Investigation of Drought Tolerance Using Metabolites and Photosynthetic Characters in Zard Olive (Olea Europaea L.) Cultivar Plants

Olive has been well adapted to arid and semi-arid climates due to leaf structure and drought tolerance mechanisms. Zard is a native double-purpose cultivar and the most important olive cultivar in Iran. This study was conducted to investigate the effect of drought stress on some metabolic, morphological and physiological traits of Zard cultivar plants under greenhouse conditions. One-year old plants (self-rooted) of Zard cultivar were used in this study. Self-rooted plants were transferred to 10 kg pots containing 1:1:1 sand, field soil and cocopeat and kept for six months with optimal irrigation and nutrition conditions. By considering the field capacity as control treatment, three treatments of 75, 50 and 25% of field capacity were defined as drought stress (totally four treatments) and the experiment was continued for 60 days. The experimental design was a completely randomized design with four drought stress treatments in three replications and two plants per replicate. Results showed that the moderate and severe drought stress significantly reduced stomatal conductance and transpiration and consequently reduced the differences between the leaf and air temperatures. Despite of decrease in photosynthesis rate, its difference was significant in stresses greater than 0.5FC, indicating that the drought tolerance mechanisms were activated in this cultivar. Reduced photosynthesis rate was due to reduction in chlorophyll content per unit leaf area and also in carbon dioxide assimilation and consequently reduction in stomatal conductance. Increased accumulation of proline and total phenol caused to boost the plant tolerance to drought stress. Based on the responses of olive plants to drought stress, it was concluded that Zard cultivar was tolerant to drought stress up to 0.5FC level. According to growth indices, Zard olive cultivar can be recommended for orchards in regions with scarcity or marginal water conditions. Results showed that moderate and severe drought stress significantly reduced stomatal conductance and transpiration from leaf surface and consequently leaf Δtemperature. Despite of decrease in photosynthesis rate, its differences were significant in stresses greater than 0.5FC, and indicating that drought tolerance mechanisms were activated in this cultivar. Reduced photosynthesis rate was due to the decrease in chlorophyll content per unit leaf area altogether with decrease in carbon dioxide assimilation because of decrease in stomatal conductance. Increased accumulation of proline and total phenol cause to boost the plant tolerance to drought stress. Based on the reactions of olive plants to drought stress, it was concluded that Zard cultivar was tolerant to drought stress up to 0.5FC level. According to growth indices, Zard olive cultivar can be recommended for orchards of regions with scarcity or marginal water conditions.