Vegetative growth, mineral change, and fruit quality of ‘Fuji’ tree as affected by foliar seawater application

• Foliar seawater spray led to increased SSC level and SPS, SS, and neutral invertase activities.
• Seawater treatment resulted in significant increase in anthocyanin levels.
• An increase in K+/Ca2+ but decreases in Ca2+ and K+ levels were observed in fruit.
• Seawater treatment did not affect the vegetative growth and levels of chlorophyll, N, Na+, K+, and Mg2+ in leaves.

Extensive researches have been conducted over the decades to investigate the effects of seawater on many crop plants either by irrigation or foliar spray in an attempt to enhance the yield and quality. The purpose of this study was to quantitatively determine the effects of different foliar seawater sprays on vegetative growth, fruit quality and yield of eight-year-old ‘Fuji’/M.9 apple trees. A field experiment was conducted using two different concentrations of seawater (100 or 50-fold dilution) starting from 130 DAFB (days after full bloom) at 5-day intervals between the treatments. Foliar seawater sprays to ‘Fuji’ tree led to increased levels of fruit soluble solids along with higher activities of sucrose phosphate synthase (SPS) (EC 2.4.1.14), sucrose synthase (SS) (EC 2.4.1.13) and neutral invertase (EC 3.2.1.26). In addition, a significant increase in anthocyanin concentration was observed, especially when ‘Fuji’ trees were sprayed three times with 50-fold diluted seawater. Foliar seawater sprays also resulted in increases in Na+ concentration and K+/Ca2+ ratio in fruit. In contrast to fruit, the levels of N, Na+, K+, Mg2+ in leaves remained unchanged regardless of different seawater treatments. Moreover, foliar seawater sprays did not affect the vegetative growth since leaf area, leaf fresh weight, shoot elongation, and chlorophyll content did not differ significantly from those of control plants. The results suggest that foliar seawater treatments could be useful for improving fruit quality without affecting the yield.