Diurnal and Seasonal Growth Responses of Apple Trees to Water-Deficit Stress

This study was conducted at the Station Experimentale Fruits et Legumes in the South-East Mediterranean region of France and aimed to explore the effects of water-deficit stress on fruit production, water status, and growth responses. It was carried out on a 9-year-old top worked apple cv. "Joya (TM)" on Pajam-1 rootstock. Water stress (at 50%) applied after vegetative growth was completed, from the beginning of July to the end of the irrigation season decreased size but increased soluble solids content in fruit. Water-stressed trees showed relatively high water use efficiency without causing a significant effect on yield. Indeed, the water amount used for one fruit was 11.41 (median) in water-stressed trees and 15.91 (median) in well-watered trees, although tree volume and leaf area were similar between the two water regimes. A within-tree network of dendrometers was installed in four locations (bottom of a branch and end of the same branch, fruit, and trunk). The branch and trunk's maximum and minimum diameter growth were observed in the morning and noon, respectively, over the diurnal period, whatever the water regime. The maximal diameter growth of fruit in both water regimes was during the afternoon on a diurnal basis, unlike vegetative tree portions.