Rain cracking limits sweet cherry production worldwide. Cracking is often assessed in laboratory assays, where detached fruit is submerged in water. Scientists at Leibniz University Hannover compared cracking of detached fruit that were submerged in water with fruit that remained attached to the tree, but were exposed to simulated rain or fruit that were detached, placed in a wire cage and positioned in the canopy and were exposed to simulated rain. For the study, water uptake and cracking were determined in detached and attached fruit.
Results showed that the rates of water uptake were highest in detached, submerged fruit, were intermediate in attached fruit exposed to simulated rain and least in detached fruit in a wire cage exposed to simulated rain. The percentage of cracked fruit increased sigmoidally with time and the attached fruit cracked less and more slowly than fruit submerged in water. Cracking was markedly faster in detached, submerged fruit, than in still attached fruit, than in detached fruit in a cage.
When the percentage of cracked fruit was expressed as a function of the amount of water taken up revealed that the detached, submerged fruit generally required less water uptake than attached fruit or detached fruit in a wire cage. Attached fruit cracked mostly in the pedicel cavity region whereas detached submerged fruit cracked mostly in the stylar scar region. Wetness duration was longest and area wetted largest in detached, submerged fruit, followed by attached or detached fruit exposed to simulated rain, thus we can conclude that sweet cherry cracking is caused by duration and surface wetness and not by water uptake".
Source: Andreas Winkler, Isabell Blumenberg, Lucas Schürmann, Moritz Knoche, 'Rain cracking in sweet cherries is caused by surface wetness, not by water uptake',
2020, Scientia Horticulturae, Volume 269.