On the flower head formation and development of cauliflower plants. I

The present experiment was conducted from 1959 to 1961 to obtain the fundamental data on the flower head formation and development of cauliflower plants. The following was noted.1. It was suggested from the relations between the sowing time in spring and summer and the growth behavior of various cauliflower varieties that the highest yield was obtained by vigorous vegetative growth for more than 95 days with Early Snowball A, 100 days with Nozaki-wase and Italian broccoli (De Cicco), 110 days with Masuda-nakate and 130 days with Masuda-bansei at average temperatures above 20°C. Also shown was that the flower head developed well at 15° to 18°C for 55 days with Early Snowball A, and 25 days with Nozaki-wase and Italian broccoli.Comparing with the ideal pattern mentioned above, both number of days to flower bud induction, and the duration of head development were shortened owing to the temperature in spring and summer when the seeds were sown in early spring, whereas in the case of late summer sowing, the flower bud differentiated with shorter duration of vegetative growth, followed by the longer duration of head development depending on cold temperature in autumn.2. Phytotron experiment showed that the earliness of flower bud induction was affected with temperatures, plant sizes and varieties of cauliflower plants. The larger the plant size, the shorter the chilling requirement for flower bud differentiation.The most sensitive variety to the low temperature was Early Snowball A, followed in decreasing order by Nozaki-wase, Italian broccoli, Masudanakate and Masuda-bansei.It was considered that the maximum critical temperature which induces florwer bud was 25°C for Early Snowball A and Nozaki-wase, and 20°C for Italian broccoli, and that the minimum was 5°C for all of them. It was further suggested that the optimum temperature for induction of flower bud was 13°C with Early Snowball A and it was lower with medium and late varieties.The low temperature treatment for 10_??_15 days following flower bud induction was required for normal head development, though number of days required varied with plant sizes and varieties.Leafy head was induced by shortage of the low temperature stimulus. Daily interposal of higher temperature enhanced the low temperature requirement for flower bud differentiation and normal head development.3. It was clearly shown that the seed vernalization promoted flower bud induction when it was partially supplemented with plant vernalization in Sakata-gokuwase, Nozaki-wase and Italian broccoli.