Non-Invasive Assessment of Grape Berry Development and Metabolic Maturation Under Tropical Field Conditions

Non-destructive monitoring of fruit ripening is essential for optimising harvest time, yet its application to tropical viticulture remains largely unexplored. This study evaluated in situ chlorophyll a fluorescence as a non-invasive physiological marker to track berry development and metabolic maturation in two table grape cultivars (Vitis labrusca L. var. Niagara Rosada and var. Romana) under tropical field conditions, characterised by the latitude position, absence of chilling-induced dormancy, and variable rainfall during ripening. Berries’ fluorescence parameters (Fo, Fm, Fv and Fv/Fm) were monitored weekly from the pea-size stage to commercial harvest (67–123 days after pruning) using a portable modulated fluorometer, along with chlorophyll and quality trait measurements. A decline in fluorescence parameters during maturation coincided with chlorophyll degradation and the accumulation of glucose and fructose. The maximum quantum yield of PSII (Fv/Fm) remained stable (≈0.75) throughout development, indicating sustained photochemical efficiency despite chloroplast disassembly. Significant correlations (r > 0.80) were established between fluorescence parameters and key maturity indices, with distinct cultivar-specific patterns evident between the NR and RM cultivars. Therefore, chlorophyll a fluorescence provided a reliable, portable, non-destructive tool for monitoring ripening dynamics and estimating quality parameters in table grapes, offering practical advantages for tropical viticulture where environmental variability demands flexible monitoring.