PERIOD OF HARVEST, SPROUTING ABILITY OF CUTTINGS, AND IN-VITRO PLANT-REGENERATION IN FRAXINUS-EXCELSIOR

Propagation by stem cuttings and in vitro culture of apical bud explan ts were studied on Fraxinus excelsior L. Stem cuttings from 4- to 7-ye ar-old trees growing under natural conditions sprouted only when cutti ngs were taken from dormant material. Only 6% of those that had sprout ed developed roots by the 7th month of culture. Similarly, only apical bud explants harvested during the dormant period sprouted in vitro. U p to 87% of these sprouts developed two to four branching adventitious roots after 5 months of culture. During the initial phase of in vitro culture, the Quoirin and Lepoivre medium and the woody plant medium f avoured sprout lengthening. During the phase of multiplication, up to three sprouts per explant developed with the woody plant medium in the presence of a combination of high 6-benzylaminopurine (3.0-4.0 mg.L(- 1)) and low indole-3-butyric acid (0.01-0.03 mg.L(-1)) concentrations. Rooting was obtained in a medium without any growth regulators. Micro scopic analysis showed a direct connection between the vascular elemen ts of adventitious roots and stem of plantlet. Chromosome number in ro ot apices of ash plantlets and ash trees grown under natural condition s was 2n=46.