Effect of Rain Cover on Tree Physiology and Fruit Condition and Quality of 'Rainier', 'Bing' and 'Sweetheart' Sweet Cherry Trees

A study was conducted in a commercial sweet cherry orchard in central Chile. The objective was to evaluate the rain cover effect on changes in the microclimate, vegetative growth, plant physiology and fruit quality of 'Rainier', 'Bing' and 'Sweetheart' sweet cherry trees. The data were compared to a control without a rain cover. The results showed that, under the rain cover, there was a 50-60% reduction in total solar radiation, as well as an increase in air temperature (+0.6 degrees C) and a decrease in relative humidity (-4.7 percentage points) in the upper canopy zone. Regarding the trees under rain cover, a greater shoot length (28-58%) and leaf area (24-54%) were observed among cultivars compared to the control; the trunk cross-sectional area was only significant in 'Rainier', it being 1.2 times greater under rain cover. CO2 assimilation showed no differences, but an increase in the leaf transpiration rate was observed. The fruit firmness and sugar content in fruits were negatively affected by the rain cover, those characteristics being of major relevance for the cherry growers. Additionally, the contents of anthocyanins and carotenoids and the antioxidant capacity were significantly lower only in 'Rainier' under rain cover, while the total phenol content decreased in all three cultivars. The rain cover did not negatively affect the tree physiology, but it can be detrimental in bicolor cultivars with a yellow flesh due to a lower color and phenolic compounds development.