A novel strategy for the induction and maintenance of shoot regeneration from callus derived from established shoots of apple [Malus x Domestica Borkh.] cv. Golden Delicious

A novel strategy for the production and maintenance of morphogenic callus for 1 year from mature leaf explants of apple has been developed using micropropagated primary leaves of cv. Golden Delicious. The technique required second generation adventitious buds produced from cultured primary leaves also produced from established shoot cultures. The age at which buds were capable of producing morphogenic callus was critical and found to be when leaflets were 2-3 mm in length. Medium composition affected the maintenance but not the induction of shoot regeneration from callus and the best combination was found to be high calcium, low ammonium and low hormone levels. Adventitious shoots were rooted in vitro and established glasshouse-grown plants showed no phenotypic differences from the plants derived from shoot proliferation. The great advantage of this technique for an increased efficiency of recovery of transgenic plants from transformed cells is discussed and the acquisition and maintenance of cell competence with respect to the formation of shoots in culture is explained.