In apple production, the incidence of hailstorms during the growing season is high in some regions. The damage to leaves caused by hail decreases photosynthesis, causes damage to the fruit during the growing season (Tartachnyk and Blanke, 2002), and is an infection entry point for diseases such as fireblight. To protect the assimilation area and ensure high fruit quality, apple trees are increasingly grown under hail nets. The nets used for protection against hail represent an additional investment (Stampar et al., 2002).
Several different types of nets are used to protect fruit crops against hail. In European fruit orchards, most of the hail nets used are black, some white, and since 2007 colored (red and green) (Blanke, 2007) hail nets have also become available. However, on a sunny summer day, light intensities under the hail nets are lower compared with the outside control (Solomakhin and Blanke, 2008). Black hail nets greatly reduce incident solar light, and they may have a negative impact on fruit development and on the final color of fruit (Guerrero et al., 2002; Stampar et al., 2002). Fruit grown under these hail nets suffers from lower fruit quality, i.e., less (red) coloration, less firm fruit flesh, less sugar, and therefore less taste (Funke and Blanke, 2005). White and colored hail nets reduced light less than black hail nets and the black hail nets decreased fruit coloration in the poorly colored apple cultivar Pinova more than white and colored (Blanke, 2007).
Reflective white woven cloth placed in the grass alleys between the tree rows under the hail net can overcome these shortcomings (Funke and Blanke, 2005). Relative to the grassed control, two tested reflective cloths increased the percentage of Class I fruit with greater than 25% coloration by 12% (from 82% to 94%) without hail nets and by 23% (from 69% to 89%) under hail nets (Solomakhin and Blanke, 2007). Reflective foil appears to be a method for increasing red skin coloration in ‘Gala’ apples (Layne et al., 2002). Glenn and Puterka (2007) reported that the use of reflective, aluminized plastic film increased fruit red color and that the use of reflective, particle films increased average fruit weight. These mulches reflect solar radiation into the tree canopy and may increase canopy absorption of photosynthetic photon flux by up to 40% (Green et al., 1995). This additional light is useful for both photosynthesis and anthocyanin pigment production (Jakopic et al., 2007; Layne et al., 2002). Although the red color of apple fruit is determined by the concentration of anthocyanin in the fruit peel, it is also affected by concentrations of other pigments like flavonoids, chlorophyll, and carotenoids (Lancaster, 1992). A variety of red colors are produced by cyanidin glycosides copigmented with flavonols and other compounds (Lancaster, 1992).
Apple fruit is known to be rich in flavonoid compounds such as anthocyanins, dihydrochalcones, quarcetin 3-glycosides, catechin, and epicatechin and its polymers, which are mainly located in the skin (Awad et al., 2001; Lata et al., 2009). Polyphenols are a major antioxidant in apples. Antioxidants scavenge and neutralize free radicals, which in turn play a role in the onset of cardiovascular disease and cancer (Biedrzycka and Amarowicz, 2008). The main anthocyanin pigment is cyanidin 3-galactoside, which can scavenge superoxide radicals in an in vitro system (Yamasaki et al., 1996).
One factor among those that may affect the concentration of phenolic components in apples is light exposure (Awad et al., 2000). Flavonoid and chlorogenic acid contents in fruit vary greatly among cultivars, orchards, positions within the tree, and even within individual fruit (Awad et al., 2000).
Jakopic et al. (2007) demonstrated that light use of ‘Fuji’ apple trees grown under hail nets could be improved using reflective groundcover, resulting in better fruit coloration. The objective of the present work was to evaluate the effect of netting and reflective foil on the contents of individual phenolics compounds. We measured changes in the concentrations of four cyanidin glycosides, seven quercetin glycosides and aglycone quercetin as well as catechin, epicatechin, and chlorogenic acid as a result of the lighting changes created by hail nets and reflective foil.
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