Plant canopy and root architecture characteristics play a crucial role in water uptake and plant growth. Blueberry roots are shallow and lack dense root hairs, making them more susceptible to drought than most fruit crop species. In northern highbush blueberry (Vaccinium corymbosum), differences in root size, root architecture, and root-to-leaf balance may impact drought resilience, particularly in maintaining photosynthesis (A) under limited soil moisture. However, this has not yet been examined in this species. This study evaluated drought resilience in two V. corymbosum genotypes with contrasting canopy and root architecture characteristics (Bluecrop, low root-to-leaf ratio; Draper, high root-to-leaf ratio). During the pre-drying period, both genotypes exhibited similar A and stem water potential (Ψ stem). Irrigation water was withheld to initiate drought conditions. By day 4 of withholding water, Bluecrop showed a decline in A, but its Ψ stem did not significantly change until day 6. In contrast, Draper did not show a decline in A or Ψ stem until day 6 of withholding water. Both cultivars reached a critical threshold of stomatal conductance (gs) (90% reduction from well-watered conditions) on day 10 of withholding water. Following re-watering, Ψ stem recovered immediately in both cultivars on day 2 of re-watering (day 12 of withholding water). However, the recovered Ψ stem of Bluecrop did not correspond with any increase in gs until day 14 of rewatering (day 24 of withholding water). Meanwhile, Draper exhibited a much higher gs and A than Bluecrop throughout the post-rewatering period, suggesting that Bluecrop is more sensitive to drought conditions than Draper. Post-experiment analysis confirmed that Draper had a larger root-to-leaf ratio than Bluecrop, which likely enhanced water absorption and supported faster recovery following rehydration. No significant difference in root architecture characteristics were found between these two cultivars, considering the number of root tips, root length, and surface area per root diameter at different levels (< 0.25 mm, 0.25- 0.5 mm, and >0.5 mm). These results suggest that root-to-leaf ratio and root-to-leaf hydraulic conductance play a central role in determining drought resilience in V. corymbosum genotypes. Future studies will be carried out to confirm this finding across a greater number of genotypes.
