Genotypic variability in broccoli hollow stem as affected by plant density under contrasting seasonal weather conditions

Hollow stem formation can cause substantial quality and yield losses in broccoli production. This physiological disorder is closely associated with weight and stem diameter of the inflorescence. These head traits vary depending on variety and growing conditions. The objective of this study was to assess the susceptibility of different broccoli varieties to hollow stem formation under contrasting seasonal weather conditions and to evaluate increased plant density as a crop management strategy to mitigate this disorder. For this purpose, three field experiments were conducted using twelve commercially available varieties (‘Ares’, ‘Batavia’, ‘Covina’, ‘Ironman’, ‘Larsson’, ‘Malibu’, ‘Naxos’, ‘Neliam’, ‘Parthenon’, ‘SV1002BL’, ‘Triton’, and ‘Vicario’), grown at two plant densities (4.5 and 9.3 plants m -2 ) and across three seasons (early summer, summer, and fall). Vegetative growth, head traits, and the occurrence of stem cavities were evaluated. Four varieties (‘Ares’, ‘Ironman’, ‘Larsson’, and ‘SV1002BL’) exhibited low susceptibility to pith cracking, whereas three varieties (‘Batavia’, ‘Parthenon’, and ‘Vicario’) were highly affected. Under dry conditions during vegetative development, the proportion of heads exhibiting hollow stem remained below 9%, whereas it increased to 53% under warm and humid conditions. Close plant spacing markedly reduced stem and head width and almost completely suppressed cavity formation. Variety-specific threshold values for head weight and stem diameter were identified, above which the severity increased linearly. Overall, the results demonstrate that both variety choice and plant density represent effective management tools for minimizing hollow stem formation in broccoli production.