Reducing Late Season Berry Dehydration

Summary: Warm, dry conditions can exacerbate late-season berry shrivel, reducing yield and altering berry sensory properties. Late-season shrivel occurs when the berries undergo programmed cell death, and the water released from the ruptured cells is drawn from the fruit to the canopy by a water potential gradient. The goal of our project was to test whether we could reduce shrivel by interrupting these processes. First, 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 programmed cell death, reducing shrivel at harvest. Second, we tested whether blocking the petiole water transport tissue (xylem) would reduce shrinkage by impeding water transport to the canopy. We implemented conventional (following standard commercial practices), early-pulse (before expected onset), and late-pulse (at expected onset) irrigation treatments on mature Cabernet Sauvignon vines in an experimental vineyard at UC Davis. We monitored vine water stress, berry cell death and shrivel, reactive oxygen species concentrations, markers for cell oxidative damage, and berry gene expression. We also used glue to partially block the pedicle for berries in the conventional irrigation treatment and compared diameter shrinkage to undamaged berries. The late irrigation treatment significantly reduced the rate of cell death and the magnitude of berry shrivel at harvest compared to the conventional treatment. However, the early irrigation treatment did not significantly impact cell death or shrivel. Concentrations of the reactive oxygen species H2O2 increased at the same time as cell death, consistent with a role in programmed cell death, but were not significantly different among treatments. We are still analyzing oxidative cell damage and berry transcriptomics, which we expect to provide more insight into the drivers of the treatment differences. Blocking the pedicle xylem did not significantly reduce shrinkage. Overall, these findings show that the time of onset of cell death is not impacted by water stress but using a short pulse of irrigation near the onset of cell death can slow the rate of cell death and reduce berry shrinkage at harvest.