Vibrational response of the male ‘peter’ pistachio branch organs to facilitate artificial pollination

Abstract

Artificial pollination may be a promising practice to both improve fruit production and establish new pistachio-producing areas, thus mitigating the losses caused by phenological gaps or by adverse meteorological events. Artificial pollination requires large quantities of pollen, but manual collection is not economically viable. Mechanised pollen harvesting could be carried out in two ways: by detaching either the mature pollen from the flower and capturing it in the air, or the mature male flowers and releasing the pollen in the laboratory. In this work, the dynamic behaviour of branches of the male 'Peter' variety was analysed under controlled laboratory conditions. A wide range of vibration frequency values was used for branch excitation, and the responses of the stem and inflorescences were analysed. The stem and inflorescences had clearly differentiated dynamic responses according to the vibration frequency. The stem attained maximum acceleration transmissibility values at specified frequency values (8, 13.5, 20.5-22 Hz). At these values, the vibration applied amplified the movement of the branches and the release of pollen into the atmosphere. At the highest frequency values (45 Hz), the stem damped the vibration, but the inflorescences amplified the response. In the 54-59 Hz range, the inflorescences amplified the acceleration received by an average value of 5-41 fold. In this range, detachment of the inflorescences is facilitated without exciting the stems. Commercial trunk shakers must be adapted if they are used to collect pollen from pistachio trees owing to the higher transmission values of trees without leaves.