Endodormancy in six blackcurrant (Ribes nigrum) cultivars

The demand for blackcurrant (Ribes nigrum L.) has increased as consumers have become aware of the health effects of blackcurrant berry. New cultivars suitable for both fresh market and processing are needed. As the winter temperatures are increasing, one aim in major blackcurrant breeding programs is low chilling requirement and therefore a short endodormancy in new cultivars. However, in northern Europe a long and deep endodormancy is required, to avoid frost damaged plants after initiation of growth during warm spells in winter followed by frost. The aim of our study was to examine the depth of endodormancy and cold hardiness in six blackcurrant cultivars at different times during winter. Single shoots of the Lithuanian cultivars ‘Almiai’ and ‘Gagatai’, Finnish cultivars ‘Mikael’ and ‘Mortti’, and Scottish cultivars ‘Ben Hope’ and ‘Ben Tron’ were collected from the field in southern Finland. The depth of endodormancy was determined as the percentage of buds broken during forcing at room temperature and as time (days) to bud break. Cold hardiness (LT₅₀) was measured with controlled freezing tests by exposing the shoot samples to gradually decreasing temperatures in the freezing chamber. The effectiveness of different temperatures and light on breaking of dormancy was studied in the two Finnish cultivars. The deepest dormancy was observed in the cultivars ‘Almiai’ and ‘Gagatai’, while a more shallow dormancy was found in ‘Ben Tron’ and ‘Mortti’. ‘Ben Tron’ was also the least cold hardy cultivar in our freezing tests, while ‘Almiai’ was very cold hardy. The effectiveness of temperatures 0, +6, +12 and + 18°C in breaking of endodormancy was studied under controlled conditions in shoots of ‘Mikael’ and ‘Mortti’. In both cultivars, the most effective chilling temperature was 0°C.