Effect of Salinity on Growth and Physiological Parameters of Four Olive (OleaeuropaeaL.) Cultivars underGreenhouse Conditions

Salinity is a common abiotic stress that seriously affects crop production around the world, particularly in arid and semi-arid regions.The deleterious effects of salinity on plant growth are associated with low osmotic potential of soil solution (water stress), nutritional imbalance, specific ion effect (salt stress), or a combination of these factors. Olive is one of the most important fruit crops in Iran and the world. Despite olive has been classified as moderately salt tolerant plant, poor quality of irrigation water in association with salt build-up soils has reduced the yields, especially in arid and semi-arid regions of Iran. The tolerance of the olive to salt is to a great extent depends on the cultivar. Selecting salinity-resistant cultivars is one of the most important strategies used for mitigating salinity effects on olive. Therefore, this study was performed to assess the salt tolerance of four olive cultivars under greenhouse condition.
For this purpose, one-year-old rooted cuttings of Iranian olive cultivars (‘Dakal’, ‘Shiraz’, ‘Zard’) and non-Iranian cultivar ‘Amigdal’ were grown in the research greenhouse of Agricultural College, Isfahan University of Technology of Iran. Plants were grown in plastic pots. The pots were 180 mm in diameter and 20 mm in depth with volume of 7 L. The minimum and maximum temperatures during the experiment period were 19 and 35˚C, respectively. After sticking the cuttings, the pots with uniform plants were subjected to the treatment with 0 (control), 100, 150 or 200 mMNaCl. The electrical conductivities of these solutions were 0.003, 10.52, 15.43 and 19.55 dS m-1, respectively. To avoid osmotic shock, the NaCl concentration was gradually increased. The layout was a 4×4 factorial experiment based oncompletely randomized design, with four replications. The experimental measurements were carried out three months after beginning the salt treatments.
The results showed that salt stress and cultivar hadsignificant effects on all of vegetative and physiological parameters. Injury rating valueof plants wasfound to increase significantly as the salt concentration was raised. Among the cultivars, the highest injury rating value (2.75) belonged to Amigdal cultivar, while the lowest means (2.00) was related to Dakal cultivar. By increasing the salinity level, stem heightincreasing ratesignificantly decreased. The lowest means (18.17%) belonged to 200 mMNaCl treatment, showing 81.83% decrease compared with control. Among the cultivars, Zard showed the highest means of increase in stem height (71.75%). Leaf area influenced significantly by salinity, sothat the lowest means of leaf area (35.05%) was recorded for200 mMNaCl treatment, showing a 69.91% decrease compared with the control. The highest leaf area belonged to Shiraz cultivar, which had a significant difference with Zard and Amigdal cultivars. Compared with the control, salinity caused 50.83% and 54.36% decreases in shoot fresh and dry weight in 200 mMNaCl, respectively. The highest shoot fresh and dry weightswere recorded forZard cultivar. The lowest shoot fresh and dry weights were observed forAmigdal cultivar.Increment of salinity concentration significantly declined root fresh and dry weight. Among the cultivars, the highest means of root fresh weightbelonged to Amigdal cultivar, whereas the lowest was related to Shiraz cultivar. The highest and lowest root dry weightswere observed forDakal and Amigdal cultivars, respectively.Salinity significantly decreased relative water content.The lowest leaf relative water content (66.04%) was recorded in 200 mMNaCl treatment, showing a 23.43% decrease compared with the control.Zard cultivar showed the highestleafrelative water content. Salinity stress decreased chlorophyll fluorescence in leaves of salt-treated olive plants. At 200 mMNaCl, leaf chlorophyll fluorescence was minimal as compared to control and other salt levels. The highest leaf chlorophyll fluorescence ratio (0.74) was recorded forZard cultivar. However, Amigdal cultivar showed the lowest means for this index (0.60).Salinity significantly decreasedleaf chlorophyll content.The lowest leaf chlorophyll content (69.39%) was recorded in 200 mMNaCl, showing a 66.80% decrease compared with the control.Among the cultivars, Zard showed the highest leaf chlorophyll content (170.33). In the present study, the increase in proline content in the NaCl-treated plants was noted, with the highest level being attained with 200 mMNaCl. The highest proline content (1.03 µmol.g-1 F.W.)was observed in Zard cultivar. Salinity stress increased malondialdehyde content in the leaves of salt-treated plants. The highest malondialdehyde content was obtained from leaves of plants treated with 200 mMNaCl. The highest malondialdehyde content was recorded in Amigdal cultivar.Shirazl cultivar showed the lowest malondialdehyde content. In this study, the correlation betweenvegetative and physiological parameters of olive plants subjected to salt stress was analysed. These correlations suggested that salt injury symptoms was negatively correlated with relative water content, leaf chlorophyll fluorescence and leaf chlorophyll content, but positively correlated with proline content and malondialdehyde content.
In overall, this investigation revealed that salt stress had aninhibitory effect on the vegetative growth of olive plants.The responses of olive cultivars to salt stress suggested that Zard and Shiraz cultivars were more tolerant and ‘Amygdal’ was the most sensitive to changes in the salt levels.