Browsing by Subject "”umbrella bloom” -ilmiö"

Efforts to cultivate American cranberry (Vaccinium macrocarpon Ait.) across Finland have not been successful. Even Helsinki is located north (60 ºN) as compared to the main production area of cranberry in North American (39-48 ºN), which causes challenges with cold and frost resistance, as well as with overwintering and low heat sum. Recent research has shown that cranberry could possibly survive in the conditions of Southern Finland. Low temperatures around 0 ℃ break endodormancy during winter. The aim of this research was to find out how growing site affects the dormancy release in four cranberry cultivars, and whether inadequate chilling causes ”umbrella bloom” growth, where the plant blooms but does not grow vegetatively. Samples were taken every fourth week during winter and the depth of dormancy was measured by observing the growth of terminal buds in a greenhouse. In addition, the effect of chilling temperature (-3, +2 and +7 ℃) and duration (8, 10 ja 12 wk) of chilling in controlled condition on the growth of terminal buds of cv. Pilgrim were studied. Under natural chilling conditions, the plants which had grown in a high tunnel during the growth season, needed more chilling units (CU) to achieve normal growth (2755 CU) than the open field growth plants (853-1525 CU). The chilling units accumulated every hour when T < +7 ℃. The amount of normally flowering terminal buds increased with increasing chilling duration. Same time, the amount of ”umbrella bloom” flowering decreased, which refers to the role of inadequate chilling in ”umbrella bloom” flowering. When the plants were chilled under controlled conditions (temperatures +7 ja +2 ℃), chilling units were accumulated more efficiently which caused dormancy release earlier than under natural conditions. Chilling under controlled conditions in temperature -3 ℃ is not recommended because the plants dried up too much. In conclusion, natural chilling in Helsinki (60 ºN) is sufficient for breaking dormancy in American cranberry. Recommendations for chilling cranberry under controlled conditions are in temperature of +2 ℃ for 10 weeks.