Morpho-physiological alterations and resistance to Tetranychus urticae in strawberries plants treated with salicylic acid

This study aimed to assess the effect of different concentrations of exogenous application of salicylic acid (SA) (0, 20, 40, 60, and 80 mg L−1) on the density of trichomes, the fluorescence, and resistance to two-spotted spider mite (Tetranychus urticae) in strawberry leaves. The Sweet Charlie and Aromas strawberries cultivars were used in a greenhouse. Seven days before flowering, strawberries were infected artificially with mites. Foliar spraying with SA began when the plants started blooming. The trichome density and the types of leaf trichomes on the abaxial and adaxial leaf surfaces were assessed. The number of live deposited eggs and adult mites present on the abaxial face of each leaf was counted. Additionally, the fluorescence parameters were estimated (initial, maximum, and variable fluorescence, and the effective quantum yield of the photosystem II). SA concentration positively influenced the trichomes density. The number of adults and eggs of mite showed a positive effect when applied in moderate doses in both tested cultivars. Similarly, in the fluorescence analysis, the photosynthetic apparatus suffered a stress reduction, when moderate concentrations of SA were applied. The highest concentration (80 mg L−1) and the control group resulted in the highest energy losses during the redox reactions of the electron transport chain and minor resistance against the mite. Results indicated that SA in concentrations intermediaries (40 to 60 mg L−1) efficiently promotes plant defense responses in strawberries to stress by two-spotted spider mites, through morphoanatomical changes in leaves and better protection of the photosynthetic apparatus.