Abstract
BACKGROUND: Root-applied low-concentration NaCl (e.g., 40 mM) has been shown to maintain the yield and enhance both nutritional and functional quality in salt-sensitive strawberry cultivars. However, the potential benefits of foliar low-concentration NaCl application on strawberry plants have rarely been investigated to avoid secondary soil salinization through long-term root application, especially the effects on fruit quality during greenhouse high-temperature periods. METHODS: Strawberry (Fragaria × ananassa Duch. cv. Benihoppe) plants were foliar sprayed with 0 (CK), 5, 10, 15, and 20 mM NaCl solutions once a day from fruit setting to ripening under high-temperature period in a solar greenhouse where quality deterioration was observed. The physiological traits of strawberry leaves and the quality of fruits were measured to explore the beneficial effects of low-concentration NaCl solutions. RESULTS: Compared with the control (CK), foliar spraying with low-concentration NaCl solutions significantly increased the photosynthetic efficiency and mineral element content of strawberry leaves; enhanced the color of strawberry fruits; and increased the weight, size, color, soluble sugar content (e.g., glucose, fructose, and sucrose), and secondary metabolite production (e.g., vitamin C, phenolics, and flavonoids) of strawberry fruits. Additionally, foliar spraying with low-concentration NaCl solutions significantly decreased the organic acid content (e.g., malic and citric acids) in strawberry fruits. According to redundancy analysis, foliar spraying with NaCl induced the accumulation of Na in strawberry leaves and Cl in strawberry fruits, which may have contributed to the increase in physiological activity of leaves and the improvement in fruit quality, respectively. CONCLUSION: The foliar spraying of 10-15 mM NaCl, an economical and beneficial method, improves photosynthetic efficiency, thereby promoting formation and accumulation of strawberry fruit nutrients under high-temperature period in greenhouses.