Residual effects of High Temperature Pre-Treatments on the Germination of Celery Seeds (Apium graveolens)

Celery seeds (Apium graveolens L.) were allowed to imbibe in the dark for different periods at 28. 32. 37 or 41°(the high temperature pre-treatmem or HTP) prior to transfer to 15, 17, 19.5 or 22°C in white light (the low temperature treatment or LTT). The effect of HTP's at 28. 32 and 37°C was to lower the upper temperature limit for germination and this effect increased with increase in the temperature and duration of the HTP. Increasing exposure to an HTP of 41 °C, however, did not appear to lower the upper temperature limit for germination but reduced the viability of the seeds. This trend of increased inhibition of germination caused by increasingly higher temperatures was reversed when the transfer was to a 22°C LTT after a 4 day HTP at 37°C. When the temperature of (he HTP was relatively low and transfer was to a low LTT. or if the HTP was of a brief duration, the rate of germination was increased as compared to seeds not given an HTP. However, when the temperature and duration of the HTP were increased, the rate of germination became slower than that of seeds not given an HTP, i.e. the time taken for the seeds to recover from the HTP-induced dormancy increased with the temperature and duration of the HTP. The decrease in the germination rate was caused by a delay in the start and not a slowing of the rate of embryo elongation within the seed.