https://doi.org/10.37229/fsa.fjb.2026.04.19

A two-season field experiment was conducted during 2023 and 2024 on eight-year-old Flame Seedless grapevines grown on sandy soil in a private orchard located west of the Western Desert Road, Minia Governorate, Egypt, to investigate the effect of foliar application of a mixture of amino acids — tryptophan, methionine, and cystine — at graded concentrations (0.05, 0.1, and 0.2%) applied once, twice, or thrice per season on vine yield components, cluster physical characteristics, berry physical properties, and berry chemical quality. The experiment was arranged in a randomized complete block design (RCBD) with ten treatments and three replicates. Results demonstrated that all amino acid treatments significantly increased berry setting percentage, yield per vine, cluster weight, cluster length, and cluster shoulder in both seasons; cluster number per vine was unaffected in the first season but significantly increased in the second season, reflecting a cumulative vine conditioning effect. Berry shot percentage was significantly reduced, while berry fresh weight, longitudinal diameter, and equatorial diameter were significantly increased by all treatments. Berry TSS%, TSS/acidity ratio, total anthocyanin content, and reducing sugar percentage were all significantly elevated, while total acidity was significantly reduced. The highest values for virtually all parameters were recorded with AA at 0.2% applied thrice, which was frequently statistically comparable to AA at 0.1% applied thrice. It is concluded that three foliar applications of the amino acid mixture (tryptophan, methionine, and cystine) at 0.1% — at the onset of vegetative growth, immediately after berry set, and one month thereafter — represent the most economically favorable treatment for improving vine yield, and berry quality of Flame Seedless grapevines grown under the sandy soil conditions of Minia Governorate.