WATER STATUS IN RELATION TO MAINTENANCE AND RELEASE FROM DORMANCY IN BLUEBERRY FLOWER BUDS

Three blueberry (Vaccinium section Cyanococcus) genotypes, that have d ifferent chilling requirements and levels of cold hardiness, were stud ied. Depth of dormancy was evaluated and water status was determined, using nuclear magnetic resonance (NMR), throughout the accumulation of chilling that leads to release from dormancy. Among the two highbush cultivars studied, 'Bluecrop' (Vaccinium corymbosum L.) was the most d ormant and 'Gulfcoast' (Vaccinium corymbosum L. x Vaccinium darrowi Ca mp) was the least dormant. The rabbiteye cultivar 'Tifblue' (Vaccinium ashei Reade) had an intermediate dormancy. It appeared that the culti var with the deepest dormancy had also the highest chilling requiremen t (CR). The NMR results showed that 'Bluecrop' buds had the lowest rel axation 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 ns and water content of the buds was noted throughout the accumulation of chilling, even after CR s were satisfied. Within 1 day of forcing (24 degrees C, long day), th ere was a shift towards freer water but no change in the mater content . Forcing was ineffective in freeing water until the plants received e nough chilling to satisfy their CRs.