Seasonal periodicity of the loss of dormancy of imbibed seeds in Brassica vegetables

Abstract

The present study deals with the mode of loss of dormancy of imbibed seeds in Brassica japonica and B. cernua. Mature seeds were sown in petri dishes immediately after harvest and were placed either at room temperature or at a constant temperature of 25°C. After the first flush of germination of non-dormant seeds, most seeds continued to be in a non-germinating state, suggesting that they were dormant. The germination of such dormant seeds occurred sporadically during several years. Under constant 25°C, the germination behaviour of the imbibed seeds was “quasi-simultaneous” in B. japonica and “continuous” in B. cernua. Both species showed a unimodal distribution of germination in time. Under fluctuating room temperature, the distribution of seed germination in each species was characterized by 3 peaks which occurred in summer. In B. japonica the 3 peaks were the same in height, but in B. cernua the middle peak was much higher than the other 2. Such seasonal periodicity of germination was caused by environmental factors of which temperature was the most important.