The water balance of fleshy fruit is heavily influenced by fruit transpiration. Transpiration is driven by the vapor pressure gradient between the fruit and the atmosphere. Stomatal closure is the main form of resistance to water loss. Thus, stomatal density (the number of stomata per unit area) and function are critical for regulating transpiration. In Northern Highbush blueberry (NHB, Vaccinium corymbosum L.), transpiration rates decline as the fruit develops. However, these dynamics remain unknown in Southern Highbush blueberry (SHB, Vaccinium corymbosum L. interspecific hybrids). This study examines the relationship between stomatal density, stomata function, and fruit transpiration rates in SHB. Three SHB cultivars were analyzed: ‘Jewel’, ‘Sweetcrisp’, and ‘Keecrisp’. Fruits were sampled weekly between petal fall and the ripe stage. Stomatal imprints were collected from six fruit regions: calyx basin, calyx, distal (calyx) end, distal middle, proximal middle, and proximal (pedicel) end. Stomatal density and distribution were quantified using StoManager, an artificial intelligence tool that uses convolutional neural networks to count and measure stomata in micrographs. Stomata density varied by genotype and fruit region. Distal regions exhibited the highest stomata densities in all varieties. No stomata were observed in the proximal middle or proximal (pedicel) end for either genotype. Fruit transpiration rates were measured using an infrared gas analyzer equipped with a custom-built chamber. Results indicated a progressive decline in transpiration rates as the fruit matured. The results suggest that SHB and NHB exhibit similar stomata morphology and transpiration patterns during fruit development.
