Most of the European and Asian pear cultivars, when cultivated under mild winter such as in Southern of Brazil, have adaptation problems. The temperature oscillations during the winter and the little chilling hours accumulation have been considered by some researchers as causes of flower bud abortion. The purpose of this study was to determine the levels of carbohydrates in tissues of flower buds of the two pear cultivars: Kieffer (P. communis x P. pyrifolia) and Housui (P. pyrifolia). Flower bud and its surrounding base tissues (bud cushion) were monthly collected since February until September 2002, from pear trees in a orchard of Embrapa Temperate Climate Research Center (32°51' S and 52°21'W), located at 230 m of altitude. The tissues of the flower buds and bud cushion were separately analysed for soluble sugars concentration (by GLC) and starch percentage (by spectrophotometry), in the Laboratory of Plant Physiology of Embrapa. It was observed that the bud cushion tissue is an important site of starch accumulation on both cultivars. There were marked increases in soluble sugars in the flower bud tissues of both cultivars, previously to budbreak. However the total soluble sugars accumulation in the buds of cv. Housui, in September (38,33 mg g-1 DW dry weight), were lower than those of cv. Kieffer (50,39 mg g-1 DW), which has better adaptation. Sorbitol followed by sucrose was the more abundant water soluble sugar in both tissues of the two cultivars.
Pyrus sp.; soluble sugars; sorbitol; sucrose; starch; flower bud abortion
