Water State and Release from Dormancy in Blueberry Flower Buds

Abstract

Three blueberry (Vacciunium section Cyanococcus) genotypes, that have different chilling requirements and levels of cold hardiness, were studied. Dormancy was evaluated and water status determined, using Nuclear Magnetic Resonance, throughout the accumulation of chilling that leads to release from dormancy. Among the two highbush cultivars studied, `Bluecrop' (Vaccinium corymbosum) was the most dormant and `Gulfcoast' (Vaccinium corymbosum × Vaccinium darrowi) was the least dormant. The rabbiteye cultivar Tifblue (Vaccinium ashei) had an intermediate dormancy. From estimates of chilling requirements (CRs), it appeared that the cultivar with the deepest dormancy had the highest CR. The NMR results showed that `Bluecrop' buds had the lowest relaxation times (T2), indicating that water was relatively more bound in `Bluecrop' buds than in the buds of the two other cultivars. Whatever the cultivar, no significant variation of T2s and water content of the buds was noted throughout the accumulation of chilling, even after CRs were satisfied. On the other hand, a transition from bound to freer water occured if the plants were placed under forcing conditions (24 °C, long day) after they had received enough chilling to satisfy their CRs. The results suggested that the level of bound water was more associated with the level of cold hardiness rather than with the level of dormancy.