Responses of Commercial Olive Cultivars (Olea europaea L.) to Cold Stress Using Electrolyte Leakage Method and Measuring Total Soluble Carbohydrate

Identification and characterization of tolerant and susceptible cultivars of crop plants to cold stress is important. In this regard, in present research electrolyte leakage and Total Soluble Sugar (TSS) contents in the leaf and bark tissues in ten olive cultivars, namely, Zard, Mari, Fadak87-1, Fadak87-5, Fadak86, Fadak77, Arbequina, Mission, Blady and Coratina were measured to assess their response to cold stress during two consecutive years. Two years-old shoots from five year-old olive trees were collected in summer and winter from a commercial orchard in Qom, Central Iran and exposed to cold treatments of 0, -4, -8, -12, -16 and -20°C for 24 hours. Then LT50 was measured by electrolyte leakage. A considerable increase in cold-hardiness was observed with decreasing temperature. Leaf and bark tissues exhibited more tolerance in winter than summer and bark tissue had more tolerance than leaf in both seasons. Also TSS contents in leaf and bark tissues were greater in winter than summer and in all studied cultivars bark tissue had greater TSS content than the leaf. Results showed that cold-hardy cultivars, Zard, Arbequina and Fadak87-5 (with tolerance thresholds of -17.34°C, -17.5°C and -17.99°C, respectively) had greater TSS contents in tissues in summer and winter compared to susceptible cultivars, Coratina and Mari (with tolerance thresholds of -7.18°C and -9.13°C respectively). Although the precise mechanism in response to cold stress has not been characterized in olive tree, it can be concluded from this experiment, that the tissue TSS content is closely associated with resistance to cold stress in this tree species