Pollen collection
For each cultivar, five trees were randomly chosen at
the blossoming stage, 20 inflorescences per tree were
selected at random throughout the canopy in the
middle position of fruiting shoots and the number of
flowers counted. It is well-known that each small
olive flower bears two anthers whose time of
dehiscence is unpredictable; therefore, instead of
single anthers, six samples of five flowers each per
cultivar (i.e. 60 anthers) were removed from the
inflorescences and placed in six vials (10 anthers6
vial) closed with a gauze. The flowering and
dehiscence of anthers were obtained at room
temperature in the vials within 2–3 days.
Successively, 4 ml of a 5% aqueous solution of
polyoxyethylene-sorbitan monolaurate (Tween
20)
were added to each vial and the solutions were
treated with an ultrasonic probe vibrating at 20 kHz
for 25 s to facilitate the removal of pollen grains
from the anthers.