The effects of global warming have been observed in several crops as changes in temperature-dependent processes, such as dormancy in perennial fruit trees. We exposed potted Japanese pear 'Housui' plants to 600 chilling hours (CH) below 7.2°C, which is below the theoretical requirement. Such low chilling accumulation was initiated at different times (three treatments) and carried out during four consecutive seasons in order to observe the influence of these factors on the incidence and severity of floral primordia necrosis, water dynamics, phenological, and morphological changes during dormancy in lateral mixed buds, which is comprised of vegetative and reproductive primordia, obtained from the current season's shoots. The submitted amount of chilling temperatures brought about the release of dormancy stage, regardless of seasonal variations in the duration to accumulate 600 CH, but caused a remarkable increase of floral primordia necrosis and a great increase in the number of floral primordia as a consequence of the development of new inflorescences; however, these morphological changes did not increased number of opened flowers because of the progression of floral primordia necrosis. Consecutive seasons of mild winter conditions anticipated the incidence of floral primordia necrosis. The results obtained from magnetic resonance imaging in the buds of plants subjected to low chilling accumulation showed low water mobility and water content especially in scales compared to plants grown under natural conditions. In contrast, increased water mobility and relative content were observed in specific portions of the bud base in treated buds, which was more accentuated in the mixed buds of plants grown for several seasons under mild winter conditions. Moreover, abnormal functional water movement inside dormant mixed buds might result in the necrosis of floral primordia, giving way to the development of new inflorescences.

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<p>O objetivo deste trabalho foi determinar o conteúdo de água e de carboidratos em ramos de pessegueiro durante o inverno, na região de Pelotas, no Rio Grande do Sul. Foram realizadas coletas quinzenais de ramos do ano de pessegueiros ‘Jubileu’ e ‘Eldorado’, entre os meses de junho e agosto/2010. Os ramos foram divididos em três secções: basal, mediana e apical, sendo que para determinação do conteúdo de água, estes foram divididos em dois tecidos: casca e lenho. Para o teor de carboidratos, foram analisados nas secções dos ramos o conteúdo de açúcares solúveis totais, sacarose e amido pelo método antrona. O conteúdo de água no tecido da casca não mostrou alterações nas duas cultivares ao longo do período analisado. Verificou-se que a dinâmica do conteúdo de água e de carboidratos apresentaram um grande aumento principalmente na secção apical do ramo próximo à brotação. Conclui-se que a dinâmica do conteúdo de água e carboidratos podem ser considerados marcadores fisiológicos para a retomada do crescimento para frutíferas de clima temperado.</p>

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