Abstract
A japonica rice (cv.Koshihikari) was used to test the effects on blooming and ripening of UV-B radiation treatment combined with high temperature treatments (day/night, 35 / 30°C). Strong UV-B radiation (60.4 kJ/m2 · day) slightly increased sterility. High temperatures and weak UV-B radiation (18.1 kJ/m2 · day) applied together from two weeks before heading and from the heading day increased sterility and those applied from two weeks after heading decreased sterility. High temperature combined with strong UV-B radiation applied from two weeks before heading increased sterility and decreased the size of unhulled grain and anther length. The same treatment given from the heading stage greatly increased sterility and decreased anther length and pollen production, and that given two weeks after heading decreased unhulled grain weight. It also decreaed photosynthetic rate in Flag leaves. A high temperature applied together with strong UV-B radiation had a synergistic effect causing poor growth; it increased the harmful effects of a high temperature and sttong UV-B given separately, on the sterility and pollen formation.
