Although extensive work has been reported on winegrapes (Vitis vinifera L.) regarding canopy structure, management and microclimate on berry ripening and composition, scarce information has been devoted to this issue in tablegrapes. Canopy microclimate, photosynthesis and other physiological traits were determined in three year old 'Perlette' vines trained on a T-trellis, in Sonora, Mexico. In the undivided commercial T-trellis UTT) vine canopy, the photosynthetic photon flux densities (PPFD) reaching external, middle and internal leaf layers were 1922, 53 and 34 mu mol m(-2) s(-1), respectively. In the same order, net photosynthesis (Pn) rates were 19.0, 1.7 and 1.0 mu mol CO2 m(-2) s(-1), while chlorophyll contents were 1.9, 1.7 and 1.0 mg mL(-1). No differences in total protein content were found between leaf layers, but significant differences in rubisco specific activity were found among external, middle and internal leaves, reaching 1.07, 0.65 and 0.25 mu mol min(-1) mg(-1), respectively. Four training systems were compared against a commercial undivided T-trellis (UTT): Slanted pergola (Pergola), a specifically designed system (CIAD), Lyre (Lyre) and a divided T-trellis (Divided). Significant differences in PPFD on Lyre, Pergola, CIAD, Divided and UTT yielded 2192, 2076, 1900, 885 and 711 mu mol m(-2) s(-1). At veraison, Pn in Pergola, CIAD, Lyre, Divided and UTT was 12.7, 11, 12.5, 10.5 and 5.1 mu mol CO2 m(-2) s(-1), respectively. Five days after harvest, Pn showed a decrease in all training systems, particularly in UTT which showed only 3.7 mu mol CO2 m(-1) s(-1). Stomatal resistance at veraison and postharvest was highest in UTT with 4.2 and 6.8 s cm(-1) for both periods. Total soluble solids by 27 April were 15.7 degrees Brix for CIAD, while for UTT was only 12.1 degrees Brix. A week later, CIAD, Lyre, Pergola and Divided reported 16.3, 15.9, 15.5 and 15.2 degrees Brix, while UTT reached only 13.1 degrees Brix. Thus by dividing canopies and applying canopy management techniques the harvest date in the early season seedless grapes can be advanced, by increasing light harvest, photosynthetic rate and berry sugar accumulation.
