Studies on the floral differentiation and fruiting in Brassica chinensis cultivar To-pe-tsai

Abstract

A kind of chinese cabbage named To-pe-tsai (Brassica chinensis cultivar To-pe-tsai) is one of the most common vegetables in Formosa. It′s reproductive behavior appears to depend upon a lower temperature.
This study was designed to secure the effects of temperature and daylength on the flowering and fruiting of To-pe-tsai.
Experimental items were as follows:
1) Studies on the capacity to respond to the temperature at 10°C after germination. The ages of young seedling exposed to a low temperature were as follows: (a) the one having the main root, 1 mm long, (b) the cotyledons fully expanded, (c) the 1st leaf, 2cm long, (d) the 2nd leaf, 2cm long.
2) Effect of daylength after chilling of seedling on flowering behavior. Plants were first exposed to a temperature of 4°C for 3 days, followed by an exposure to a sufficient number of days of 8hr daylength or natural daylength of 15 to 16hr.
3) Effect of an insufficient chilling on flowering behavior. Plants were chilled at 10°C for 24, 48 and 72hrs, and then grown under constant temperature of 23°C.
4) Effect of various temperature on flowering behavior after chilling. After sufficient chilling at 4°C in dark room, plants were grown under different constant temperature of 15, 23 and 30°C in Phytotron.
The results obtained were as follows:
1. When the plants are exposed to 10°C for 3 days at the age of 12 days (1st leaf, 2cm long) after sowing, followed by the exposure to high temperature of 23°C, together with 15 hr-daylength, they can proceed most rapidly, about 10 days, to flower bud differentiation and bolting, and come in to flower after 30 days.
2. After chilled at 4°C, the bolting and flowering of plants is promoted by the long day treatment, and is delayed by short day treatment.
3. The plants form an abnormal flowers both in the case exposed to insufficient chilling or grown at high temperature after complete chilling.
4. The characteristics of an abnormal flower are as follows: (a) the size of abnormal flower is smaller than the one of a normal flowers, (b) the petales and normal pollens are always absent, but the stamens and stigma grown relatively large, (c) the internode length of two flower stalks is extremely short, so the flowers grow together and sometimes the inflorescence fasciates on the base part of flower stalks, (d) the flower buds become black and wither, and then fall off before anthesis, (e) the fruiting does not occur normally.