Abstract
Drought is important abiotic stress that negatively influences the growth and development of plants. Strong efforts are currently ongoing worldwide to improve olive production under adverse environmental conditions by extending genetic diversity to improve key agro-physiological and biochemical features through various breeding programs. This research was performed to evaluate the effect of drought stress on the changes of some physiological and biochemical traits in 20 commercial and promising olive genotypes under field conditions during 2015-2017. Fruit oil content as well as some of physiological traits and antioxidant activities under control and drought stress conditions were evaluated. The results of combined analysis of variance (ANOVA) for fruit yield and other measured traits showed that year, irrigation treatments, genotype main effects and their interactions were highly significant. In general, fruit yield, relative water content (RWC), oil content and total soluble proteins (TPs) showed a decreasing trend, whereas the electrolyte leakage, H2O2 content and activity of catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POX) displayed an increasing trend in the tested olive genotypes during drought stress. A Principal component analysis (PCA)-based biplot demonstrated that stress tolerance index (STI) positively correlated with POX and TPs. Results also revealed a high level of genetic diversity in the tested olive genotypes, and among them, two commercial (Abou-satl) and promising genotypes (T2) responded better to drought by marinating a good balance for fruit yield and some of the antioxidant activities. These genotypes could be used in future programs to develop new olive cultivars with beneficial stress-adaptive traits.
Highlights
Olive (Olea europaea) is an evergreen tree and it had been known as one of the oldest cultivated species in the world
Plant cells respond to drought by inducing scavenging of reactive oxygen species (ROS) and activating antioxidant defence compounds (30, 31)
Some of the measured traits such as relative water content (RWC), total soluble proteins (TPs), FY and DFO decreased by varying degrees
Summary
Olive (Olea europaea) is an evergreen tree and it had been known as one of the oldest cultivated species in the world. The olive tree is known for its tolerance to prolonged drought periods (1). Growth of olive tree is affected by drought stress through a change in anatomical, morpho-physiological and biochemical mechanisms. Many morpho-physiological and biochemical traits have been found to be associated with drought tolerance through higher water potential gradient between root system and canopy (6), development of osmotic adjustment (7), limitation of water loss through modulation of stomatal closure (8), decrease of leaf area and increase of stomatal density (9). It has been shown the tolerant olive cultivars revealed lower stem growth (10), smaller leaf area and lower stomatal conductance (9), lower leaf water content (11) under drought condition than optimal conditions. Response to drought stress is different among olive cultivars (11)
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