Effectiveness of Seed Priming and Soil Drench with Salicylic Acid on Tomato Growth, Physiological and Biochemical Responses to Severe Water Deficit

This study aimed to assess the capacity of two methods of application of salicylic acid (SA) to mitigate the effects of water deficit during the vegetative growth of tomato (Solanum lycopersicum L.) plants comparatively evaluated by growth, physiological and biochemical responses. Under greenhouse conditions, a combination of two factors was tested. The first was SA application: without SA, seed priming with SA, and soil drench with SA solution at 19 days after seedling emergence. The second factor, water limitation (20, 30, 40, and 100% of water holding capacity of the substrate) was applied 28 days after seedling emergence for 5 days. Results showed that plant growth and photosynthetic activity were significantly inhibited by the water deficit. On the other hand, water use efficiency, activities of superoxide dismutase, ascorbate peroxidase, catalase and contents of malondialdehyde, hydrogen peroxide and osmoprotectants were significantly increased by water deficit. Seed priming with SA induced increases in leaf area, root dry weight and root/shoot ratio under drought conditions. Soil drench with SA induced improvements in CO2 assimilation rate and stomatal conductance in well-irrigated plants. Even when, in general, the activity of antioxidant enzymes was not increased by the application of SA, the cellular redox homeostasis was maintained through increases in the contents of proline and total soluble sugars from the degradation of starch. Seed priming with SA is a suitable technique to mitigate the damaging effects of severe water deficit while maintaining plant growth.