Enhancement of Growth and Fruit Maturity in 2-year-old Grapevines cv. Delaware by 5-Aminolevulinic Acid

The influence of 5-aminolevulinic acid (ALA) on the growth, photosynthesis, and fruit quality of gibberellin-induced seedless 2-year-old “Delaware“ grapevine was examined. The result of soil treatment (0.1–10 mg l⁻¹) and foliar spray treatment (30–300 mg l⁻¹) with ALA after flowering was significant growth improvement, up to 55% in the lateral shoot, and up to 38% in leaf area. Optimal doses were 1 mg l⁻¹ soil treatment and 100 mg l⁻¹ foliar treatment. The photosynthetic rate of plants treated with ALA increased by a significant 9.2%–22.5%. Relative to the control, based on measurements of the 5th leaf of each shoot in the ripening period, the optimum concentrations for growth and photosynthesis enhancement in grapevines were 100 mg l⁻¹ (foliar treatment) and 1 mg l⁻¹ (soil treatment). Total plant weight at harvest increased a significant 13% at the optimal treatment doses. In terms of fruit quality, the cluster fresh weight increased a significant 44.9%–53% and fruit colour showed a tendency to become darker in all plants treated with ALA. The °Brix value in the plant treated with 100 mg l⁻¹ ALA was a significant 2.7% higher than that of the control. We consider that leaf area and photosynthetic rates during cultivation are important for the acquisition of photoassimilates and that these are likely to be causally associated with improvement of total dry weight and advance of fruit quality. In addition, a possibility of advancing the harvest time of grapes by ALA treatment was shown.