The rooting ability of in-vitro shoot cultures established from a UK collection of the common ash (Fraxinus excelsior L.) and their ex-vitro survival

There is renewed in the tissue culture of the European ash in response to ash dieback disease. Shoot cultures were established for 135 clones from 13 ash mother trees from the UK’s national collection, on DKW medium with 3ppm of BAP. Most were generated from hypocotyl pieces excised from sterile germinating mature ash seeds. Another 24 clones were lost to bacterial contamination, which was identified as Bacillus megaterium or possibly a close relative. These cultures were disposed of as it was difficult to eliminate the bacterium from them. The ability of all of the cultures to produce rooted plants capable of normal growth under nursery conditions was tested by exposing excised shoots to DKW medium with 3ppm IBA for 2 weeks, followed by 4–6 weeks on hormone-free medium. Across all experiments 41.5% of uncontaminated plants and 11.6% of contaminated plants produced roots in-vitro. Although differences were observed in the rooting ability between clones, families and from trial to trial, the only significant effect was whether the shoots were contaminated or not. In addition, 92.6% of the uncontaminated plants survived the transfer to the nursery as opposed to 62.1% of the contaminated plants. We show here that a single methodology can be successfully used to produce large numbers of clonal ash plants on demand from a wide cross-section of the UK’s ash breeding population, although contamination issues will need to be closely monitored for this approach to be used as part of the strategy for combating overcoming ash dieback disease.