The demand for broccoli (Brassica oleracea L. var. italica) is rapidly growing in Japan, and a new production system to increase broccoli yield is required. During processing, broccoli florets are separated from the head, and floret yield may be increased by enlargement of heads beyond existing retail standards. Therefore, we conducted four cultivation tests over two years and investigated floret yields of 10 cultivars during spring and autumn cropping. We sought to identify high-yielding cultivars when the heads are enlarged via either an extension of the cultivation period or sparse planting. In the control plots, the broccoli heads were harvested at approximately 12 cm in diameter, following normal retail standards. In the extended plots, the cultivation period was extended to the limits of marketable quality. The plant density of these two plots was 3,125 plants per 10 a. In the sparse plots, plant density was half of the other plots, 1,563 plants per 10 a, and the heads were enlarged and harvested as in the extended plots. The floret yield of the control plots was 560-958 kg/10 a, and the floret yield of the extended plots was 905-2,504 kg/10 a. Head diameter of the extended plots was 15-21 cm. In the sparse plots, head diameter was 15-25 cm, and the fresh weight of the florets tended to increase, but floret yield was only 657-1,870 kg/10 a, due to the half number of plants. Across seasons and years, the 'Grandome' cultivar had consistently high yields, suggesting that it is suitable for enlarged harvesting. Compared to the 'Pixel' cultivar, the photoassimilates of 'Grandome' were more concentrated in the main shoot due to the fewer side shoots. Moreover, there were several immature floral shoots in the head of 'Grandome' at 12 cm diameter, which may explain the large size. The harvest index also increased with broccoli head size, so the large head production system enabled more efficient production and increased floret yield compared to conventional cropping methods.

The demand for broccoli (Brassica oleracea L. var. italica) is increasing for use as fresh produce and for use in the processing industry. Therefore, growth prediction technology is required for its stable production. In this study, several cultivations of experiments were conducted to clarify the critical characteristics of the parameters needed to predict the growth of broccoli in a dry matter production model. The extinction coefficient was determined based on the leaf area index and intercepted solar radiation rate. Radiation-use efficiency was demonstrated using a linear function of the accumulated solar radiation intercepted amount and the total dry weight above-ground. The distribution of dry matter to the head and stem was indicated by the sigmoid function of the accumulated average temperature. The dry matter percentage of the leaf, dry matter percentage of the head and stem, and the ratio of leaf area to the fresh weight of the leaf were represented by a power function with dry weight above-ground. The fresh weight above-ground (R 2 = 0.92) and the fresh weight of the head and stem (R 2 = 0.98) were highly correlated with the estimated and observed values. Verification was performed using the developed growth model. As a result, the error between the harvest date and the predicted harvest date could be forecasted to within 4 days and the error in the fresh weight of the head could be predicted with an accuracy of −0.3 ~ +7.7 g•plant −1 .

In Japan, broccoli (Brassica oleracea L. var. Italica) is primarily harvested manually. Some Japanese broccoli cultivars have short stems, but these broccoli heads are more difficult to harvest, and complicate the introduction of mechanical harvesters. Therefore, research is focused on strategies to control stem length. The present study examined the effects of the plant hormone gibberellin (GA) on the morphological and agronomic traits of broccoli shoots. The broccoli cultivar 'SK9-099', widely distributed in Japan and characterized by a short stem, was studied. These experiments were conducted over three cropping seasons, i.e., spring (Exp. 1), summer (Exp. 2), and fall (Exp. 3), with four GA treatment plots at 0 ppm (Control), 20 ppm, 100 ppm, and 500 ppm. This study observed that, on average, GA elongated stem length from approximately 16.0 cm in the control plot to 24.7 cm in the 500 ppm plot for the three cropping seasons, without decreasing yield. In addition, GA treatment accelerated apical bud growth and shortened the overall growth period by 16 days in the 500 ppm plot compared to the control in the fall, equivalent to 20.5% of the growth period from transplantation to harvest in the latter. This study highlights several practical benefits of GA application for growers, minimizing manual harvesting labor, avoid the difficult of designing mechanical harvesters for short-stemmed cultivars, and increase field usage efficiency by shortening the growth period.