Abscisic acid induced dormancy and hardening of in vitro Saskatoon berry (Amelanchier alnifolia Nutt.)
Baldwin, Brian D.
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In vitro plantlets of Amelanchier alnifolia Nutt. 'Smoky' showed inhibited bud break in response to ABA application to tissue culture growing medium, but did not demonstrate a condition of innate dormancy. Partial formation of terminal buds, and axillary bud transition in phenotype from summer to winter form was produced by inclusion of 50 µM ABA in tissue culture growing medium when BA levels were decreased from 11.0µM to 5.5µM and NAA was eliminated. Addition of 50µM ABA to growing medium approximately doubled the -5°C hardiness levels of control plantlets, but ABA application alone did not generate hardiness levels as high as those seen during low temperature/short day (4°C/8h) acclimation (-27°C). Addition of BA to medium significantly reduced the efficacy of ABA-induced freezing tolerance. Wounding of plantlets during subculture was found to produce a rapid but transitory increase in hardiness level from -5°C to -9°C within 24 hours of subculture. Newlysubcultured plantlets were found to increase in hardiness more rapidly, and to a greater extent than reports previously published for these plantlets in culture. While short days (8h) slightly enhanced freezing survival of plantlets under both warm (23°C) and cool (4°C) temperatures, a pre-treatment of short warm days did not increase the rate of plantlet hardening under cold inductive conditions. Buds collected from orchard-grown plants demonstrated rising innate dormancy levels in late summer, with maximum levels between early September and late November. From December to the time of natural spring bud break, innate inhibition levels steadily decreased. Similar buds placed in culture were induced to grow at all seasons on BAsupplemented medium and were inhibited on ABA medium. On hormone-free medium, growth responses of de-scaled buds supported on stems above the medium were most similar to the dormancy profile of buds generated outside of culture conditions.