The effects of radiation frost on freezing damage and apical abortion in calabrese (Brassica oleracea var. italica) transplants

Freezing damage has been reported to be associated with apical abortion (bl indness) in calabrese, preventing the formation of a marketable head. In th e past, laboratory based experiments studying the freezing of whole plants using convective freezing have resulted in death of the plants while failin g to induce blindness. Using a unique radiation freezing facility, capable of reproducibly simulating glasshouse frost conditions, we investigated the effect of hardening and freezing duration on calabrese transplants. Four c ultivars were raised and subjected at four different growth stages (3, 5, 7 and 9 leaves) to a factorial combination of frost (0-4 d of frost between -2 to -4 degrees C) and hardening regimes (0-6 d at 4 degrees C prior to fr eezing). Following each frost/hardening treatment, half the sample was diss ected and the remainder potted up and grown on. Light and transmission elec tron microscopy of the dissected plants revealed that the apical region of all the varieties at each of the growth stages remained intact following al l frost treatments applied. No significant apical abortion was recorded. No blind plants were recorded following a repeat of the experiment using comm ercially grown plants (cv. Marathon). It was observed that the apical regio n of the calabrese transplants has a high degree of frost tolerance and tha t freezing conditions alone are not responsible for the induction of apical abortion.