Assessment of regeneration and transformation in sweet cherry cultivars

The sheer size of the tree is still one of the most relevant cherry-growing related problems. Genetic transformation with phytochrome genes could contribute to the reduction of tree size in cherry. The responses to morphogenesis and genetic transformation were compared in two sweet cherry commercial cultivars and the characterised somaclone HS. Axenic shoot cultures of ‘Hedelfinger’, ‘Lapins’ and somaclone HS were grown on BA (6-benzylaminopurine) containing medium. The apical portion of each shoot was cultured in the presence of BA and NAA (naphthalene acetic acid) in the dark. After two weeks the callus formed at the base of each shoot, a 3-4 mm upper stem portion deprived of axillary shoots/buds and intact leaves were subcultured on regeneration medium, in the light. A. tumefaciens (C58C1 pGV3850), carrying the p35SGUSIntron binary vector was used to infect shoots deprived of unfolded leaves and lateral buds by either full immersion or basal dipping in the bacterium suspension. After 21 days under light, all tested explants, except ‘Lapins’ stems, showed regeneration ability. All reached their maximum regenerative expression within 56 days and ‘Lapins’ basal callus scored the highest regeneration percentage (50.1%). Basal dipping was chosen as the optimal system to infect the two cultivars and the somaclone which showed a different attitude to produce morphogenic callus. The morphogenic masses kept growing on 50 mg L-1 kanamicine for 40 weeks and the first shoots started to elongate when the BA was reduced by one-fourth. GUS activity was found in the shoot basal cuts and surrounding tissues and this evidence let us deduce that hypothetically transformed cells had chances to take part in either direct or indirect morphogenesis.