A NOVEL STRATEGY FOR THE INDUCTION AND MAINTENANCE OF SHOOT REGENERATION FROM CALLUS DERIVED FROM ESTABLISHED SHOOTS OF APPLE [MALUSXDOMESTICA BORKH.] CV GOLDEN DELICIOUS

A novel strategy for the production and maintenance of morphogenic cal lus for 1 year from mature leaf explants of apple has been developed u sing micropropagated primary leaves of cv. Golden Delicious. The techn ique required second generation adventitious buds produced from cultur ed primary leaves also produced from established shoot cultures. The a ge at which buds were capable of producing morphogenic callus was crit ical and found to be when leaflets were 2-3 mm in length. Medium compo sition affected the maintenance but not the induction of shoot regener ation from callus and the best combination was found to be high calciu m, low ammonium and low hormone levels. Adventitious shoots were roote d in vitro and established glasshouse-grown plants showed no phenotypi c differences from the plants derived from shoot proliferation. The gr eat advantage of this technique for an increased efficiency of recover y of transgenic plants from transformed cells is discussed and the acq uisition and maintenance of cell competence with respect to the format ion of shoots in culture is explained.