Rain damage in strawberries: identifying the drivers and understanding the mechanisms

Abstract

Strawberries are extensively cultivated and enjoyed for their appealing sensory attributes and nutritional benefits. Rain can significantly reduce its quality. Rain damage is characterized by water soaking and cracking. Both disorders increase the risk of decay, causing significant economic losses. The objectives of this study were (1) to identify the mechanisms and factors of water movement through the fruit’s surface, (2) to characterize and to identify the factors affecting microcracking of the cuticle, (3) to identify the mechanism and the factors affecting cracking in strawberry, (4) to identify the triggers, factors, and mechanism of water soaking in strawberry and (5) to establish the effects of calcium (Ca) and other monovalent, divalent, and trivalent cations on water soaking.

Permeances for osmotic water uptake and transpiration were higher than in other soft fruit. High osmotic uptake permeance may be attributed to a thin cuticle and viscous water flow through microcracks and polar pathways. The abscission zones of the petals and stamina, and microcracks in the calyx and receptacle served as preferential pathways for osmotic uptake. Microcracking increased with fruit development, and it was significantly promoted by surface wetness. Necked strawberries were more susceptible to cracking than normal-shaped fruit. Growth strain was the main driver of cracking, and this was further exacerbated by water uptake. Water-soaked fruit showed show pale, deliquescent patches of skin. Water uptake markedly increased water soaking. Citric and malic acids increased plasma membrane permeability and increased water soaking. Cuticular microcracks were observed in water-soaked areas. Ca mitigates water soaking by decreasing cuticular microcracking, leakage from plasma membranes, and possibly increased cross-linking of cell wall constituents. Rain damage in strawberries involves cuticular microcracks, localized uptake by viscous flow, cell bursting, and release of organic acids in the apoplast. These events trigger a chain reaction that extends a microcrack into a macrocrack and, as skin cell destruction progresses, causes water soaking.