469 On the Advancement of Bud Break and Fruit Ripening Induced by Hydrogen Cyanamide (Dormex ® ) in Sweet Cherry: A Three-Year Study A. Godini, M. Palasciano, G. Ferrara, S. Camposeo and A. Pacifico Dipartimento di Scienze delle Produzioni Vegetali Università degli Studi di Bari Via Amendola 165/A, 70126 Bari Italy Keywords: Prunus avium, ‘Burlat’, ‘Ferrovia’, chill hours, endodormancy, advanced bloom Abstract Research to ascertain the effectiveness of hydrogen cyanamide (Dormex ® ) to advance bloom and fruit ripening of two sweet cherry (Prunus avium L.) cultivars was carried out in the Apulia region (southeastern Italy) during 2002 (964 chill hours), 2003 (592 chill hours) and 2004 (834 chill hours). The effects of four concentrations of hydrogen cyanamide (0.0 as control, 2.0, 3.5 and 5.0%) and three times of application were tested on ‘Burlat’ and ‘Ferrovia’. In 2002, the best results were obtained by early treatments (57 and 50 days before natural bloom of ‘Burlat’ and ‘Ferrovia’, respectively) with all concentrations. The maximum advancement of bloom was 11 to 13 days in ‘Burlat’ and 7 to 9 days in ‘Ferrovia’. The maximum advancement of fruit ripening was 7 to 8 days in ‘Burlat’ and 6 to 8 days in ‘Ferrovia’. The unusually mild 2002/2003 winter influenced the research, greatly reducing the advancement of both bloom and ripening of the two cultivars. In 2004, early treatments (79 and 62 days before natural bloom of ‘Burlat’ and ‘Ferrovia’, respectively) achieved the best results. The greatest advancement of fruit ripening was by 7 days in ‘Burlat’ and by 8 days in ‘Ferrovia’. In general, early treatments (between 50 and 85 days before natural bloom) and low concentrations (2.0 and 3.5%), applied after a normal winter, were the best in terms of effectiveness, cost and respect of the environment. The effects of hydrogen cyanamide did not extend beyond bud break and climatic factors seemed to influence fruit growth processes from bloom onward, generally decreasing the initial gain in development. INTRODUCTION With over 50,000 t per year, Apulia is the chief Italian region for sweet cherry (Prunus avium L.) production. Almost the whole production is for the fresh market and is based on two cultivars: ‘Burlat’, which ripens early (between the 2 nd and 3 rd week of May); and ‘Ferrovia’, which ripens medium-late (between the 1 st and 2 nd week of June) (Godini, 1997). As a consequence of its optimal geographic position, Apulia is the first Italian region to harvest and market cherries. However, between the ripening of ‘Burlat’ and ‘Ferrovia’, there is a 7 to 12 day interval, and advancement in ripening of either ‘variety would mean new possibilities on both domestic and European markets. As opposed to table grape (Vitus vinifera L.), for which advanced ripening can be obtained with plastic covers applied to the tendone training system (Godini, 1991), in the case of sweet cherry, ripening could be advanced by the application of growth regulators, such as hydrogen cyanamide (Dormex ® ). This product is able to break winter bud dormancy (endodormancy) early, thus advancing bloom (Shulman et al., 1983, 1986; Erez, 1987). The mechanism by which hydrogen cyanamide exerts its effect is the inactivation of the enzyme catalase, which detoxifies hydrogen peroxide (H 2 O 2 ) by catalyzing its breakdown to water and molecular oxygen (O 2 ). The consequent accumulation of peroxides into the cells leads to metabolic reactions which stimulate the plant to break the dormancy (Shulman et al., 1986). Studies on different stone fruit species, including sweet cherry, showed that the Proc. 5 th IS on Cherry Eds.: A. Eris et al. Acta Hort. 795, ISHS 2008