Endodormancy and paradormancy in the raspberry cultivar 'Glen Clova'

The relationship between endodormancy, (winter dormancy) and paradormancy, (apical dominance) was investigated in the raspberry cultivar 'Glen Clova' in order to evaluate the potential for manipulation to improve bud break in protected crops. Intact raspberry canes, and canes which had either been trisected or divided into single nodes were forced after increasing amounts of chilling. The results showed that bud break was significantly increased in the single nodes regardless of their origin on the cane. The buds on the lower and middle sections of the trisected canes also showed higher levels of bud break than the buds from the equivalent areas on the intact canes after the accumulation of more than 1000 chilling units (hours at 4 degrees C). A consistently higher level of bud break was observed in the buds on the upper region of the intact canes than in the buds from the middle and lower regions of the same canes. The buds from the lower region of the intact canes showed the lowest levels of bud break. These results indicated that following the period of deep endodormancy, raspberry buds enter a transitional phase during which growth inhibition due to endodormancy is progressively replaced by growth inhibition caused by paradormancy. Results are discussed which suggest that manipulating the cane to reduce paradormancy would improve the bud break of raspberry canes under conditions of insufficient chilling. Such manipulations might include tip removal or horizontal training methods.