Genotype × Year Interaction Dominates Mineral Variation in Berry Fractions of Eight Vitis labrusca Cultivars.

The mineral composition of grape berries is shaped simultaneously by genotype and by growing season, yet the relative contribution of each source, and of their interaction, is rarely quantified within a single experimental framework. We determined 13 macro- and micronutrients (N, P, K, Ca, Mg, S, Mn, Fe, Zn, B, Cu, Na, and Cl) in four berry fractions (seed, skin, pulp, and juice) of eight Vitis labrusca cultivars (Concord, Niagara, Steuben, Rizessi, Rizpem, Rizellim, Ülkemiz, and Çeliksu) grown under a uniform, nonirrigated, and non-fertilized regime at a single site over two consecutive growing seasons (2024 and 2025). Data were analyzed within each fraction using a factorial model containing block, year, cultivar, and the year × cultivar interaction, with false-discovery-rate correction applied across all tests. The year × cultivar interaction was significant for 49 of 52 fraction × element combinations and accounted for the largest single share of total variance (mean 39%), exceeding the contributions of cultivar (32%) and year (14%); the interaction was strongest in the pulp (43%) and juice (44%) fractions and reached 74% for pulp manganese. Cultivar effects within a season were significant in 93 of 104 tests. Interannual change was directionally coherent for several elements: all 16 significant changes in iron and all 20 in zinc were increases in 2025, whereas 17 of 19 significant manganese changes and 13 of 14 phosphorus changes were decreases. Cultivars differed substantially in compositional stability between seasons, with Niagara varying least (median 1.75-fold change across elements and fractions) and Concord most (2.87-fold); Niagara and Rizpem were particularly stable in the pulp and juice. Harvest maturity, expressed as soluble solids concentration, was not associated with mineral concentration in any fraction. After cultivar, year, and block effects were removed, 186 of 312 elemental pairs remained significantly correlated, indicating associations that are not merely a reflection of cultivar or seasonal differences. These findings identify genotype × environment interaction, rather than genotype alone, as the principal determinant of mineral variation in V. labrusca berries and suggest that compositional stability is itself a trait that differs among cultivars. Absolute concentrations reported here should be regarded as provisional, because analytical validation data for the present dataset were not available.