An alternative view on rain-induced cracking of sweet cherries (Prunus avium L.)

Fruit cracking in sweet cherries is unpredictable and is an economically significant problem for growers world-wide. The need for adequate management strategies based on informed risk assessment is clearly evident. Recent resultss from a University of Tasmania project have broadened the understanding of this fruit cracking phenomenon through a number of novel findings. It was discovered that two water uptake pathways result in cherry fruit cracking, and that each pathway results in particular crack types. Current management strategies for fruit cracking focus on water uptake across the fruit skin. Results from this study show that the development of apical and stem end cracks are induced by skin surface wetting, while deep cracks on the side of the fruit are induced by water moving via the vascular system. This new knowledge provides the basis for developing more effective management strategies. The project has further identified that the extent and type of fruit cracking are impacted by variety, season, and crop load. Nine varieties were monitored over four years and it was established that each variety had a particular tendency for crack type. Crop load was negatively correlated with fruit cracking. In addition, the amount or distribution of rainfall in the weeks prior to harvest did not significantly affect cracking incidence, yet season was highly influential, suggesting more than a direct rainfall effect. There are also strong indications that diurnal rhythms, and ambient environmental conditions, play a role in the development of cracking. These findings are important for the development of future cherry fruit cracking management strategies, which may need to be variety specific and encompass whole tree water relations based on the different mechanisms of cracking.