Studies on Thermal Conditions of Curd Formation and Development in Cauliflower and Broccoli

I. Effects of Low Temperature Treatment of Seeds

Abstract

Effects of low temperature treatments of seeds on curd formation and development were investigated, using several cultivars of cauliflower and broccoli, in temperature-controlled and field conditions.
1. Cauliflower plants, ‘Nozaki-wase’, of the 7th or 8th leaf stage were vernalized. Curds were formed at 15°C and 30 days after the start of growing but not formed at 20°C and 25°C until 48 days.
2. After the germinated seeds were chilled at 0°C in the dark for 30 days, cauliflower plants, ‘Nozaki-wase’ were grown at the constant temperatures of 15°, 20° and 25°C. Curds were formed at 20°C in plants when seeds had been chilled, but not in plants when seeds had not been chilled. Therefore, the germinated seeds could be vernalized with the low temperature treatment. There was no effect of chilling treatment of seeds on curd formation at 15°C, where plants formed curds regardless of chilling of seeds, and at 25°C, where plants did not form curds even with chilling of seeds.
3. Under field conditions, the time of curd formation and maturation of seven cultivars of cauliflower, differing in time of maturation, and one cultivar of broccoli was promoted hardly at all with the low temperature treatment of seeds.
4. As the treatment was lengthened, however, the number of leaves from cotyledon to curd and the stem length at curd maturity decreased in all of the cauliflower cultivars. Those of broccoli also slightly decreased.
5. Curd weight and diameter of the cauliflower were slightly inhibited, as the treatment was lengthened, but those of broccoli were promoted. In broccoli, weight and number of lateral flower heads per plant were also promoted with the longer treatment.