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

Abstract

Abstract Key message Shoot cultures from a population of British ash trees (Fraxinus excelsior L.) were assessed for their ability to form roots in vitro and to grow in nursery conditions. Most of the plants survived whether they had formed roots or not, but this was affected by a systemic contaminant. This information will be valuable for work aimed at overcoming ash die-back disease. Context Ash die-back disease is killing Europe’s ash trees, with much breeding and experimental work is underway to help overcome it, including this. Aims This work aimed to develop and test a set of standard tissue culture methods for propagating material from selected ash trees, and then to produce rooted clonal plants which could be transferred to nursery conditions. Methods Seed material from a range of British and Irish ash provenances were used for this work, with the shoot cultures being maintained on DKW based media, with 3 ppm BAP being added to induce shoot proliferation, with the shoots so generated being exposed to 3 ppm IBA to induce root formation in vitro. Results One hundred thirty-six shoot cultures were successfully established from 13 mother trees. Most were generated from hypocotyl pieces excised from sterile germinating ash seeds on DKW medium plus 3 ppm BAP. Another 24 cultures were lost to a bacterial contaminant, which was provisionally identified as the plant symbiont Bacillus megaterium or a close relative. Overall, 41.5% of uncontaminated plants and 11.6% of contaminated plants produced roots in vitro, after exposure to DKW medium with 3 ppm IBA, followed by hormone-free medium, with 92.6% of the uncontaminated plants surviving the transfer to the nursery whether they were rooted or not, as opposed to 62.1% of the contaminated plants. Conclusions This methodology can be used to produce large numbers of clonal ash plants on demand from a wide cross-section of the UK’s and Ireland’s ash breeding population, and so can be used to help produce the ash plants needed to combat ash die-back disease, although contamination issues are likely to remain an issue.

Keywords

• European ash
• Ash dieback
• Chalara fraxinea
• Hymenoscyphus fraxineus
• In vitro propagation
• Rooting