The study was conducted for 3 consecutive years to evaluate the effect of continuous high temperature conditions on the performance of 6-year-old Japanese pear (Pyres pyrifolia Nakai cv. Kosui). Under high temperature condition, the physiological characteristics of Japanese pear changed, namely, in the first year, pear trees that were transferred to a greenhouse in July and September were more vigorous than those transferred in November. During the autumn and spring, trees transferred in July did not accumulate sufficient chilling temperature, affecting the shoot growths in the later years; those transferred to the greenhouse in September had the shortest shoots compared to trees transferred in October and November. Trees which were transferred in November had earlier budbreak, better flower buds, flowered more uniformly, and set more fruit than did trees which were transferred in July and October. Furthermore, pollen grains from Treatment 3 germinated better than did those from trees in Treatment 1 and 2. Similar results were obtained in 2nd and 3rd seasons.
Our analyses revealed that sugars increased in autumn just before dormancy while starch decreased. When the growth resumed in spring, starch increased and sugar decreased. Trees transferred to the greenhouse later which received more chilling had a higher starch and sugar contents.