SHOOT INITIATION IN THE LEAFLET AXILS OF COMPOUND LEAVES FROM MICROPROPAGATED SHOOTS OF JUVENILE AND MATURE COMMON ASH (FRAXINUS-EXCELSIOR L)

Micropropagation of a mature ash tree has been achieved for the first time. The main obstacle encountered was contamination of the initial e xplants with microorganisms. However, once apparently sterile shoots h ad been obtained, shoot proliferation was achieved most effectively by culturing nodes on Driver and Kuniyuki walnut medium containing 22.2 mu M benzyladenine. After several subcultures, a species of Bacillus a ppeared with the mature culture line, but it did not affect shoot or r oot development adversely. With successive subculturing, shoots of the mature ash clone became progressively easier to root. Pinnately compo und leaf explants from micropropagated shoots of two seedlings and the mature tree, on to Murashige and Skoog-based culture media supplement ed with 4.4 mu M N-phenyl-N'-1 ,2,3-thiadiazol-5-ylurea, produced shoo t buds. Most buds developed from the rachis at the points of attachmen t of the leaflets. When transferred to Driver and Kuniyuki walnut medi um, buds from one of the seedling lines and from the mature tree, elon gated into shoots, and were subsequently transferred to media for micr opropagation and rooting. Shoot initiation is discussed in relation to possible occurrence of vestigial meristems in the axils of leaflets a nd the partial shoot theory of leaf structure.