FLOWERING AND FRUITSET

Avocado flowers are dichogamous which means that the female stage and the male stage are separated in time. A very unusual phenomenon is the fact that the flower closes after the female phase, re-opens for the male phase and closes again after the male phase. Opening of the flower in the female phase involves the unfolding of the perianth leaves to expose the pistil with its receptive stigma for a few hours and then closing again. The next day, in the morning or in the afternoon, depending on the cultivar, the flower will reopen to expose the dehiscing anthers which will then shed the pollen grains (Davenport, 1986). There is a major difference between A and B-type cultivars regarding the time of opening and closing of flowers of the two sexual phases. Opening of the flowers is mainly controlled by environmental conditions, of which temperatures seem to be the most important. In unfavourable weather conditions, the rhythm of the flowers can, however, be totally disturbed on certain days so that flowers will not open at all, thus excluding the possibility of pollination and fruit set (Robbertse et a/., 1996). Pollination is the transfer of pollen from the anthers to the receptive stigma. Avocado pollen is sticky and heavy and therefore suitable for insect-pollination. Different insects are foun