The challenge of improving oenological quality in favorable conditions for productivity

Abstract

Context and purpose of the study – Marselan (Cabernet-Sauvignon x Grenache), has been planted for more than 20 years now in Uruguay. Due to its good agronomic and oenological aptitudes under uruguayan conditions, it is currently the red variety with highest plantation rate. The objective of the study was to identify management practices, aimed at improving quality in highly productive vineyards, different fruit/leaf regulation methods were tested in southern Uruguay.

Material and methods – The experiment was carried out during 2020 and 2021 seasons, on a non-irrigated Marselan/110R vineyard, planted in 2002 in Lyra (3.0 x 1.25 m – row x plant spacing) in the Cerrillos region, Canelones, Southern Uruguay. Plants were pruned to double guyot (28 buds per plant). The interrow was maintained with permanent cover crops. Five treatments were applied in a complete randomized block design, with three repetitions. Pre-flowering defoliation (PFD) at stage 17 (Coombe, 1995), defoliation at fruit set (DC) at stage 29 (Combe, 1995), the same treatments in combination with cluster thinning at veraison (PFD+R and DC+R) and an untreated control (T). Plots comprised 10 consecutive plants.

Results – Control treatment was associated with higher yield, Ravaz index and lower soluble solids and anthocyanins concentration (Table 1 y 2). Related to a lower bunch exposure (PAR % at fruit zone) bunch rot incidence was also significantly higher than in defoliation treatments (Table 1). Total leaf area was not significantly affected by DC or PFD treatment. Leaf area in PFD treatment, was recomposed from the greater development of lateral shoots from basal buds. As a result, PAR % at the fruit zone was significantly higher in DC compared to PFD. PFD treatment significantly reduce fruit yields the first season, however yield was comparable with the treatments without cluster thinning the second season. The high number of clusters in PFD treatment the second season compared to T and DC (no cluster thinning treatments) suggest an improved conditions for cluster induction. Probably the reduction of crop early in season may also affect the reserves accumulation. Although PFD+R and DC-R increased the leaf/fruit ratio, mostly explained by cluster thinning (R), total vegetative growth (pruning weight) was also increased. In terms of grape composition, defoliation treatments in combination with crop adjustment, produced berries with higher concentration of all secondary metabolites associated with oenological quality. The impact of PFD and DC on fruit composition and wine anthocyanins concentration was minor compared to it observed associated to cluster thinning (R).  PFD treatment significantly reduce cluster compactness and bunch rot. This is undoubtedly a relevant effect for humid climate viticulture. In our experiment all treatments were harvested at the same day, however the opportunity to reach fruit full maturation even under favorable conditions for bunch rot development, may be considered the main advantage of this practice compared to a later leaf removal (DC).