Physiological mechanisms of resistance to cold stress associated with 10 elite apple rootstocks

A study was conducted in attempting to identify the cold-resistant apple rootstocks and to establish a comprehensive evaluation system. In this study, 10 elite apple dwarfing rootstocks (GM256, JM7, M26, M7, SC1, SH1, SH38, SH6, M9, and T337) were employed for the experiment and the following parameters were investigated under different low temperature stress conditions (0, −15, −20, −25, −30, and −35°C): the changes of the relative electrical conductivity (REC), anthocyanin content, protein content, soluble sugar content, soluble starch content, proline content, malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, and peroxidase (POD) activity of the dormant branches. The inflection temperature that could represent the plant tissue semi-lethal temperature (LT50) was obtained by the measurements of REC. The LT50 was used to evaluate eight other indices. The results showed that there was no significant correlation between LT50 and POD activity as well as between the soluble sugar, protein and proline contents at 0 and −15°C. Soluble starch content at 0 and −15°C and anthocyanin content at −15-(−30)°C were significantly but negatively correlated to the LT50 and the MDA content at 0-(−20)°C was significantly positively correlated to the LT50. Statistical analysis based on principal component analysis and LT50 showed that cold resistant apple rootstocks in the decreasing order from high to low as GM256, SH6, SH38, SH1, SC1, M26, M7, JM7, T337, and M9.