2019 Volume 88 Issue 3 Pages 364-372
Axillary buds of broccoli (Brassica oleracea L. var. Italica) develop and produce lateral heads after the apical heads have been harvested; however, lateral heads are not used because of their small size, and only one apical head is generally harvested from one plant. In this study, we aimed to establish a new method to harvest two heads of 12 cm diameter from a plant by pinching the apical bud and growing two axillary buds (“V-shaping” process) in autumn cropping. First, we measured the probability of axillary bud generation (PA) at each leaf axil and calculated the integration of the PA (IPA). The PA from the 5th to 8th true leaves was especially high, and the IPA reached 4.7. Next, we investigated the period of harvest and yield of heads at different times (3rd, 5th, 7th, 9th, 11th, 13th, and 15th leaf stage) of V-shaping in Field 1 (Ibaraki Prefecture, Tsukuba City). In V-shaped plots from the 7th to 11th leaf stages, the number of marketable heads significantly increased in comparison to that of the control. It increased by 61% of that of the control at the 11th leaf stage. However, the period of harvest was delayed, and the quality of heads deteriorated by cold injury when V-shaping was conducted from the 11th stage onward. Finally, we assessed the applicability of V-shaping cultivation in other fields. V-shaping was conducted from the 9th to 11th leaf stage. The number of marketable heads increased by 69 and 62% in Field 2 (Ibaraki Prefecture, Tsukubamirai City) and Field 3 (Nara Prefecture, Uda City), respectively. However, it only slightly increased in Field 4 (Mie Prefecture, Tsu City). Comparison of cultivation conditions at these 4 fields revealed that early transplantation, to allow an approximate 300°C·day increase in effective heat unit summation for harvesting before the daily minimum temperature fell below approximately 0°C, was important. In addition, improving the drainage of the field seems important, and the input of manure compost (long-term fertilizer effect) may improve the quality and yield of heads. Thus, we concluded that V-shaping cultivation enabled the harvesting of two heads by V-shaping and increased the number of marketable heads by more than 60% in a wide area.