Putrescine Increases Frost Tolerance and Effectively Mitigates Sweet Cherry (Prunus avium L.) Cracking: A Study of Four Different Growing Cycles

Sweet cherry producers must deal with different climactic challenges annually, specifically the impact of spring frost and the inherent risk of fruit cracking. This susceptibility arises from the simultaneous occurrence of spring frost during the bloom stage or the sweet cherry cracking at vulnerable maturity stages in sweet cherry trees during persistent rainfall. Given the change in climatic patterns, the implementation of new strategies and innovative approaches becomes imperative to alleviate potential damage from these climatic adversities. This study aims to explore-for the first time-the effectiveness of preharvest putrescine applications during the flowering stage and ripening on-tree to increase tolerance in sweet cherry against adverse climatic events throughout its on-tree development and at the time of harvest. In this context, foliar applications of putrescine at concentrations of 1 and 10 mM were administered to distinct sweet cherry cultivars, namely, 'Prime Giant' and 'Sweetheart'. Over the course of four growing seasons, our investigation focused on evaluating the influence of this natural elicitor on the frost resilience of flower buds during the preharvest period and its impact on reducing fruit cracking in these selected cultivars. In this sense, the overall malondialdehyde content exhibited a reduction in flower buds treated with putrescine, and the fruit set experienced an increase across the majority of evaluated growing seasons. On the other hand, the incidence of sweet cherry cracking in putrescine-treated sweet cherries showed a consistent reduction in all the studied growing seasons. Our results indicate that preharvest treatments with putrescine effectively alleviate the susceptibility of flower buds to spring frost and significantly diminish fruit cracking, thereby enhancing the overall tolerance to abiotic stress. Furthermore, we evaluated different quality parameters at the time of harvest, including fruit firmness, external color, total soluble solids, and total acidity. Generally, the observed changes in these parameters were delayed in putrescine-treated fruit as compared to the control batch or remained unaffected. For this reason, the implementation of preharvest treatments based on putrescine emerges as a valuable strategy for adapting to climate change and mitigating the impact of abiotic stress, potentially increasing sweet cherry production.