The effect of shading (i.e. reduction of sunlight availability) on fruit growth physiology has been widely studied in apple
(
Malus domestica
Borkh.), but little knowledge exist about fruit growth responses to changes in the light spectrum. The
aim of the present research was to study the effect of use of colored nets with differential sunlight transmission in the
blue (B, 400-500 nm), red (R, 600-700 nm) and far-red (FR, 700-800 nm) spectra on apple fruit growth and physiological
associated responses. Three year old 'Fuji' apple trees were covered with 40% photo-selective blue and red shade nets, 40%
neutral grey shade net, and 20% neutral white net as control. Red and blue net reduced in the same proportion (27%) the
photosynthetically active radiation with respect to control. However, blue net increased by 30% and reduced by 10% the
B:R and R:FR the light relations, respectively. Maximal fruit growth rate under blue and grey nets was 15-20% greater than
control. Fruit weight under blue net was 17% greater than control, but no significant differences in fruit weight were found
among red net and control. Leaf photosynthesis and total leaf area under blue net were 28% and 30% higher than control,
respectively; with ensuing positive effect on tree net C assimilation rate and total dry matter production. Results suggest that
shifting the B, R, and FR light composition with photo-selective nets could be a useful tool to manipulate the photosynthetic
and morphogenetic process regulating the carbohydrate availability for apple fruit growth.
