Effects of foliar application of CaCl<sub>2</sub> / SA / EBR on cold resistance of <italic>Choerospondias axillaris</italic> seedlings

<bold>Objective</bold> The effects of spraying calcium chloride（CaCl₂），salicylic acid （SA）and 2，4-epibrassinolide （EBR）on the cold resistance of <italic>Choerospondias axillaris</italic> seedlings are investigated，and the treatment and concentration of enhancing the cold resistance of seedlings are screened out to provide a basis for enhancing the cold resistance of <italic>C. axillaris</italic> seedlings to low temperature in winter or late spring cold snaps. <bold>Method</bold> Using one-year-old potted seedlings of <italic>C. axillaris</italic> derived from seeds as the experimental materials，a randomized block experimental design was adopted.From November 10th to 20th，the seedlings of <italic>C. axillaris</italic> in three experimental plot groups were respectively subjected to foliar spraying of CaCl₂（C1，C2，C3），SA（S1，S2，S3）and EBR（B1，B2，B3）six times（once every two days），and then the seedling branches of each spraying treatment were treated with low temperature stress at 4 ℃ for 12 h.The anatomical structure of the leaves after stress treatment was observed by paraffin section method，and the changes of physiological indexes of the branches were measured. <bold>Result</bold> Compared with spraying water（CK），the cell density of palisade tissue in leaves of <italic>C. axillaris</italic> increased after spraying CaCl₂，SA and EBR.Among them，the upper epidermal thickness was the largest in the treatment of 10 mmol/L SA.The thickness of the lower epidermis treated with 1 mmol/L CaCl₂ was the largest，and the palisade tissue treated with 0.1 mg/L EBR was thicker.Under the treatment of 10 mmol/L CaCl₂，the thickness of sponge tissue，leaf thickness and leaf porosity increased，and the ratio of palisade tissue to spongy tissue and leaf tightness decreased.After spraying 20 mmol/L SA，the relative conductivity content in the stem of <italic>C. axillaris</italic> was significantly lower than that of CK，which was 12.07%.The content of malondialdehyde after 0.1 mg/L EBR treatment was lower than that of other treatments and CK，which was only 0.039 μmol/g.In addition to spraying 0.01 mg/L EBR and 0.1 mg/L EBR，the soluble sugar content in the stem of <italic>C. axillaris</italic> was slightly higher than that of the control，and the soluble sugar under other treatments was reduced to varying degrees compared with the control.Compared with CK，after spraying CaCl₂，SA and EBR，the contents of soluble protein and proline（except 1 mg/L EBR）and the activities of SOD and POD（except 10 mmol/L CaCl₂）in the stems of <italic>C. axillaris</italic> were increased by varying degrees.Through the principal component analysis of leaf anatomical structure index and physiological index，the treatment effect of three different exogenous substances from strong to weak was 10 mmol/L SA，1 mmol/L CaCl₂，20 mmol/L CaCl₂，1 mmol/L SA，10 mmol/L CaCl₂，20 mmol/L SA，0.1mg/L EBR，0.01 mg/L EBR，1 mg/L EBR，CK. <bold>Conclusion</bold> The treatment of three different exogenous substances is beneficial to enhance the cold resistance of <italic>C. axillaris</italic> seedlings.The effect of SA treatment is better than that of CaCl₂ and EBR，and the cold resistance of <italic>C. axillaris</italic> treated with 10 mmol/L SA is the best.