Estimation of Cold Hardiness in Trunk Bark and Wood Tissues of Peach Trees (Prunus persica)

Abstract

To establish the reliable methods for estimating cold hardiness for trunk tissues of peach trees, tissue browning, exotherm, electrolyte leakage (EL), and triphenyl tetrazolium chloride (TTC) analyses were performed on shoots, and bark and wood tissues of 5-year-old branches in Janghowonhwangdo and Hikawa Hakuho peach trees (Prunus persica) during cold acclimation. Visual estimation based on tissue browning was relatively simple and the discoloration caused by freezing temperatures was observed in both bark and wood tissues. However, its scoring was difficult to quantify the level of cold hardiness. Exotherm analysis was conducted to characterize freezing in shoots, and bark and wood tissues. High temperature exotherms, indicating extracellular ice formation, were exhibited consistently between −5 and −10oC. However, low temperature exotherms, indicating intracellular ice formation associated with freezing injury, were not detected. Therefore, exotherm analysis was not suitable for estimating cold hardiness in all tissues of peach trees. EL and TTC analyses provided reproducible results. These two analyses were also possible to express the level of cold hardiness as temperature representing 50% injury occurred (LT50). EL analysis required the additional processes for separating bark from wood tissues and for cutting wood tissues into small pieces prior to being subjected to freezing treatments, while TTC analysis did not require such processes. TTC analysis estimated cold hardiness lower than EL analysis, showing a tendency to overestimate cold hardiness in plant tissues. Thus, EL and TTC analyses could be recommended for estimating cold hardiness in thick branches or trunk in peach trees.