Xylem vessel differentiation and microsporogenesis evolution in 'Canino' cultivar growing in three different climatic areas: Italy, Morocco and Turkey

The aim of this research was to study the relationship between the end of dormancy, xylem vessel differentiation and microsporogenesis in flower buds of cultivar 'Canino' growing in three different environmental conditions (Italy, Morocco and Turkey). In each country flower buds were collected from December to February from one year old mixed twigs and then fixed in FAA for histological observations by optical microscope. Climatic parameters (rainfall, relative humidity, minimum and maximum daily temperatures), cumulated Chill Units and blooming time were also recorded. The histological observations showed that microsporogenesis and the most significant 'stage 3' of xylem vessel differentiation (secondary helicoidal thickening from the base up to the 3/4 of the flower bud axis) seemed to be related to a threshold of cumulated Chill Units. In Italian and Moroccan environmental conditions did tetrads and 'stage 3' appear at the same time, after about 1000 Chill Units were cumulated. In Italy these signals arise a little earlier compared to the classical biological method commonly used to establish the end of endo-dormancy.