Abstract

The present study was conducted in San Clemente, Chile (35° 33' S lat; 71° 24' W long), during the 1996-1997 and 1997-1998 growing seasons, and was aimed to determine the approximate induction and flower differentiation dates on apples (Malus domestica Borkh.) cvs. Royal Gala, Fuji, Red Chief and Braeburn. Induction date was determined by applying gibberellin GA4+7 (l00 mg kg-1) and weekly manual thinning, from full bloom up to 70 days after full bloom (DDPF). Flower differentiation was evaluated by collection and tissue dissection of floral buds, between December 1996 and June 1997. The period of maximum sensitivity of flower induction could only be determined by gibberellin application, which and was found between 7 and 21 DDPF for R. Gala, R. Chief and Braeburn. Trials related with flower induction had high variation coefficients (22 to 57%), probably due to the rootstock (seedling), low G 4+7 concentration or inefficient thinning, and mainly due to high tree vigor, as shown by shoot length, 50 cm in on average, which is almost twice of that recommended in other foreign literature. Nevertheless, data suggest that this event occurred about 14 and to 21 DDPF for GA4+7 experiments, and around 35 days DDPF for thinning experiments. Flower differentiation was determined on January 6, 1997 (100 DDPF) in cv. Fuji, R. Chief and Braeburn, and January 20 (114 DDPF) in cv. R. Gala. © 2006 Instituto de Investigaciones Agropecuarias, INIA.