Endodormancy and required chill units for raspberry canes of four raspberry cultivars

Our research examines the number of chilling hours needed for bud break of four red raspberry cultivars. Based on the measurements of open field cultivation, the canes received 50 h of temperature below 7 degrees C. After collecting the rooted shoots in October, the samples were kept at 7 degrees C in a cold room for different time periods. This process was followed by greenhouse forcing. Samples were collected for forcing each week during the 11 week chilling treatment. The examined cultivars were 'Fertodi aranyfiirt', 'Fertodi rubina, 'Fertodi zamatos', and 'Willamette'. The required chill treatment for 'Fertodi aranyfiirt' was 550 h while that for 'Fertodi zamatos' was 720 h. After the plants received this amount of chilling, most of the buds expanded and green tissues emerged when placed in warm temperatures. Further chilling treatment resulted in slight improvement of bud break, whereas for 'Fertodi zamatos', longer chilling treatment enhanced the bud breaking among the poorly developed 3-5 buds under the tip. Chilling treatment affected 'Willamette' and 'Fertodi rubina' differently. After receiving low temperature for 5 weeks (880 h), just a third of the buds of 'Willamette' expanded. The buds of 'Fertodi rubina' sprouted only at the cane's apical part (the top 1-6 bud), while the rest of the buds remained in dormancy even after the longest treatment.