Evaluation of Freezing Tolerance of Whole Plants in Komatsuna (Brassica campestris L.) and Spinach (Spinacia oleracea L.)

Abstract

To establish a practical method to evaluate the freezing tolerance of leafy vegetables, the relationship between freezing tolerance of intact komatsuna and spinach plants, cold-acclimated at different temperatures and electrolyte leakage from leaf tissues was determined. In both komatsuna and spinach, the freezing tolerance correlated well with electrolyte leakage from leaf tissues, especially with the leaf area that was damaged by freezing during cold acclimation (i.e, high, middle and low temperature treatments). However, the temperature at which 50% of electrolytes leaked from tissues occurs (T_EL50) was consistently lower by 2 to 4°C than the temperature at which 50% of leaf area was injured. When freezing tolelance as determind by the electrolyte leakage from leaf tissues was compared with that of the whole plant, at T_EL50 almost all leaves were severely injured and recovery of plant growth was substantially delayed. Because freezing tolerance of whole plants is expressed as the temperature at which the leaves are slightly injured and recovery is not seriously affected. Consequently, the freezing tolerance of whole plants of komatsuna and spinach may best be expressed as the T_EL15 or T_EL20 (at which temperature only 15 to 20% of the electrolytes leak from leaf tissues). The maximum of 100% electrolyte leakage is obtained from ground tissues or tissues subjected to a freeze/thaw cycle to -80°C.