UC Davis

Late season dehydration (LSD) is a type of berry shrivel in wine grapes occurring at the end of ripening as a result of cell death in the mesocarp of mature berries and is accelerated by late season water deficits. Increasing temperatures and erratic precipitation are projected for California’s winegrowing regions this century, rendering grapevines more vulnerable to late season dehydration and consequently growers to yield losses. This study sought to investigate whether augmented volumes (‘pulses’) of irrigation prior to (the early treatment) or during (the late treatment) the onset of cell death would effectively postpone it. Water potential and gas exchange measurements were compared to mesocarp cell death, degree of berry shrivel, and chemical agents and products of cell death. Our study found that a 40% difference in irrigation volume for our pulses did not effect changes in water potential, stomatal conductance, or photosynthesis, however the late treatment significantly slowed the rate of cell death and yielded more turgid berries at harvest. Other aspects of berry quality, at harvest, (°Brix, TA, pH) did not respond to our treatments. We observed a spike in H2O2 at the onset of cell death and found significant correlation between tissue vitality and H2O2 concentrations throughout the experimental period. Thus, our study confirmed the relationship between H2O2 accumulation and berry shrivel, and found a potential irrigation strategy for mitigating LSD-related yield losses. A complete picture of the mechanism of LSD is needed to fully explain how shrivel responds to irrigation: future studies on this topic could provide an account of water dynamics in the berry in relation to cell death and irrigation by additionally monitoring hydraulic conductivity in the pedicel. Further investigation into transcriptional changes before and during the onset of cell death will also be needed to determine the contribution of programmed cell death late in berry development.