Abstract:

During the extreme low temperature period of January 2016, cold resistance of 38 cacao germplasms were evaluated in Wanning, Hainan. According to the damage degree of cacao pods and leaves after low temperature, five grades were distinguished among the cacao germplasms. Using the selected cold resistance difference germplasms INA-t5 (grade Ⅰ), COM-e8 (grade Ⅱ), ECU-ev6 (grade Ⅳ) and THA-o6 (grade V), leaves anatomy and physiological responses of the cacao plants were studied after 4 ℃ low temperature treatment. Under low temperature stress, INA-t5 and COM-e8 showed obvious cold-tolerance over THA-o6 and ECU-ev6, and the damage degree of the leaves was significant. It was negatively correlated between cold resistance and malondialdehyde, proline content in cacao leaves. The protective enzyme systems of THA-o6 and ECU-ev6 were gradually destroyed in low temperature stress for 48 h, while the enzyme system of INA-t5 and COM-e8 were still active. It meant that the cold resistance of INA-t5 and COM-e8 was stronger than that of THA-o6 and ECU-ev6. The antioxidant enzyme activity, osmotic substances content and cold-resistance difference germplasm could be used for cold-resistant breeding and molecular mechanism investigation.

Key words: cacao germplasm, identification and evaluation, cold resistance, enzyme activity