Abstract
It has been generally recognized that common stocks do not form flower buds at temperatures above 15.6°C. In recent years, however, many cultivars of extremely early flowering have been bred, which flower from October to December when they are sown in the beginning of August. In the previous paper, it was shown that ‘Senshonoyuki’, an extremely early flowering cultivar in Japan, flowered at 3°C- day and 25°C-night temperatures. In this paper, the effect of temperatures above 13°C on flowering of non-branching stocks was investigated.
1. Eight cultivars of extremely early flowering and medium flowering cultivars were sown in the hot bed above 15°C in March of 1972. Seedlings with 2-4 unfolded leaves were grown in glass houses under natural day length, in which minimum temperatures were maintained at 15°, 20° and 25°C. No flowering was observed at any temperatures in medium flowering cultivars. In extremely early flowering cultivars flowering percentages of ‘Christmas Rose’, ‘Senshonoyuki’ and ‘Christmas Blue’ were 100% at 25°C, and that of ‘Christmas White’ was 72%. However, the time of flower budding and flowering at 25°C were later than 15° and 20°C. The number of nodes to inflorescence increased directly in relation to the growing temperature.
2. Eight extremely early flowering cultivars and one early flowering cultivar were sown in September of 1972. Seedlings with two unfolded leaves were transferred to glass houses under natural day length, in which minimum temperatures were maintained at 13°, 18° and 23°C. Flowering percentages of extremely early flowering cultivars, ‘Christmas Rose’, ‘Akinobeni’, ‘Akinomurasaki’ and ‘Kanshio’ were 100% at 23°C, and those of ‘Benihime’ and ‘Tsukinoyosooi’ were 98%. However, those of ‘Christmas Blue’ and ‘Christmas White’ were 70% even at 18°C, and further lowered at 23°C. Flowering of ‘Zuisei’, an early flowering cultivar, were occurred only at 13°C. Differences of the times of flower initiation and flower budding at 13° and 18°C were very slight in all the extremely early flowering cultivars. However, flower initiation and flower budding of ‘Christmas Blue’ and ‘Christmas White’ were later than those of the other six extremely early flowering cultivars at these two temperatures. The higher the temperature, the more nodes to inflorescence in all the extremely early flowering cultivars. Their plant height was the lowest at 23°C and some abnormal flowers were observed above this temperature.
These results suggest that the maximum temperature, which induces flowering in most of the extremely early flowering cultivars of non-branching stocks, is 23° -25°C.
