Enlarging Broccoli (Brassica oleracea L. var. italica) Heads by Extending the Growing Period and Sparse Planting to Increase Floret Yield

Abstract

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.