Environmental Changes Under Hail Protective Nets With Different Colouration Affect Fruit Quality

The quality of fruits and their nutritious value are established on the tree and influenced by the orchard environment. The increase in hailstorms, attributed to global climate change, has resulted in the installation of either black or white hailnets in fruit orchards worldwide as a sustainable measure to ensure fruit production. Coloured hailnets have been available from 2007 with suggested effects of their photoselective light transmission on photosynthesis, yield, fruit quality and fruit colouration. The objective of the present work was to investigate these effects with a range of red and green hailnets on apple trees near Bonn, Germany; uncovered outside trees served as control. Photosynthetic active radiation (PAR) was reduced by c. 12 or 14% by white or red-white, respectively, and by 18 or 20% by red-black and green-black hailnets. The peel of apples under coloured hailnets contained more chlorophyll (NDVIndex), but 4-5-fold less anthocyanin (NAIndex) than fruit outside. Fruits under coloured hailnets were less firm (by up to 1.5 kg/cm2 in 'Pinova' and by up to 0.4 kg/cm2 in 'Fuji'); these apple fruit were up to 0.5% TSS less sweet, less ripe and contained less malic acid, with 31-42% less vitamin C than those outside, without alterations to sugar:acid ratio. The larger sugar and acid content, i.e., the better fruit quality and consistent taste (sugar:acid ratio), the firmer fruit with advanced starch breakdown i.e. improved consumer eating quality and colouration under the red-white and white hailnets was attributed to more light than under the red-black and green-black hailnets. Overall, the greatest concentrations of all fruit constituents including red colour pigments (anthocyanin) came from unprotected trees outside.