Girdling, gibberellic acid and forchlofenuron: effects on yield, quality and metabolic profile of table grape cv Italia

Among the various vineyard treatments adopted in recent years for table-grape cultivation, there has been a significant use of plant growth regulators (PGRs) and girdling to increase berry size and yield. In particular, an increase in the application of forchlorfenuron (CPPU) and gibberellic acid (GA3) for many seeded and seedless table-grape cultivars has been registered in several countries. In this two-year study, girdling at berry set, gibberellic acid (10 mg/L) applied at berry diameter of 10 to 11 mm, and forchlorfenuron (9.75 mg/L) applied at berry diameter of 11 to 12 mm were investigated to verify their effects on berry size, yield, and chemical and metabolic characteristics of Italia grapes. In general, at harvest all treatments significantly increased berry diameter, length, and weight and consequent cluster weight and yield/vine compared to an untreated control. The treatments showed significant differences for the colorimetric parameters, in particular a higher value of hue for berries treated with GA3 and CPPU, thus shifting the skin color from yellow toward yellow-green. Metabolomic study carried out by nuclear magnetic resonance spectroscopy combined with principal component analysis indicated that metabolic profile depends on the year and, in each year, the effect of treatments consisted of a slight variation of amino acid content. Treatments effects were more pronounced in the year characterized by a cooler summer.