Foldable lyre impacted the agronomic performance and phenolic profiles of ‘Merlot’ grapes cultivated in a humid temperate climate

Abstract

The training system plays a key role in viticulture, influencing canopy structure, yield, grape and wine composition. This study evaluated the impact of vertical shoot positioning-VSP and foldable lyre training systems set at 20°, 30°, and 40° angles, on the production and biochemical profiles of ‘Merlot’ grapes at Serra Gaúcha, southern Brazil. The experiment was conducted in an experimental vineyard planted in 2018, using cv. Merlot clone 181 grafted onto ‘Paulsen 1103’ rootstock, spaced 3.2 m between rows and 1.5 m between plants, trained in a double spur-pruned cordon system. A randomised complete block design was adopted, evaluating four training systems and two consecutive seasons. The variables analysed included number of shoots and bunches, percentage of budburst and production per vine, leaf area, leaf area-to-production ratio, accumulated photosynthetic photon flux density in the bunch zone, pH, soluble solids, titratable acidity, and phenolic composition of grapes determined by UPLC/MS. In general, the foldable lyre system increased vine leaf area, and production up to 50% as compared to Vertical Shoot Positioning-VSP, without significant changes in pH, soluble solids, or titratable acidity. Shoot and bunch number, sunlight exposure, and phenolic content were impacted, increasing the amounts of some anthocyanins, flavonols, flavononols, stilbenes, and flavanols and procyanidins on grapes. Overall, the foldable lyre system outperformed VSP, enhancing production and some important phenolic composition in grapes. PCA applied on phenolic compound data showed that vintage was the main factor influencing grape composition, as compared to training system. But when phenolic profiles were evaluated in individual vintages, grapes were strongly impacted by training system, showing different profiles. Therefore, foldable lyre system can be recommended as alternative for ‘Merlot’ grape production in the Serra Gaúcha region, thinking in a sustainable viticulture.