FLORAL BUD INITIATION AND DEVELOPMENT OF THREE PEAR TREE (PYRUS SP.) CULTIVARS IN TWO SUBTROPICAL REGIONS DURING THE SUMMER PERIOD

Abstract

The flower formation in fruit trees is in the spring but actually begins in the previous summer. Flowers are induced in the apex of the buds, which were vegetative previously. After flower induction, which is still an unknown process, successive steps of physiological processes occur and morphological differentiation, when the apex becomes organized into a primordia of flower (or inflorescence). The first morphological change that occurs in the meristem is a 'broadening' of the apex, which also becomes convex, followed by its lengthening into a cylindrical shape and the formation of sepal primordia in the terminal flower (king flower). After this transformation, organ primordia become differentiated laterally. The time of floral bud formation in the fruit trees is of great importance, because it will determine the development level that these buds will reach before beginning the dormancy period, having a decisive effect on the quality of the produced inflorescence. The objective of this work was to investigate the time of floral bud initiation and development in three pear tree cultivars ('Packham's Triumph', 'Abate Fetel' and 'Housui') in two subtropical regions of Rio Grande do Sul state (Pelotas and Vacaria) during the growth period in 2007. To evaluate the floral bud initiation, terminal and axillary buds of long shoots and apical buds of spurs were collected from January 9 th , in a 15-day interval, until march 14 th , fixed in a solution of formalin, acetic acid and alcohol (FAA) and dissected under a stereoscopic microscopy in the Laboratory of Imunology and Electronic Microscopy at Embrapa Clima Temperado, Pelotas-RS. The time of floral bud initiation did not practically differ between the two regions to the three cultivars observed. However, the time of floral bud initiation differed between cultivars and, also, the three cultivars presented a differentiated behavior in the flower bud development. In the beginning of the observations, the spur buds of 'Housui' had already initiated and presented in more advanced stages of floral development than the other two cultivars. The floral initiation in the 'Packham's' spur buds and in the 'Housui' terminal buds occurred in late January. The spur buds of 'Abate Fetel', terminal buds of 'Packham's' and axillary buds of 'Housui' were initiated in early February. In the middle of March, the spurs of 'Housui' and 'Packham's' and the terminal buds of 'Housui' reached the carpel primordia stage.