Competitive biomass allocation between the main shoot and lateral branches of Broccoli (Brassica oleracea L. var. Italica)

Abstract

The branching habit and stalk proportion of heading type broccoli (Brassica oleracea L. var. italica) differs based on the cultivar, but the extent of the effects of these factors on the apical head weight is unknown. The main objectives of this study were to elucidate the relationships between the apical head weight and the branching habit or the stalk proportion. Firstly, the shoots of broccoli from six cultivars were divided into four parts (apical head, leaves on the main stem, lateral branches, and the rest of the main stem), and the weight proportions of each part were investigated. The results showed that the cultivars showing higher branching tended to produce smaller apical heads. Furthermore, apical head weights showed a positive relationship with the area of the leaves on the main stem, but a negative relationship with those on the branches. Secondly, four cultivars were grown with lateral bud nipping. This significantly increased the apical head weight in the cultivars showing higher lateral branching, but did not significantly change the weight of the whole shoot. These results suggest competitive biomass allocation between the main shoot and lateral branches. The difference in the weight of lateral branches depended on the probability of axillary bud presence rather than on the number of internodes or weight per branch. Finally, a strong correlation between the apical head weights and the square of the stalk diameter was demonstrated by generalized linear models (R2 = 0.95). These findings will contribute to the knowledge base on diverse methods of broccoli cultivation.