Influence of Vegetative Growth and Head Traits on the Hollow Stem Formation in Broccoli Affected by Cultivation Factors

Stem hollowness is a common disorder in broccoli, often reducing marketable yield. This study analyzed factors influencing its development and identified agronomic strategies for mitigation. Three field trials with the varieties ‘Parthenon’ and ‘Naxos’ investigated the effects of plant density, soil mineral nitrogen supply, and foliar boron application on plant growth, head characteristics, and hollow stem development. The proportion and severity of hollow stems were significantly affected by variety, plant density, and nitrogen supply. Increasing plant density markedly reduced the disorder, with symptoms nearly absent at close spacing. ‘Parthenon’ showed high susceptibility at wide spacing, showing 30–70% incidence depending on nitrogen supply, whereas ‘Naxos’ exhibit only 1–28%. Foliar boron application had no effect. The cavity formation correlated closely with head traits and varied with cultivation and weather conditions. Hardly any hollow stems occurred at stem diameters below 3.3–4.4 cm and head weights below 330–447 g. Above these values, the severity of damage increased linearly with increasing stem diameter (R2 = 0.78–0.93) and head weight (R2 = 0.74–0.84). Vegetative growth had only a minor influence. Overall, stem hollowness is mainly linked to head traits, with variety and plant density being the most effective factors for its reduction.