Abstract

Gradual warming during winter is critical for temperate fruit species with high chill accumulation requirements, such as sweet cherry. Currently, farmers use chemical rest breaking agents (RBAs) like Hydrogen Cyanamide (HC). However, these are only effective if a minimum threshold of chill accumulation is satisfied. According to recent reports, temperatures are expected to rise, especially in temperate regions. Therefore, technologies are required to increase the efficiency of chill accumulation without losing productivity and profitability of perennial fruit systems. This work aimed to determine the effect of shading on chill accumulation in sweet cherry cv. Santina in the Central Valley of Chile. Two trials were established with two treatments each: a control (full sun) and a shading treatment (under a shade cloth). In trial 1, the shade cloth was installed on a high tunnel structure, while in trial 2, it was over a gable roof structure. Prior to HC application, branches were collected from 6-10 trees per treatment and taken to a growth chamber to force them to resume growth. After 10 days of forcing, reproductive spurs were counted. In the orchard, the trees applied with HC were also monitored during budbreak. Results indicate that slight changes in air temperature due to shading do not allow to confirm consistently increased chill accumulation (portions, hours, or units). Nevertheless, relevant differences in spur temperature were observed. Shading cloth affected the proportion of active spurs after forcing time and in the field. Shaded buds showed more winter chill accumulation, possibly due to lower spur temperature. Artificial shading could enhance winter dormancy in sweet cherry crops, aiding RBAs applications in temperate zones with reduced chill due to climate change. However, it is necessary to improve our understanding of how different types of structures influence the microclimate of protected crops.