Electrostatic pollination in apple (Malus domestica Borkh.) ‘Cripp's Pink’

Reproductive efficiency is a key determinant of yield in apple production (Malus domestica Borkh.), particularly in self-incompatible cultivars whose production depends on cross-pollination mediated by insects. In Uruguay, high climatic variability during flowering may limit pollinator activity, resulting in pollination deficits that affect fruit set and yield stability between seasons. In this context, artificial pollination represents a potential strategy to complement natural pollination and improve reproductive efficiency in apple orchards.

The aim of this thesis was to evaluate the effect of electrostatic application of compatible pollen, either alone or in combination with insect-mediated pollination by honeybees (Apis mellifera), on fruit set, fruit number per tree, and fruit quality parameters in the ‘Cripps Pink’ cultivar under commercial production conditions in southern Uruguay. The study was conducted over three consecutive production cycles, from spring 2020 to harvest 2023, comparing treatments with pollinator exclusion, insect-mediated pollination, electrostatic pollination, and a combination of both strategies.

Natural pollination showed greater efficiency in fruit set than electrostatic pollination when used as the sole pollen source, resulting in a 24% higher percentage of fruit-setting flower clusters. Electrostatic pollen application, even when used as the sole pollen source, achieved 7% fruit set, with values ranging from 44 to 61 fruits per tree depending on the production year. For fruit number per tree, significant differences among treatments were observed in different production year, with electrostatic pollination resulting in a higher number of fruits than the pollinator-exclusion control in two of the three years, corresponding to yield increases of 17 and 23 t ha⁻¹. In addition, during the 2020, a significant additive effect of electrostatic pollination was observed when combined with natural pollination. Overall, natural pollination and the combined strategy showed the highest values for fruit set and fruit number per tree.

The number of seeds per fruit and fruit size showed high variability and did not exhibit a consistent pattern associated with the pollination treatments. Overall, the results indicate that electrostatic pollination can be used as a complementary tool to provide compatible pollen and improve fruit set and fruit load under certain conditions, but its use as a stand-alone strategy cannot replace natural pollination mediated by honeybees.