关键词: 核桃属, 休眠期, 抗寒性, 电解质渗出率, 组织褐变, TTC染色, 枝条解剖结构

Abstract: The test materials were annual dormant branches of 18 Juglans germplasms that belong to 4 species including J. regia L.，J. hopeiensis Hu.，J. mandshurica Maxim.，and J. nigra L. The semi-lethal temperatures（LT₅₀）were assessed separately by electrolyte leakage，tissuebrowning，and triphenyl tetrazolium chloride（TTC）dyeingmethod with Logistic equation. Branch anatomical structures were observed with paraffin sections. The correlations between branch anatomical structures and freezing tolerance were analyzed. The results showed that relative electrical conductivities（REC）of walnut annual branches were rising with the temperature drop. The significant differences of LT₅₀ of Juglans germplasms were observed between –38 ℃ and –22 ℃. The interspecific differences were distinct，and the order of freezing tolerance was J. nigra> J. mandshurica，J. hopeiensis > J. regia. Electrolyte leakage，tissue browning，and TTCdyeing method all could be used for assessment of the freezing tolerance in dormant period，but LT₅₀assessed by electrolyte leakage was more accurate than the other methods. There was significant positive correlation（P < 0.01）between LT₅₀ and REC at–24 ℃，which was a little higher than LT₅₀ of the most Juglans germplasms. LT₅₀ and REC at–24 ℃ could be used as physicochemical indexes for freezing tolerance identification of Juglans indormant period. In addition，thetissues thickness of annual branches with roughly similar stem diameter had significant differences. Thesignificant negative correlation（P < 0.01）was showed between LT₅₀andphellem layerthickness orphellem layer ratio in the branch，which provided morphological indexes to assess the freezing tolerance of Juglans in dormant period.

Key words: Juglans, dormant period, freezing tolerance, electrolyte leakage, tissue browning, TTC dyeing, branch anatomical structure