Differential Effects of Shade on Early-season Fruit and Shoot Growth Rates in `Empire' Apple

Abstract

To determine relative dry-matter partitioning to early-season growth of extension shoots vs. fruits under competitive conditions in the shade, heavily cropping branch sections of `Empire' apple (Malus ×domestica Borkh.) were girdled and shaded to 15%, 40%, and 60% of available light for 9 days, while control branches were girdled and fully exposed. Treatments were applied at both 17 and 27 days after bloom, when fruit diameters averaged 13 and 23 mm, and the number of unfolded leaves on extension shoots averaged 13 and 19, respectively. Fruit diameters, extension shoot lengths, and numbers of unfolded leaves were monitored on the treated branches. Shoot growth was not affected by shading at either growth stage. Fruit growth rate was similar at 100% and 60% available light, but declined 25% at 40% available light and 50% at 15% available light. These results indicate that shoot growth has priority over fruit growth for partitioning in light-limiting conditions early in the season.