Developmental events in differentiating floral buds of four olive (Olea europaea L.) cultivars during late winter to early spring

The olive tree (Olea europaea L.) is a very important evergreen fruit tree because of the high interest of olive oil and table olives in the human diet. Differentiation of olive floral buds during winter is strictly related to flowering during spring and finally to fruit production during autumn–winter. In order to determine which are the developmental events in differentiating olive floral buds we studied in four olive cultivars “Amfissis”, “Kalamon”, “Manzanillo” and “Chalkidikis” the anatomical progress of the ontogeny using median longitudinal sections of floral buds (cutting odd nodes), in weekly intervals from early February (initiation of differentiation) to mid-April (one week after floral bud burst) keeping the cultivars under the same environmental conditions. At the same time, we determined the changes in their water extractable proteins, as an index of the meristematic activity. At the beginning of differentiation, floral buds consisted of the apical and one pair of developed (odd) axillary meristems which were covered with the corresponding bracts. Floral buds showed a slow gradual enlargement in all cultivars. The sequence of the developmental events (initiation of intense mitotic activity in the apical and the first axillary meristems, initiation of mitotic activity in the second axillary meristem, development of the third pair of bracts (except from cv. Chalkidikis), appearance of mitotic activity in the third axillary meristem, swelling of apical and axillary meristems and appearance of primordial whorls) are presented comparatively. All cultivars showed similar ontogenetic trends but there were temporal differences in the initiation, the progress and the completion of the process. Cv. Amfissis initiated differentiation one week later compared to the other cultivars, also delaying the development of the second and the third axillary meristems. On the other hand, cvs. Kalamon and Chalkidikis delayed one week to complete the process when compared to cvs. Amfissis and Manzanillo.