Crop yield response to water - Cra

The fruit with fleshy pericarp is classified as a drupe and is single-seeded. Fruit growth followsthe typical double-sigmoid pattern, with rapid exponential growth during the cell divisionphase (Stage I, ~ 30 days in length), followed by a relatively short period of slow growth duringpit hardening and embryo development (lag phase, Stage II). Finally, a second period of rapidcell and fruit enlargement prior to harvest (Stage III), when the fruit can increase in size ca. 40-60 percent, although this is linked to accumulated heat units (degree-days) after flowering, ina similar fashion to other Prunus species (DeJong and Goudriaan, 1989). Therefore, the lengthof each stage varies with variety and location. During the postharvest period, some shootgrowth and carbohydrate storage for reserves are the primary sinks for carbon assimilation,which continues until leaf fall.Effects of Water DeficitsA distinction should be made between plums for fresh fruit production and those for driedfruit production (prunes), as dry matter accumulation is less sensitive to water stress thanis the increase in fresh weight, particularly during the last stages of fruit development. Inaddition, lower fruit hydration rates resulting from water deficits may also offer an advantagefor post‐harvest fruit processing in the case of prunes for dry fruit production (Lampinenet al., 1995). Thus, prune trees are considered to be moderately resistant to water stress,as indicated by early experiments (Hendrickson and Veihmeyer, 1945) in the deep soils ofCalifornia’s Sacramento Valley, where it took 4 years of no irrigation to detect decreased trunkgrowth, and 5 years of water deprivation to detect a significant reduction of fruit yields. Thisis also supported by more recent findings (Goldhamer et al., 1994) where irrigation cutoff, upto 37 days before harvest did not have any negative impact on dry fruit yields of French prune.Water stress during fruit growthIn Japanese plums for fresh markets, water stress in the final stages of fruit growthsignificantly decreased fruit size, but accelerate ripening and lead to an increase in fruitsugar concentration (Naor, 2004). Under water stress, average fruit weight and yield wereaffected by increased tree crop load for Japanese plum (Intrigliolo and Castel, 2005; Naor,2004) but under minimum stress conditions, the fruit size distribution was unaffected by fruitnumber per tree, possibly because of low crop yields, which did not introduce significantlimitation of assimilates (Naor, 2004). Irrigation of previously water-stressed prune treeshas been found to induce fruit-end cracking (Uriu et al., 1962); the formation of cracks wasaccompanied by increased osmotic potential gradients along the fruit in re-watered trees(Milad and Shackel, 1992).Water stress during postharvestThe practice of reducing or eliminating irrigation after harvest of an early-maturing plumcultivar (P. salicina) irrigated with foggers was studied in California (Johnson et al., 1994),where completely cutting off irrigation led to partial defoliation within a few weeks andloss of yield in the subsequent year. Postharvest midday stem-water potential (SWP) reached~-3.3 MPa with no symptoms of defoliation in Black Amber (Naor, 2004). For trees that wereirrigated daily, but at half the rate of the fully irrigated control, no reduction of yield orfruit quality occurred over a 3-year period, possibly because of the contribution of stored350crop yield response to water