Seasonal variation in the competence of the buds of three cultivars from different Citrus species to flower

The role of bud competence in the determination of flowering seasonality was studied in three Citrus cultivars, Bearss lime (Citrus latifolia Tan.), Fino lemon (C. limon [L.] Burm. f.) and Owari satsuma (C. unshiu (Mak.) Marc.), which differ in their adaptation to hot climates and their propensity to produce off-season blooms. Potted plants were kept in a greenhouse under non-inductive conditions (minimum temperature higher than 20 degrees C), and periodically the flowering response was determined of a group of trees exposed for 30 days to an inductive temperature regime (15/8 degrees C). A seasonal change in bud competence was demonstrated, and both bud sprouting and flower formation were highest when the low temperature regime was imposed during February and March. During the summer months, the low temperature regime resulted in a small increase in bud sprouting as compared to non-chilled trees, but only vegetative buds developed and no flowers were formed. The influence of environmental factors on the determination of bud competence was further studied. No effect of photoperiod was found, but raising the minimum air temperature above 25 degrees C during 60 days, eliminated bud competence in Owari satsuma. In Bearss lime trees, the buds reacquired the competence after 4 months at 25/20 degrees C, a temperature regime that does not induce flower formation. The reacquisition of competence was much faster at a lower temperature (15/8 degrees C). A consistent relationship between the flowering response and DNA methylation in buds could not be demonstrated in all cultivars.