Dormancy release in Asian 'Hosui' pear trees with the use of vegetable and mineral oils

Pear trees planted in regions with mild winter display low bud break percentages and, consequently, low yields. Several compounds have been evaluated for dormancy release in pear trees, however, they can be toxic, impacting negatively on the environment. Therefore, the objective of this research was to evaluate the effect of different oils (vegetable and mineral) on bud break, yield and enzymatic activity in 'Hosui' pear trees. The experiment was carried out in a commercial orchard with Pyrus calleryana rootstock. The treatments were as follows: 1) untreated control; 2) 4% vegetable oil (V0) (emulsifiable); 3) 4% mineral oil (MO); 4) 4% sunflower oil (SO); 5) 4% MO + 2% VO; 6) 4% MO + 4% VO; 7) 4% SO + 4% MO; 8) 4% MO + 2% hydrogen cyanamide (HC). The following variables were evaluated: bud break percentage of lateral buds and apical buds, number of fruit tree^‑1, average fruit weight, yield, catalase activity and fruit soluble solids concentration. The highest lateral bud break percentage was found for the treatment with 4% MO + 2% VO, with results similar to the standard treatment with 4% MO + 2% HC. For the apical buds all treatments increased the sprouting percentage when compared to the untreated control. All treatments increased the number and average weight of fruit and yield, except the treatment with 4% VO. There was a reduction in the activity of the catalase enzymes in the buds of the trees treated with the different mineral or vegetable oils, indicating their mode of action is through oxidative stress, similarly to the effect of the conventional treatment with mineral oil and HC. Based on the results obtained it was verified that the application of 4% MO plus 2% VO may be a more sustainable alternative for inducing bud break in 'Hosui' pear trees.