Assessment of the Frost Resistance in Some Olive Cultivars Using Visual Injuries and Chlorophyll Fluorescence

Planting of olive (Olea europaea L.) tree due to salt and drought tolerance and ever green habit increasingly is considered in urban landscape in recent years. The low resistance to cold has been a major problem in using this tree in temperate and cold zones. So, determination of frost resistance cultivars is one of the important measures for use of this tree in urban landscape. To evaluate frost resistance of 15 olive cultivars and to compare the visual assessment and chlorophyll fluorescence methods, a factorial experiment was carried out using 7- year- old olive trees which were planted in randomized complete block design with 3 replications. In visual method, frost damage of winters 2007 and 2008 to plants (percentage of drying by scoring and percentage of leaf abscission) were measured. Results of this experiment showed that ‘Amphisis’ followed by 'Gorgan' and 'Shengeh' were tolerant and ‘Kroneiki’ and ‘Rashid’ were sensitive cultivars to low temperatures. In method of chlorophyll fluorescence, in July 2008 leave samples of each cultivar was gradually incubated in 0, -5, -10, -15 and -20 ° C for one hour at least. Then Fv/Fm value of each sample was measured with fluorescence spectrometer. Results indicated that 0 and -5 ° C had no damage on samples and all cultivars tolerated these temperatures (Fv/Fm> 0.83). When temperature reduced to -10 and -15 ° C the stress on plants increased and ‘Rashid’ showed the lowest Fv/Fm (0.243 and 0.001 respectively) and was the most frost sensitive. Decreasing temperature to -20 °C had no further significant effect on reduction of Fv/Fm index and showed no difference between cultivars. Based on this method, ‘Shengeh’, ‘Gorgan’ and ‘Amphisis’ were tolerant cultivars and ‘Rashid’, ‘Spain’, ‘Manzanilla’ and ‘Kroneiki’ were sensitive cultivars to low temperatures which confirmed the results of visual assessment.