Response of three new apple cultivars to chemical thinning in Italy (Trentino)

In Trentino, as in other apple-growing regions of Europe, there has been a rapid introduction of new club apple cultivars. The knowledge of the agronomic practice of each cultivar is crucial for establishing proper fruit load management. This study investigated the apple cultivars ‘Minneiska’, ‘Kizuri’, and ‘Gradisca’. We tested some of the most commonly used plant growth regulators (PGR) for thinning, with a particular focus on 6-benzyladenine (6-BA). ‘Minneiska’ was found to be easy to thin in both years of evaluations and showed a positive response to cytokinin application. When not thinned, it exhibited alternate bearing. ‘Kizuri’ responded well to thinning: a strategy that combined ATS during flowering and 6-BA on the fruitlets showed good results. However, the addition of metamitron at high doses resulted in excessive thinning. Overall, the return bloom was satisfactory. ‘Gradisca’, on the other hand, proved to be the most difficult cultivar to thin: the fruit set was generally high, and early experiences indicated the necessity for a strong thinning strategy. Effective results were achieved through early applications on the flowers followed by the addition of a partner like NAA to the 6-BA. More intensive thinning strategies resulted in improved return bloom.