Irrigation Timing Affects Grape Berry Cell Death and Late-Season Dehydration

<h3>Abstract</h3> <h3>Background and goals</h3> Hot, dry conditions can exacerbate late-season berry dehydration, reducing yield and wine quality. Late-season dehydration occurs as mesocarp cells die, releasing water that is lost to berry transpiration or backflow to the canopy. We tested whether short pulses of increased irrigation could reduce late-season berry dehydration by interrupting stress-induced signals for cell death. <h3>Methods and key findings</h3> Conventional irrigation was compared with an early- and a late-pulse treatment, where irrigation was increased by ~40% in the 2 wk immediately before or after the expected onset of cell death (~90 days after anthesis). We imposed each treatment on five vines of Cabernet Sauvignon growing in an experimental vineyard in Davis, California in an atypically hot (2022) and cool (2023) growing season. We monitored vine water potentials, berry cell death and shrivel index, and concentrations of putative signals for cell death (i.e., hydrogen peroxide [H₂O₂]) and markers of cellular damage. The late-pulse treatment significantly reduced the rate of cell death and the magnitude of berry shrivel at harvest, but only in the hot season (<i>p</i> &lt; 0.05). Conversely, the early-pulse treatment did not affect the rate or timing of onset for cell death or shrivel (<i>p</i> &gt; 0.05). H₂O₂ levels increased with cell death but were not affected by irrigation, indicating that other mechanisms produced the treatment effects on cell death. <h3>Conclusions and significance</h3> These findings suggest the onset of cell death is robust to irrigation, but a short pulse of supplemental irrigation soon after onset can slow the rate of cell death and mitigate late-season berry dehydration under hot growing conditions.