Improved Regeneration of Wild Strawberry (Fragaria vesca) Using TDZ and 2,4-D

In order to facilitate the high throughput transformation required to use Fragaria vesca (wild strawberry) as a tool in genomic research, functional genomics, and gene discovery not only for strawberry but for fruit crops in general, we need to increase its regeneration frequency and transformation efficiency using Agrobacterium . Ten accessions of F. vesca representing a range of germplasm with worldwide distribution were obtained from the USDA National Germplasm Repository, Corvallis, Ore. for use in shoot regeneration experiments. Seed germination with or without vernalization ranged from 0% to 90%. In vitro growth varied for the accessions with five accessions eliminated from further experiments due to poor growth. In preliminary experiments with 125 leaf explants and 40 petiole explants combined representing PI 551573, PI 602923, and F. vesca `Alpine'; 100% of the uncontaminated explants regenerated at least one shoot after 8 weeks on medium supplemented with 1 mg·L -1 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea (thidiazuron or TDZ) and 0.2 mg·L -1 2,4-dichlorophenoxyacetic acid (2,4-D). In a replicated study of `Alpine' comparing regeneration on the above TDZ/2,4-D medium with control medium [0.25 mg·L -1 indole-3-butyric acid (IBA)/3 mg·L -1 benzyladenine (BA)], regeneration frequency at 6 weeks for leaf or petiole explants on control medium was 8% (n = 180) compared to 27% (n = 210) on the TDZ/2,4-D medium. This optimized shoot regeneration protocol for F. vesca `Alpine' is currently under investigation in transformation experiments with several other accessions and Agrobacterium constructs.