THE FREEZING CHARACTERISTICS OF CAULIFLOWER CURD

Cultivar differences in frost resistance and the heritable nature of r esistance were demonstrated using seedling cauliflower plants. Such cu ltivar differences were not however expressed in the curd. Selection f or frost resistance in cauliflower should therefore use whole plant sc reening techniques. Curd material when frozen as isolated florets, sup ercooled over the range -1 degrees C to -12 degrees C and the mean fre ezing point of all curds tested was -6 degrees C to -7.25 degrees C (o verall mean -6.44 degrees C). Curd florets which supercooled but did n ot freeze were completely undamaged, whereas freezing always led to ce ll damage and death observed as water-soaking of the floret surface an d measured using an electrical conductivity method. The large range of freezing points measured suggests a range of active ice nucleators ei ther on or within the florets. When curds were frozen intact the abili ty of florets to supercool was severely restricted which was attribute d to the seeding of freezing by the internal growth of ice crystals. A crop protection strategy needs to identify and control or modify warm temperature nucleators in cauliflower curd.