Alleviating Water Stress at Veraison May Trigger Berry Shrivel Disorder in Susceptible Grapevines

<h3>Abstract</h3> <h3>Background and goals</h3> Berry shrivel (BS), a grape ripening disorder which is linked to arrested sugar accumulation and metabolic alterations, is thought to be of physiological origin. Its underlying causes remain unknown, but abrupt environmental changes might be involved. We tested whether BS may be triggered by plant water stress leading up to veraison followed by irrigation with water at different temperatures. <h3>Methods and key findings</h3> In a two-year field trial with deficit-irrigated Cabernet Sauvignon winegrapes in arid southeastern Washington, irrigation was suspended during the lag phase of berry development, then resumed at veraison, using either water at ambient temperature (20 to 24°C) or ice-cooled water (0°C). Measurements of soil moisture, leaf water potential, and leaf gas exchange showed that interrupting irrigation induced moderate-to-severe plant water stress before rewatering. Compared with ambient-temperature water, cooling the irrigation water used for rewatering reduced the soil temperature by 4 to 8°C for 1 to 3 days, but had a minor effect on the vines’ response to water stress. Rewatering at 50% veraison, but not at 5% veraison, significantly increased BS incidence. Cooling the irrigation water also tended to increase BS incidence, but not consistently so. <h3>Conclusions and significance</h3> This study showed that sudden alterations in plant water availability and water temperature may be involved in triggering BS. Though the cause-effect relationship remains unclear, this knowledge may be useful in devising vineyard irrigation or soil management strategies that avoid abrupt changes in soil moisture and soil temperature around veraison.