Inductions of Defense Response in Olive Plants against Verticillium dahliae through Application of Salicylic Acid as Abiotic Inducer

Aims: To find suitable approach to control V. dahliae, we evaluated the potential of salicylic acid in the induction of systemic resistance in olive plants and determine whether acquired resistance is correlated with soluble proteins and polyphenol contents.

Place and Duration of Study: This work was performed in the Laboratory of Phytopathology at the Olive Tree Institute (Sfax, Tunisia) between July 2014 and June 2015.

Methodology: Olive plants were pre-treated with 10 mM salicylic acid and then inoculated with pathogenic V. dahliae isolate. Symptoms were monitored for three months and plant tissues samples were regularly analyzed for their soluble protein and polyphenol contents at 15, 30 and 45 days after inoculation. The effect of salicylic acid treatment on soluble proteins expression was evaluated using SDS-PAGE.

Results: Pre-treatment with salicylic acid resulting in a decrease of disease incidence from 91.96% to 29.33% after 45 days of pathogen inoculation. The maximum increase in soluble proteins content was recorded in salicylic acid pre-treated plants with 1.5-fold, 1.87-fold and 2.25-fold at 15, 30 and 45 days after pathogen inoculation as compared to control plants. Similarly, phenol content was also significantly higher in salicylic acid treated plants, representing 1.5-fold, 2.1-fold and 2.7-fold at 15, 30 and 45 days of inoculation as compared to the control plants. Correlation coefficient analyses revealed that there was negative correlation between disease severity, soluble protein and polyphenol contents after 15, 30 and 45 days of treatment. Protein profiling by SDS-PAGE revealed that salicylic acid induced the synthesis of new proteins. The genomic DNA integrity was confirmed by obtaining of unique RAPD banding patterns for treated and untreated plants.

Conclusion: Overall, a pre-treatment of olive plants by salicylic acid lead to low disease severity and suppress the fungus pathogenicity through overexpression of proteins and polyphenol compounds involved in plant defense.