Low-temperature Tolerance of Blackcurrant Flowers

Abstract

The low-temperature tolerance of flowers from three blackcurrant (Ribes nigrum L.) cultivars, `Brödtorp', `Ben Tirran', and `Baldwin', was determined at two stages of floral development. The three cultivars together represent a large part of the available genetic base for this subgenus of Ribes. Plants were maintained either at 4 °C in a growth cabinet under a 16-hour photoperiod or outdoors in Scotland during Spring 1997. Observed genotypic differences in survival were not associated with differences in LT50 of the flowers, and observations of freezing damage to flowers on intact plants suggest that the flowers can often survive by supercooling. This hypothesis is partly confirmed by the finding that detached flowers from all three cultivars have the capacity to supercool to at least –9 °C. Ice nucleation in stem tissue, however, was found to occur at or above –2 °C. That flowers on intact plants can apparently survive by supercooling, together with the finding that ice nucleation in stem tissue occurs at temperatures well above the LT50 of flowers, indicate the presence of barriers to propagation of ice from stem tissue to raceme. Such barriers within individual racemes are also indicated by patterns of freezing damage to flowers on intact plants cooled to –5 °C.