Water-soaking and cracking in strawberry: Mechanism and causes

• Applicant: Professor Dr. Moritz Knoche
• Subject Area: Plant Cultivation, Plant Nutrition, Agricultural Technology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426627435

• Final Report Year: 2023

Final Report Abstract

The results obtained may be summarized as follows: Strawberries have an exceptionally thin cuticle. Cutin and wax synthesis ceases at the onset of color change. The subsequent increase in surface area distributes a constant amount of cuticle over an enlarging surface. As a consequence, the fruit cuticle is markedly strained. – The strain of the cuticle results in numerous microcracks. Location and orientation of microcracks suggest that these cracks result from growth stress. The depressions of the achenes, the base of trichomes and the abscission zones of petals are preferential sites of microcracking. Like in many other fruit crops, exposure of the strained fruit surface to water aggravates microcracking. – The strawberry fruit skin has the highest permeability in water uptake and in transpiration among the fruit crop species investigated so far. The high permeability results from a high density of microcracks. Selective sealing of the calyx region using silicone rubber reduced water uptake. – The water inflow through the xylem of the pedicel decreases in the course of development, whereas the inflow via the phloem increases. – Water soaking is an important surface disorder of strawberries. Symptomatic fruit show pale, deliquescent patches of skin. This damage extends into the flesh. Numerous cuticular microcracks occurred in water-soaked areas. Water soaking occurred only if the skin was exposed to liquid water. Water soaking was more rapid when the cuticle had been abraded. Water soaking involves cuticular microcracking, localised water uptake, bursting of cells and the release of organic acids into the apoplast. The damage propagates from cell to cell. – Incubating fruit in solutions of divalent and of trivalent cations decreased water soaking. Reduced water soaking by CaCl2 was due to decreasing cuticular microcracking, to decreasing leakage of plasma membranes and, possibly, to increased crosslinking of cell wall constituents. – Cracking is another important disorder caused by rain. Cracking is more common in necked than in normal-shaped fruit. Most macroscopic cracks (‘macrocracks’) occur in the seedless neck. Large fruit is more cracking susceptible than medium size or small fruit. Macrocracks are highly oriented suggesting a relationship with growth stress and strain.

Publications

• Strawberry fruit skins are far more permeable to osmotic water uptake than to transpirational water loss. PLOS ONE, 16(5), e0251351.
  Hurtado, Grecia; Grimm, Eckhard; Brüggenwirth, Martin & Knoche, Moritz
  
• Water Soaking Disorder in Strawberries: Triggers, Factors, and Mechanisms. Frontiers in Plant Science, 12.
  Hurtado, Grecia & Knoche, Moritz
  
• Xylem, phloem and transpiration flows in developing strawberries. Scientia Horticulturae, 288, 110305.
  Winkler, Andreas; Hurtado, Grecia & Knoche, Moritz
  
• Calcium ions decrease water-soaking in strawberries. PLOS ONE, 17(8), e0273180.
  Hurtado, Grecia & Knoche, Moritz
  
• Detached, wetted strawberries take up substantial water in the calyx region. Scientific Reports, 13(1).
  Hurtado, Grecia & Knoche, Moritz
  
• Microcracking of strawberry fruit cuticles: mechanism and factors. Scientific Reports, 13(1).
  Hurtado, Grecia & Knoche, Moritz
  
• Necked strawberries are especially susceptible to cracking. PeerJ, 11, e15402.
  Hurtado, Grecia & Knoche, Moritz