The commercial exploration of the pear culture in Brazil has little expression, due to the low productivity of the plants, being the internal consumption supplied by imports. The lack of adaptation and flower bud abortion (bud jump or floral bud drop), are the main problems for the development of the crop. The aim of this work was to evaluate the occurrence time and the intensity of the flower bud necrosis and of the inflorescence duplication in pear trees cv. 'Housui' (Pyrus pyrifolia (Burm.) Nak.) during the dormancy period. The experiment was conducted in 2007, using 14-year-old pear trees, and it was carried out in a completely randomized design, with three replicates. In each replicate, five terminal and axillary buds of shoots and five spur buds were collected on four dates from May 24th, in an approximate 30- day interval, until August 24th. These buds were 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 of the Embrapa Clima Temperado, Pelotas - RS. In each sampling the parameters evaluated were the percentage of healthy buds, buds with moderate and severe necrosis and beyond, the percentage of buds with duplicated inflorescences. In the beginning of winter, practically all the buds analysed already presented inflorescence duplication. However, during this phase, the flower bud necrosis symptoms were not present. The 'Housui' cv. was seriously affected by the necrosis only in the final period of dormancy, with high index of buds affected. The symptoms of necrosis began rising from a negligible level in the beginning of the winter to a sharp peak near to the onset of flowering. The inflorescence duplication causes the formation of a very large number of less vigorous floral primordial that increase the competition for the nutrients and assimilates and can provoke the exhaustion of the nutritional reserves, leading the necrosis of the flower primordial tissues.
