Effect of Temperature during the Ripening Period on the Induction of Secondary Dormancy in Rice Seeds (Oryza sativa L.).

Abstract

Our previous work on the induction of secondary dormancy at a lower germination temperature showed that evaluation of germinability at a lower temperature was much affected by the secondary dormancy. Here, the effect of temperatures during the ripening stage on the degree of induction of secondary dormancy was investigated for rice seed of two Indica cultivars, Kasalath and Dhenga. In both cultivars, the germination percentage of the seeds ripened under the high temperature condition of 32°C/27°C was lower than that of the seeds under the control condition of 25°C /19°C after low temperature treatment at 15°C for 14 days. In the continued germination test conducted at 25°C for 7 days, the germination percentage was not increased for the seed from both conditions with a lower percentage for the seeds from the high ripening temperature and a higher percentage for the seeds from the control condition. The non-germinated seeds were considered to be induced into secondary dormancy. Thus, the seeds which ripened at a high temperature showed a comparatively deep secondary dormancy. The effect of the temperature at the ripening stage on the wakening of secondary dormancy was also investigated by storing the seed for eight months at 30°C. The germinability of the seeds from the high temperature condition was lower than that of the seeds from the control condition. The difference was gradually decreased in the course of storage. The temperature during the ripening period of seeds affected the wakening of secondary dormancy.