3. Colored shade nets and vegetables

and color blush were significantly higher in apples grown under nets compared to uncovered ones in both cultivars.

However, fruit firmness was slightly lower under nets, and no significant differences were reported in terms of sugar content and malic acid between both treatments. (Aoun and Manja, 2020).

Anti-hail photoselective pearl netting of apple trees reduced the incidence of bitter pit by up to 52%, but did not affect the other fruit quality parameters (Candian et al., 2020).

Kiwifruits

Basile et al. (2012) reported high fruit soluble solids content in ‘Hayward’ kiwifruits grown under red colored shade net.

Stone fruits

On the other hand, Giaccone et al. (2012) reported that covering cv. ‘Laura’ nectarine in Italy with white nets, as opposed to red nets, increased fruit sugar content.

The beneficial effects of colored shade nets on above-ground parts of plants have been well investigated, while the root system was neglected.

Citrus fruits

In a field experiment, performed in a 4-year-old orange orchard, Zhou et al. (2018) found significant positive effects of photoselective nets on citrus tree physiological performance by increased photosynthesis rate and vegetative growth. They concluded that a yellow photoselective net had a strong impact on shoot-root interaction and proved equally successful in promoting rapid establishment of young citrus trees.

Avocados

Blue and white (but not red) netting improved the marketable yield, reduced the incidence of anthracnose in ‘Hass’ avocado fruit on the 5th d at shelf-life conditions due to delayed ripening (Tinyane et al., 2018).

3. Colored shade nets and vegetables

Extensive experiments have been conducted to test effects of photoselective nets on vegetable production.

Basil

Basil was grown in the soil under net-house cover by pearl and red nets (50% shade index), or in unshaded condition (open field-control). Light manipulation by colored shade nets also increased antioxidant activity in the leaves. Plants grown under blue shade nets were characterized by the highest eugenol content and highest antioxidant activity (Milenkovic et al., 2019).

Lettuce

Red light influences the production of flavonoids in lettuce leaves (Nsoante et al., 2016). Significantly higher total phenol content was recorded in lettuce plants grown under pearl shade nets and it was accompanied by significantly higher flavonoid content and antioxidant properties in comparison to all other nets (Ilić et al., 2017).

Separately, the influence of colored shade nets (pearl, blue or red with 50% shade) was investigated on quality traits of lettuce cultivars. Pearl net significantly increased carotenoid content in the leaves, while blue shade net retained antioxidants content higher, compared with other nets (Ilic et al., 2019).

However, the concentration of the pigments and phytochemical content depends upon the genotype response to different environmental and light conditions (Pinheiro et al., 2020).

Baby spinach

Baby spinach grown under black netting had less water loss and decay incidence after cold storage at 4°C, while maintaining flavonoid content and antioxidant activity after growing under pearl, red and yellow nets (Mudau et al., 2017).

Peppers

Red bell pepper grown under 35% pearl and yellow shade nets maintained better quality after 16 days at 7°C and three days at 20°C, mainly by reducing decay incidence caused by Alternaria alternata, compared to commercial black and red nets (Goren et al., 2011). No significant differences were observed in percentage of weight loss, firmness and total soluble solids in fruit harvested under the different colored shade nets.

Moreover, pearl and yellow shade nets significantly reduced Alternaria spp. population in the field. The highest Alternaria population was found under the red shade net. The significant low decay incidence in fruit harvested under pearl and yellow shade nets was due to the low inoculum level of Alternaria spp. in the field, and inhibition of fungal sporulation, and/or by a slowing of fruit ripening during its growth as shown by fruit skin colour which was lighter, thus reducing fruit susceptibility to fungal infection in the field.

The significant low decay incidence after harvest was additionally explained by the scattered light, its quality and the ratio between the light spectrum under the two shade nets in the range of blue/UV and the red/far red (Goren et al., 2011).

Alkalai-Tuvia et al. (2014), reported that the lower decay incidence in red pepper under pearl shade net was due to high level of antioxidant activity and carotenoids content that are known to be involved in fruit defense mechanism against decay causing agents. Similar results were reported by Kong et al. (2013) with red pepper grown under pearl shade net.

Bell peppers were grown under black, red, silver and white nets and an unshaded control for 2 years. Use of shade nets increased fruit yield and quality in bell pepper compared with fruit produced in unshaded conditions. Nevertheless, there were no consistent differences between colored nets in fruit total and marketable yield and postharvest fruit transpiration and chemical composition (Diaz-Perez et al., 2020).