Study the Responses of Some Plum Rootstock Genotypes to NaCl Salinity Stress

Document Type : Full Paper

Authors

• Maryam Ebadi
• Reza Fatahi
• Zabihollah Zamani
• Ali Ebadi

Department of Horticultural Science, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

Abstract

Keywords

• PPO activity
• Total protein content
• Flavonoids content
• Na+ and K+ content
• Electrolyt leakage

Main Subjects

• Fruit Science

Extended Abstract

Introduction

    The Prunus genus offers a rich genetic diversity that can be used to identify rootstocks being tolerant to salinity. High levels of salinity in water and soil have a detrimental effect on the growth and metabolism of plants, leading to a decrease in yield, particularly in arid and semi-arid regions. Salinity stress has a significant impact on plant growth, as well as on physiological, biochemical and molecular parameters. The majority of stone fruit trees, such as plums, are sensitive to salinity stress and their growth and productivity gradually decrease in soil solutions with salinity concentrations above 1.5 dsm^-1. Due to the limited research reported on Prunus genus and specially plum rootstocks under salt stress, this study aimed to evaluate the physiological, biochemical and antioxidant responses of eight selected rootstock genotypes under NaCl stress.

Materials and Methods

    Eight plum (Prunus cerasifera) genotypes selected for high rooting rate were compared for salt stress (0, 40 and, 80 mM NaCl) tolerance. The plants were cultivated in 12-liter pots and fed with complete fertilizer from the third week of February to late June. The application of salinity stress (0, 40, and 80 mM NaCl) was conducted as a factorial (factors included salinity concentrations and genotype) based on a randomized complete block design for 13 weeks from the beginning of July in the Faculty of Agriculture, University of Tehran, Karaj, Iran. At the end of salinity stress, the shoot and root samples were collected. The measured traits included leaf area, total dry matter (%), chlorophyll fluorescence, total chlorophyll and carotenoids content of leaf, Na⁺ and K⁺ concentrations in shoot and root, K⁺/Na⁺ ratio in shoot, shoot/root Na⁺ ratio, shoot/root K⁺ ratio , electrolytes leakage, total protein, flavonoids of leaf and root and polyphenol oxidase (PPO) activity.

Results and Discussion

    With increasing salinity level, traits such as leaf area, total dry matter (%), chlorophyll fluorescence, total chlorophyll and carotenoids content decreased and other traits including Na⁺ content of shoot, shoot/root K⁺ ratio, electrolyte leakage, and flavonoids content of leaf and root and PPO activity increased. Na⁺ content (shoot/root), K⁺ shoot and total protein content declined in some genotypes and increased in others. Genotypes UTPR2 and UTPR8 retained their leaf area despite increasing salinity levels. The damage of the photosynthetic apparatus was evident with the decrease of the chlorophyll fluorescence, total chlorophyll and carotenoids content, as well as total dry matter (%).The Na⁺ content in shoot increased under salinity sress, and at the highest level of salinity, it was about 1% of dry matter in UTPR5, UTPR6, UTPR7, and UTPR8 genotypes and 1.3-2.7% of dry matter in other genotypes. The K⁺ content of shoot decreased in UTPR1, UTPR2, UTPR3, and UTPR4 genotypes as salinity level increased, while it increased in others, with the significant increase only in UTPR7 genotype. As salinity levels rose, the Na⁺ content (shoot/root) decreased in UTPR5, UTPR6, UTPR7, and UTPR8 genotypes and increased in other genotypes. This could be attributed to the ability of UTPR5, UTPR6, UTPR7, and UTPR8 genotypes to absorb less Na⁺, retain it more in the root, and transfer it less to the shoots. With the increase in salinity, shoot/root K⁺ ratio increased in the genotypes, suggesting that the transfer of K⁺ from the root to the shoots may be a factor in their salinity tolerance. Furthermore, at the highest level of salinity, the electrolyte leakage in UTPR5, UTPR6, UTPR7, and UTPR8 genotypes was lower than other genotypes, which can indicate greater tolerance and less membrane damage of these genotypes. Notably, UTPR5 genotype showed less electrolyte leakage at the highest salinity level. Under salt stress, the total protein content in UTPR1, UTPR2, UTPR3, and UTPR4 genotypes increased, likely due to the accumulation of compatible solutes for osmotic adjustment. The flavonoids content of leaf and root increased more in UTPR5, UTPR6, UTPR7, and UTPR8 genotypes than other genotypes, which could be due to their strong antioxidant systems. In addition, salinity stress increased the PPO activity so that its activity increased more in UTPR5, UTPR6, UTPR7, and UTPR8 genotypes than other genotypes with increasing the salinity.

Conclusion

    At the highest salinity level tested (80 mM NaCl), UTPR5, UTPR6, UTPR7, and UTPR8 genotypes demonstrated greater tolerance to salinity than others due to more total dry matter (%), less Na⁺ content in shoot, more K⁺ content in shoot, less electrolyte leakage and a noteworthy increase in flavonoids content of leaf and root and PPO activity. In this study, Genotypes UTPR1 and UTPR5 were recognized as the most sensitive and tolerant, respectively.