EFFECTS OF SHORT-DAY PHOTOPERIOD ON THE GROWTH OF ASPARAGUS IN AUTUMN

In Japan, asparagus ferns undergo yellowing in autumn, and the germination of the buds is suppressed even when they are exposed to optimum temperatures. This phenomenon is called “dormancy”, and low temperatures are necessary for breaking dormancy. To harvest asparagus during winter, forcing culture is performed in part by using dug rootstocks. This method is called “Fusekomi forcing culture”. While the major factor affecting the induction of dormancy is the cumulative exposure to chilling temperatures, the photoperiod is also considered to be a possible factor affecting the induction of dormancy. In this study, we investigated the effect of short-day photoperiod on asparagus growth in autumn by using 1-year-old ‘Welcome’ plants. The plants were sown in early February and grown in non-woven fabric pots with a diameter of 25 cm. From late August, these pots were subjected to 8-h short-day photoperiod (SD) or natural photoperiod (ND; average time, 12 h 06 min). After the treatment, the pots were placed in a greenhouse, and the soil temperature was adjusted to 16°C. There was no difference between the yellowing of asparagus ferns in the SD- and ND-treated plants. The number of stems in the SD-treated plants was slightly greater than that in the ND-treated plants; the plant height in the former group was lower than that in the latter group. The brix value of the root increased with time; the value for the ND-treated plants was greater than that for the SD-treated plants. The root weight showed a similar trend. However, if the temperature of the surroundings is suitable for breaking bud, SD and ND treatments do not have any difference. On the basis of these results, we believe that the dormancy of 1-year-old asparagus in autumn was not influenced by short-day conditions; rather, it was affected only by the reduction in photosynthesis.