The relationships between the water status of the vine, berry firmness, cracking and sour rot

Berry cracking is one of the major problems that face grapevine production because it commonly leads to sour rot. Cracking is believed to be partially related to the plant water status, though direct evidence for this assumption is lacking. We hypothesized that deficit irrigation would reduce the berry firmness, leading to lower cracking and sour rot incidence. The research was conducted over three seasons (2023–2025) on 'Scarlotta Seedless' vines using four irrigation regimes that tested the effect of the irrigation dosage and timing on sour rot incidence. We followed the plant water status, berry weight, firmness and sour rot incidence. The low water treatments had lower stem water potential (Ψ stem ), berry size, firmness, and lower incidence of sour rot in a season-dependent manner. Water deficit only at pre-veraison or post-veraison stages were less effective in mitigating the cracking incidence compared with sustained water deficit. Positive correlation was obtained between Ψ stem and firmness, and the correlation was even stronger when the seasonal integral of Ψ stem was used, highlighting the instantaneous water balance is less critical in shaping firmness compared with the effect of the irrigation on berry development. Healthy clusters incidence was negatively correlated to firmness with a value of 2.47 N corresponding to 80% healthy clusters. Our findings highlight, for the first time, the link between irrigation, firmness and sour rot, presumably mediated through cracking. Deficit irrigation could be a sustainable mitigation strategy for cracking and sour rot, though this should be further investigated on more cultivars and environments.