cultivated on woody plant medium (WPM) containing 10 μm BA and 200 μm acetosyringone with Agrobacterium tumefaciens strain EHA105 harboring the binary Ti plasmid pBI121 carrying the uid A gene encoding for β-glucuronidase (GUS) and the npt II gene encoding neomycin phosphotransferase II. Infected leaf explants were disinfected in sterile water and antibiotics and then transferred to WPM containing 10 μM BA and the antibiotics cefotaxime, carbenicillin, and kanamycin (CCK) for shoot regeneration at 25 °C with a 16-hour photoperiod. Agrobacterium concentration, pre-conditioning of explants, application of acetosyringone, infection time, and kanamycin tolerance of leaf tissues were evaluated for effects on transformation efficiency. Regeneration of chokecherry shoots on kanamycin-containing medium and screening by GUS histochemical assays showed that both the npt II and the uid A genes were successfully transferred into chokecherry. The transformation will be further confirmed by polymerase chain reaction (PCR) and Southern blot analyses.