Changes in Morphological Traits Under Hypoxic Conditions in Broccoli Cultivars with Different Waterlogging Tolerance

Abstract In our previous study, sensitive broccoli cultivars exhibited adverse effects on head yield after just 3 days of waterlogging. Mature plants of sensitive cultivars show severely reduced water content under waterlogging stress. This phenomenon suggests a strong correlation between impaired water uptake under waterlogged conditions and broccoli tolerance to such conditions. In this study, the relationship between these factors was assessed by focusing on the root system, using a primarily morphological approach in three characteristic cultivars, and comparing changes in biomass, water content, root length, internal root structure, and hydraulic conductivity under hypoxic conditions (AIR−). Hypoxia caused by hydroponic cultivation without aeration reduced shoot biomass and substantially increased the shoot-to-root dry weight ratio and leaf area-to-root dry weight ratio in the sensitive cultivars ‘Sawayutaka’ and ‘First Star’. The interaction between aeration and cultivar affected internal root structure but, not root length, radial barriers to oxygen loss, or lignin and suberin deposition. Hypoxia reduced xylem area in the roots of the sensitive cultivars but not in the tolerant ‘Shigemori’. Moreover, the tolerant cultivar maintained high hydraulic conductivity under hypoxic conditions. These results suggest that maintaining root xylem size and hydraulic conductivity, even under hypoxic conditions, may enhance broccoli tolerance to waterlogging.