2018 年 87 巻 4 号 p. 508-515
Lateral heads, which generate after the harvest of an apical head of broccoli (Brassica oleracea L. var. italica), are generally small and have a low market value. Our purpose in this study was to increase the yield of broccoli from April to May, when domestic broccoli production is low, by removing excess branches (dubbed the “L-shaping” process) and growing one or two large and marketable lateral heads with the cultivar ‘Yumehibiki’. First, we demonstrated that transplanting seedlings in late-January and early-February to a field covered by plastic mulch and tunnels enabled apical heads and marketable lateral heads to be harvested in April and May, respectively. The number of marketable lateral heads reached a maximum 81% of that of apical heads. Next, we derived the base temperature (BT; °C), effective heat unit summation (EHUS; °C·day) from transplanting to apical head harvest, and additional EHUS from apical head harvest to lateral head harvest. They were 1.76°C, 747°C·day, and 254°C·day in 2016, and 1.74°C, 675°C·day and 204°C·day in 2017, respectively. The favorable timing for transplanting to result in the highest marketable yield was estimated as when the average temperature reached 4.0°C, but was less than 7.1°C. Finally, we characterized the lateral branches that were most likely to produce marketable lateral heads. The branches that produced marketable heads showed significantly higher values for thickness of branch, length of branch, and number of leaves on branch than those that produced nonmarketable heads, although the diameters of the developing heads on the branches were not significantly higher. Further analysis revealed that the leaf area was also significantly higher in marketable lateral heads than in nonmarketable heads. Taken together, the possibility of a substantial increase in yield during the broccoli off-crop season by using L-shaped ‘Yumehibiki’ was demonstrated in this study.
