Application of two electrical methods for the rapid assessment of freezing resistance in Salix eriocephala

The importance of early selection of frost-resistant Salix clones makes it desirable to select a rapid and accurate screening method for assessing freezing resistance among several genotypes. Two electrical methods, stem electrical impedance to 1 and 10 kHz alternating current, and electrolyte leakage of leaf tissue, were evaluated for detecting freezing resistance on three North America Salix eriocephala Michx., clones after subjecting them to five different freezing temperatures (−1,−2,−3,−4, and −5°C). Differences in the electrical impedance to 1 and 10 kHz, and the ratio of the impedance at the two frequencies (low/high) before and after the freezing treatment (DZlow, DZhigh, and DZratio, respectively) were estimated. Electrolyte leakage was expressed as relative conductivity (RCt) and index of injury (IDXt). Results from the two methods, obtained two days after the freezing stress, showed that both electrical methods were able to detect freezing injury in S. eriocephala. However, the electrolyte leakage method detected injury in more levels of freezing stress (−3,−4, and −5°C) than the impedance (−4, and −5°C), it assessed clonal differences in S. eriocephala freezing resistance, and it was best suited to correlate electrical methods with the visual assessed freezing injury. No significant impedance or leakage changes were found after the −1 and −2°C freezing temperatures.