Factors to consider in artificial freeze tests

To measure the development of freezing tolerance in plants it is essential to have a reliable and simple screening procedure. Also, the screening procedure must mimic the major stresses encountered e.g. prolonged freezing as experienced in the winter versus short term frosts experienced during active growth. Unless the appropriate stress is applied, the appropriate plant response will not be measured. The test should also measure the ability of the plant to repair and resume normal growth. The following will be discussed in relation to predicting freezing tolerance: methods of acclimation including light and temperature; the nature of the freezing stress applied under controlled conditions compared to the field; rate of cooling; duration of the freezing event; significance of electrolyte leakage; ice nucleation temperature; ice nucleation site; wet versus dry tissue; role of INA+ bacteria evaporative cooling; repair and regeneration factors affecting ice crystal growth and whole plants versus excised parts vs cell suspension cultures versus protoplasts as they relate to survival.