Influence of shading treatment on yield, morphological traits and phenolic profile of sweet basil (Ocimum basilicum L.)

We investigated the roles of different shading strategies on plant growth, antioxidant activity and phenolic profile of sweet basil (Ocimum basilicum L.), a widely used herb with culinary and medicinal properties. Sweet basil plants were cultivated in a commercial multi-span tunnel-greenhouse covered with an EVAC plastic film, shaded from solar radiation in five different ways: n. 1, by calcium hydroxide whitening; n. 2, installing up - or n. 3, under - the greenhouse roof, a PE-HD white reflective net with 36% shading factor; n. 4, installing up - or n. 5, under - the greenhouse roof, a PE-HD white reflective net with 58% shading factor. The remaining part of the greenhouse (n. 6 - control) was unshaded. In each trial, yield traits, antioxidant activity and contents of phenolics of sweet basil plants were assessed to evaluate the influence of the shading strategy on these parameters. The antioxidant capacity was evaluated by using three different in vitro assays: DPPH scavenging activity, reducing power (FRAP) and lipid peroxidation inhibition (BCB). To compare the data obtained by the different chemical methods, the relative antioxidant capacity index (RACI) was calculated. The yield was highest in unshaded plants. The control trial, in which the incoming solar radiation was filtered only by the film which covers the greenhouse, showed the highest RACI value (0.98), indicating that the antioxidant capacity was probably influenced by higher light and temperature conditions. Phenolic quantification, determined by HPLC-DAD, enabled to observe a correlation between the antioxidant power and the identified metabolites.