Germination and Radicle Growth Characteristics of Presowing-treated Carrot Seeds Affected by Low Temperatures.

Abstract

In carrot, germination of imbibed and primed seeds, and seedling radicle growth of imbibed, primed, pregerminated, and primed + pregerminated seeds were compared with those of untreated seeds at optimal and low temperatures. Percentage germination of untreated seeds exposed to 2 degree and 4% C decreased remarkably compared to those kept at 25 degree C. However, the percentage germination for primed seeds decreased slightly or showed no decrease even at 2 degree C, whereas, a moderate decrease was observed for imbibed seeds. These results indicate that priming or imbibing seeds lowered threshold temperatures for germination. Mean germination time increased at lower temperatures with more days for untreated seeds and a very few days for primed seeds. The mean germination time was shorter for imbibed seeds than it was for untreated seeds, but the effects of both treatments were not relatively different when compared to that at 25 degree C. Integrated degree-day for germination to occur increased at a similar rate for untreated and imbibed seeds as temperatures were lowered, but in primed seeds it did not increase even at 2 degree C. This finding suggests that priming treatment accelerated germination at low temperatures by causing some physiological changes which were not directly related to the advancement of the germination stage. Coefficients of variation in germination time for primed and imbibed seeds were considerably greater than that for untreated seeds. There was no consistent relationship between coefficients of variation in germination time and temperatures. Seedling radicles of primed seeds elongated very rapidly; those of imbibed and pregerminated seeds slightly more rapid than that of untreated seeds. Effect of these presowing seed treatments on the elongation of radicles was not enhanced at 10 degree C compared with that at 25 degree C.