Photoselective nets impact on apple fruit development

To evaluate the effect of the light spectrum on apple fruit carbon partitioning, five light environments were created in a Rosy Glow orchard, in spring 2017. A standard black anti-hail net (serving as control) and four photoselective nets (red, blue, white, yellow) were used to cover 6 trees each. Every treatment was replicated twice; shading was 20% for all nets. Growth of 32 fruit, their bourse shoots and 32 extension shoots was measured twice a week, from the end of April to the end of May, and once a week, until the end of June. Nets induced differences in both fruit and extension shoot growth, but not in bourse shoots. The yellow and the black nets tended to increase growth, while blue appeared to slow it down in absolute terms, but not on per gram basis. The red and white nets were mostly intermediate. As fruit grew at different rates, whereas bourse shoots did not, different source-sink relations between the two are hinted. The bourse shoots borne on the spurs with the more active fruit might have been more efficient, in terms of photosynthate production. On the other hand, fruit might have been stronger sinks, able to draw a higher amount of photosynthates. The light spectrum might induce differences in the carbon loading processes, but the potential applications in the field still need to be tested and further investigations are required.