Assessment of frost damage to leafless stem tissues of Quercus petraea: A reappraisal of the method of relative conductivity

Leafless Quercus petraea stems 1.4–5.0 mm in diameterwere exposed to freezing temperatures before assessing frostdamage visually and by two methods where electrolyte leakagefrom tissues was examined. Visual assessment could not discriminatelethal from non-lethal damage, whereas electrolyte leakage could.Assessments based on the rate of electrolyte leakage took almosttwice as many man hours to obtain, but were more consistentthan those produced using the method of relative conductivity.Full equilibration of electrolyte leakage following exposureto freezing temperatures required at least 5 days at 4°C. Autoclaving the tissues at 121°C for 15 min failed to releaseall diffusible electrolytes even after 10 days equilibration,but complete release was achieved 24 h after autoclaving for120 min. Unless full equilibration is achieved, it is impossibleto define a value of relative conductivity that is indicativeof lethal damage. The use of predefined lethal values of relativeconductivity is inad visable because the relative conductivityof undamaged (unfrozen) shoots varies substantially with thephysiological state of the tissues. Allowing 5–7 days after freezing to permit full electrolyteequilibration, followed by autoclaving for 90–120 minat 121°C and allowing 24 h before measurement provides areliable method for assessing freezing injury by the methodof relative conductivity in small pieces of leafless stem tissues.Differences between treatments can then be assessed using standardstatistical procedures.