Colored shade nets and different harvest times alter the growth, antioxidant status, and quantitative attributes of glandular trichomes and essential oil of Thymus vulgaris L.

Abstract

Its popularity in Mediterranean cuisine and gastronomy in general, as well as its medicinal and aromatic value, contributes to the high demand for Thymus vulgaris L. (thyme). Light is the source of energy, a signaling agent for growth, and a modulator of physiological responses in plants. The objective of this study was to evaluate the effects of cultivating T. vulgaris in tropical conditions under differently colored shade nets on vegetative growth, photosynthetic pigments, antioxidant activity, and quantitative and qualitative characteristics of its essential oil (EO) in two seasons. The treatments were cultivation in sunlight and under blue, black, and red nets in tropical conditions in the fall and spring seasons. The plants were harvested 100 days after transplanting. Leaf, stem, root, and total dry weight were evaluated; photosynthetic pigments and nonenzymatic antioxidant activities were quantified; and parameters related to the production of EO were determined. With the exception of chlorophyll a, carotenoids, and some EO chemical compounds, the cultivation of thyme in the spring brought significant gains to the plants regardless of the light conditions. The cultivation of T. vulgaris under sunlight produced an increase of up to 82.2 % in dry weight and 639 % in EO yield compared to cultivation under nets. It also supported the highest antioxidant activity, regardless of the growing season. On the other hand, cultivation under sunlight provided the lowest chlorophyll a and b and thymol contents. Thus, cultivation in the warmer seasons and under full-sun conditions are the best options for cultivating T. vulgaris in a region with a tropical temperate rainy climate (mesothermal).