PHENOL INDUCED BROWNING AND ESTABLISHMENT OF SHOOT-TIP EXPLANTS OF FUJI APPLE AND JINHUA PEAR CULTURED IN-VITRO

Several factors influencing phenol induced browning and establishment of apple (Malus pumila Mill. cv. Fuji) and pear (Pyrus bretschneideri Rehd., cv. Jinhua) were investigated by using shoot-tip explants cultu red in vitro. Explants of 'Fuji' apple and 'Jinhua' pear collected fro m November to February produced low browning percentages. Browning per centages increased rapidly as the stock plants entered the growing sea son, reached a maximum during April and August and then decreased. Dar k treatment of the stock plants reduced browning. Lowest incidence of browning and the highest surviving percentages of both 'Fuji' apple an d 'Jinhua' pear were obtained after four weeks of dark treatment. Howe ver, bud-break percentage, fresh weight and the number of new leaves o f the surviving explants decreased with increase in the length of dark treatment. When the dark treatment was used during the first phase of culture initiation, 5-degrees-C was better than 24-degrees-C for redu cing browning and improving establishment of the explants. At 5-degree s-C, 6 d of dark treatment for 'Fuji' apple and 8 d for 'Jinhua' pear produced the least browning and the highest surviving percentages. How ever, bud break percentages, fresh weights and numbers of new leaves d ecreased as the length of the dark treatment increased. Addition of 2. 5 g l-1 activated charcoal to the initiation medium favoured establish ment of 'Jinhua' pear explants and 1001150 mg l-1 ascorbic/citric acid were effective with 'Fuji' apple.