6-BA and NAA effect on ‘Galaxy’ fruit growth, abscission and quality: a comparison between the Po Valley and the South Tyrol producing areas

The present study concerned the fruit thinning efficacy of the cytokinin 6-benzyladenine (6-BA) at 150 ppm alone or in combination with the naphthalene acetic acid (NAA) at 15 ppm, on ‘Galaxy’ trees grown in two orchards, one in South Tyrol and the other in Emilia-Romagna area. Applications were carried out at different fruit sizes (5–7, 10–12, 14–16mm of the king fruit diameter, KF Ø). In warm climatic conditions as in Emilia-Romagna, the best thinning efficacy was observed with the application of 6-BA alone when KF Ø reached 10–12 mm, while in South Tyrol, where climatic conditions are cooler than Emilia-Romagna, 6-BA alone showed its best thinning efficacy when KF Ø reached 14–16 mm. However, in this area, the best results were obtained with the combination 6-BA + NAA applied at 5–7mm KF Ø. Moreover, all the chemical applications positively affected fruit quality traits at harvest and, in particular, soluble solid content and flesh firmness were higher in treated fruits as compared to control ones. In South Tyrol, the chemical thinners enhanced skin red colour.