Can coloured hailnets improve taste (sugar, sugar: acid ratio), consumer appeal (colouration) and nutritional value (anthocyanin, vitamin C) of apple fruit?

Envisaged photo-selective effects, as reported for kiwi and grapevine, of white, red-white, red-black and green-black hailnets were investigated in apple cvs 'Pinova' and 'Fuji Kiku 8' near Bonn, Germany in 2007; uncovered trees served as control. Light transmission of green or red hailnets peaked at 490-610 nm (green) or above 610 nm (red-orange), was reduced by ca. 12% or 14% by white or red-white, respectively, and by 18% or 20% by red-black and green-black hailnets. Air temperature under coloured hailnets was decreased by an averaged 1.3 °C and humidity increased by 2-5% rh. The peel of apples under coloured hailnets contained more chlorophyll (NDVIndex), but 4-5-fold less anthocyanin (NAIndex). The greater sugar (up to 0.7 g/100 g TSS) and acid content, i.e. the better fruit quality and consistent taste (sugar: acid ratio), the firmer fruit (by up to 0.6 or 0.8 g/100 g TSS in 'Fuji' or 'Pinova') with advanced starch breakdown and improved colouration (NAI) under the red-white and white hailnets was attributed to more light than under the red-black and green-black hailnets; hence, white hailnets appear a compromise to obtain good quality and healthy fruit and still protect the plants against sunburn and adverse weather conditions such as hail.