Abstract

The low-temperature tolerance of flowers from 3 black currant cultivars, Br?dtorp, Ben Tirran and Baldwin (which together represent a large part of the available genetic base for this subgenus of Ribes), was determined at 2 stages of floral development. Plants were maintained either at 4C in a growth cabinet under a 16-h 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 was partly confirmed by the finding that detached flowers from all 3 cultivars have the capacity to supercool to at least -9C. Ice nucleation in stem tissue, however, was found to occur at or above -2C. The fact 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, indicates the presence of barriers to propagation of ice from stem tissue to raceme. Such barriers within individual racemes were also indicated by patterns of freezing damage to flowers on intact plants cooled to -5C.