Stem Water Potential Is a Sensitive Indicator of Sweet Cherry Fruit Growth and Quality during Near-harvest Irrigation Withholding

The effects of near-harvest irrigation on sweet cherry (Prunus avium L.) fruit quality are not clear. Deficit irrigation during the final stage of fruit growth has been associated with a loss of fruit size. On the other hand, producers have observed fruit softening from irrigation events applied too close to harvest. We evaluated the effects of withholding irrigation for varying pre-harvest durations on sweet cherry yield, fruit growth, stem water potential, gas exchange, fruit quality and cracking susceptibility. In 2014 and 2015, irrigations were withheld from nine and ten-year-old ‘Skeena’ or ‘Sweetheart’ trees for 15, 10, or 5 days prior to harvest and compared to well-watered controls. In both years, yields were unaffected by withholding irrigation treatments, irrespective of the duration or cultivar. Fruit growth was reduced by withholding irrigation for 10 or 15 days prior to harvest, but only when stem water potential reached values ≤ -1.5 MPa around 5 days from harvest. Small fruit size was associated with lower relative water content but not reduced dry matter. Photosynthesis rate was unaffected by withholding treatments so long as stem water potential remained above -1.5 MPa. Fruit firmness was reduced but not significantly when irrigation was withheld for 10 or 15 days. Skin color, soluble solids concentration and titratable acidity remained unaltered by withholding treatments. Fruits from trees that sustained stem water potentials < -1.5 MPa had 50% less cracking when evaluated using a bench-top immersion assay. Overall, irrigation withholding 5 days prior to harvest was not deleterious to sweet cherry fruit growth or quality. Longer periods of withholding require monitoring tree water status.