Shoot organogenesis from apricot meristematic bulks

Regeneration from apricot mature tissues, previously attempted as a tool to transform susceptible cultivars with PPV resistance genes, turned out to be a very challenging goal. An alternative approach, called 'meristematic bulk' that was reported to be successfully applied to the genetic transformation of peach and other fruit species, was attempted. In this approach shoot organogenesis was achieved by obtaining, through cytokinin treatments, a highly morphogenic stem tissue from the proximal part of micropropagated shoots. Three apricot cultivars ('Boreale', 'San Castrese', and 'Vitillo'), known as recalcitrant to tissue culture, are being tested for regeneration using this method. In addition to cytokinins, other phytoregulators, as well as ethylene inhibitors, seem to play an important role first in the production of meristematic bulks, then in the adventitious shoot formation subsequent to bulk cutting. In view of the possible recovery of transgenic shoots from future transformation experiments, methods are pursued promoting a short proliferation callus phase and a delayed shoot differentiation, instead of the prompt development of preformed buds. Very promising results have been obtained from all the cultured genotypes.