| Research Abstract |
1.An attempt to determine the causes of floral bud abortion of Japanese pear associated with global warming.
1)Field survey for floral bud abortion in southern Brazil
Floral bud abortion of Japanese pear occurs throughout the southern Brazil, with higher or lower intensity. From the field survey, occurrence of floral bud abortion varies greatly among cultivars, seasons and locations, the cvs. Nijisseiki and Housui are the most affected. At the Sao Joaquim areas, one of the coldest region in Brazil, trees received only 766 chilling hours in 2005 in contrast to average year value of about 1000 chilling hours. From the results of the observations and discussions with Brazilian fellows, we assumed that the lack of chilling mainly results in abnormal pattern of budbreak and development in Japanese pear trees. We also observed similar disorders in Kyushu area, but these were now limited to forcing culture.
2)The incidence of floral bud abortion in controlled environment
Through experiments provi
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ding different amounts of chilling temperatures to Japanese pear trees before forcing the growth in the phytotron, the influence of this amount on the budbreak pattern was investigated with special regards the incidence and possible cause of floral bud abortion. The results showed that the bud abortion intensified just before flowering process, presenting normal floral primordia at the beginning of autumn.
3)Developing the phenological database for Japanese pear and its application
The flowering patterns of Japanese pear trees (cvs.Kousui) in recent years were classified into 4 types. In the first type, as typically seen in Saitama, flowering date has been advanced gradually. In the second type, flowering has been advanced only slightly. In the third type, as typically seen in Ooita, flowering date has been clearly delayed. No apparent shifts in flowering date were evident in the forth type. Harvest date was delayed in Fukuoka and Fukushima. Conversely, in Akita, Toyama, Chiba, Ibaraki and Tottori, harvest time was advanced. Yearly variation of flowering and harvest time in ‘Housui' and ‘Nijisseiki' Japanese pears was evaluated to compare with that in ‘Kousui'.
2.Dormancy and flowering control for Japanese pear in the face of global warming
The covering method using a reflective film was employed independently or together with an evaporative cooling device. The diurnal range of temperature covering above the top of the trees became smaller than that in the open field. Thus, it was expected in terms of its chilling requirement that the prolonged period of low temperatures was effective in breaking the endodormancy. Considerable drops in air and bud temperature were recorded when used with the evaporative cooling device. Moreover, high temperature treatments were performed using a growth cabinet controlled at about 32-33℃. Despite accumulation of chilling hours before high temperature treatment, intermittent heat treatments increased bud break and suppressed floral bud abortion caused by insufficient chilling temperatures. Less
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