Tree growth characteristics and flower bud differentiation of sweet cherry (Prunus avium L.) under different climate conditions in China

The phenological stages, flower characteristics, shoot growth and flower bud differentiation of sweet cherries, cv. Hongdeng and Van, were investigated in different climatic zones in China, subtropical monsoon climatic zone (Shanghai, 31 degrees 14'N, 121 degrees 29'E) and temperate climatic zone (Qingdao, 37 degrees 09'N, 121 degrees 20'E). Sweet cherry trees grown in subtropical monsoon climatic zone had earlier phenological stage and longer blooming duration than those grown in temperate climatic zone. Fruit growth periods of Hongdeng and Van in Qingdao were 38 days and 51 days, respectively, but only 29 days and 45 days in Shanghai. Both cultivars showed more abnormal flowers under subtropical monsoon climate. The percentage of fruit set under open pollination in Hongdeng and Van were 31% and 24% in Qingdao, respectively, but only 0.4% and 3.2% in Shanghai. The trees grew more vigorous in Shanghai; flower bud differentiation was delayed by high temperature and superabundant rainfall in subtropical monsoon climate zone and more easily affected by the overlap of current shoot growth.