アサツキの生長力の季節的変動と休眠

Abstract

Asatsuki is a bulbous Allium species and is cultivated for its edible leaves, which are harvested in late winter and early spring. Asatsuki grows from autumn to spring and dies down after producing dormant bulbs in early summer.Innate dormancy of roots of asatsuki bulbs ended in early July, and that of leaves in early August. However, hot summer temperatures of 25°Cor higher inhibited rooting and sprouting of the bulbs in the field, so that the bulbs rooted from early August onwards and sprouted from late August onwards.Optimum temperatures for root growth after rooting were 21 to 25°C, and those for leaf growth after sprouting were 17 to 25°C.After termination of innate dormancy, root growth activity (which comprises rooting and root elongation after rooting) and leaf growth activity increased gradually; the former reached a maximum in late August and the latter in mid-September. Asatsuki plants grew vigorously in September and early October. During this period the mean air temperatures are close to the optimum temperatures for growth.After reaching their maxima, both growth activities decreased; root growth activity reached a minimum in mid- or late October and leaf growth activity in mid- or late November. Thus, growth was suspended in late autumn. In early or mid-December root growth activity began to increase again and in early January leaf growth activity began to increase again. Root growth activity reached a maximum in February and leaf growth activity in mid-March. In late January some plants initiated storage leaf primordia, but the plants appeared to be in a state of imposed dormancy until early spring.Roots resumed growth in, late March but in mid-April rooting activity was lost and there was no increase in root weight per plant from mid-April onwards. Leaves resumed slow growth in early or mid-March, but vigorous growth of leaves did not occur until after the continuous snow cover had melted off (in early April). Leaf growth activity almost ceased in late May, and growth of tops ceased in late May. All storage leaf primordia were initiated by mid-April and those developed into cloves. The cloves grew rapidly from mid-April to mid-June. Browning of tops and dying of roots progressed rapidly from mid-June onwards, so that tops had almost died down by late June.Leaf and root growth activities varied considerably from month to month (except for the dormant summer months). Growth activities became extremely low during late autumn and early winter, and asatsuki plants hardly grew at any temperatures between 9 and 25°C, showing that the plants were in the state of innate dormancy. Accordingly, it is concluded that asatsuki plants fall into innate dormancy twice a year, both in summer and in late autumn or early winter. However, the late autumn (or early winter) dormancy was not so deep as the summer dormancy. It is assumed that cool temperatures in October induced the late autumn dormancy in asatsuki plants.