Leveraging Berry Physiology To Mitigate Late-Season Dehydration. AVF Project #2024-2739.

Summary of Progress:

Hot, dry conditions can exacerbate late-season berry dehydration, reducing yield and altering berry sensory properties.  Late-season dehydration occurs when the berries undergo programmed cell death, and the water released from the ruptured cells is lost to transpiration or backflow to the canopy.  Climate change is expected to make many wine regions warmer and drier, exacerbating these issues.  Thus, the goal of this project is to identify management strategies to reduce late-season dehydration and its effects on yield and quality.  In Year 1 and 2, we tested whether short (2-week) pulses of increased irrigation before or at the expected onset of cell death would reduce water stress-induced oxidative damage and delay or reduce the rate of cell death, reducing shrivel at harvest.  We found that the irrigation pulse at onset significantly reduced the rate of cell death and berry shrivel at harvest, providing irrigation guidelines to reduce late-season dehydration.  This year, we tested (1) whether evaporative cooling (misting) systems would reduce cell death and shrivel with less water than the irrigation pulse and (2) used a rootstock/Cabernet Sauvignon clonal trial to screen for plant material with less susceptibility to these processes.  Misting systems significantly reduced cluster temperatures and vine water stress (p<0.05) and, on average, increased berry weight and TA and reduced TSS and pH, though these differences were not significant (p>0.05).  Vine gas exchange and water stress, yield, and berry mass and composition also varied significantly across rootstocks and clones (p<0.05).  However, unexpectedly, we did not find significant cell death in any treatment or rootstock/scion combination in >130 images.  Extensive troubleshooting did not identify a problem with the imaging method; instead, extreme pre-veraison heatwaves could have reduced berry size, making it easier for oxygen to permeate the entire berry, which has been hypothesized to reduce cell death.  This year, we will repeat this work and include additional experiments and troubleshooting to test the hypothesis that heat during fruit set reduces cell death and shrivel, contrary to heat after veraison, or resolve any imaging issues to test the effects of misting and plant material on these processes.