Day length and temperature interactively influence flower bud initiation in blueberry (Vaccinium corymbosum interspecific hybrids) plants. When days are short and temperatures are low, blueberry plants initiate flower buds rather than vegetative buds. Night interruption and/or warmer temperatures limit flower bud initiation. Once differentiated, flower buds enter endodormancy, restricting reproductive development to specific times of the year. Some genotypes in the University of Florida Blueberry Breeding and Genomics program have been observed to bloom in the middle of the summer under long days and warm temperatures. To investigate this phenomenon, we conducted a controlled-environment experiment to assess flower bud initiation and dormancy responses in a summer-blooming genotype, ‘FL16-64’, compared to the standard southern highbush cultivar ‘Arcadia’. Plants were grown in growth chambers with factorial combinations of temperature and photoperiod treatments. Temperature regimes mimicked Florida field conditions: warm (28 °C day / 20 °C night) and cool (18 °C day / 10 °C night). Photoperiods included short (8 hours), neutral (12 hours), long (16 hours), and interrupted (8 hours 1 hour of night interruption) day lengths. There were 6 plants of each genotype per temperature-photoperiod combination. Results showed that warm temperatures promoted vegetative growth in both genotypes. ‘Arcadia’ developed flower buds primarily under short days and cool temperatures, and these buds entered endodormancy after differentiation. In contrast, ‘FL16-64’ initiated flower buds across all temperature and photoperiod treatments. Moreover, flower bud development was enhanced under warmer temperatures and neutral day lengths. Notably, these buds bypassed dormancy and progressed directly to bloom. These findings indicate that ‘FL16-64’ exhibits day-neutral flower bud initiation and some of its flower buds lack endodormancy, characteristics consistent with an everbearing growth habit. Everbearing blueberry genotypes could be used to produce blueberries during the domestic off season in Florida.
