Assessment of factors affecting adventitious shoot regeneration from in vitro cultured leaves of apricot.

Relatively high percentages of adventitious shoot regeneration have consistently been obtained from leaves of some apricot cultivars. For the cultivar 'Helena', explants from the proliferation medium were more reactive than those from the elongation medium. The best results were obtained with thidiazuron (TDZ). When 6-benzylamino-purine (BAP) was used instead of TDZ, the regeneration percentages were very low. High alpha-naphthaleneacetic acid (NAA) concentration had an important effect upon the decrease of the secretion of phenolic substances. Young expanding leaves with the adaxial side touching the culture medium, maintained for 2 or 3 weeks in darkness, produced the best results. There was a significant genotypic variability in adventitious bud formation. Several caulinar meristems arose from very small areas of the leaf but only one meristem developed to form a shoot when those buds were transferred to elongation medium. However, the fact that several caulinar meristems exist in early steps could be an advantage when genetically transforming these leaves, since a high number of cells would have the possibility of being transformed and producing adventitious transformed buds.