The elimination of a certain number of leaves around bunches at veraison is a common practice applied in vineyards to improve cluster microclimate, reduce grape rot and positively affect grape ripening and in particular anthocyanin and flavonol composition.
In the present research, we analyze the effect over two years of veraison leaf removal on grape ripening in four red varieties Cabernet Sauvignon, Nero d’Avola, Raboso Piave and Sangiovese, grown in the same agronomical conditions and characterized by different anthocyanin and flavonol profiles.
The control berries temperature overcome 30°C for several hours during the two seasons and increased in defoliated berries. In both vintages, veraison defoliation did not affect yield parameters, sugars and anthocyanins concentrations, slightly reduced bunch rot but strongly increased flavonols concentrations.
Veraison defoliation affected anthocyanin composition leading to an increase of the di-substituted (cyanidin and peonidin) to tri-substituted (delphinidin, petunidin and malvidin) anthocyanin ratio in Nero d’Avola, Sangiovese and partially in Raboso Piave, while in Cabernet Sauvignon showed a contradictory behaviour. Flavonol composition varied following defoliation in all the varieties, mainly driven by quercetin increase, reducing the original flavonol profile differences among varieties.
The practical implications of this research showed that veraison defoliation may induce a specific response at the split-up point of the biosynthesis of di- and tri-substituted flavonoids, in varieties characterized by different flavonol profile and by low (Cabernet Sauvignon, Nero d’Avola) or high (Sangiovese and Raboso Piave) di/tri anthocyanin ratio with possible inferences in the grape enological features.
Article based on the poster presented at the at the 10th edition of Enoforum (May 16th-18th, 2017, Vicenza, Italy)