Influence of Drought Stress on Growth and Essential Oil Yield of Ocimum Species

Abstract

A pot experiment was conducted to assess the effect of drought stress on growth and secondary compound accumulation of Ocimum species, in a semi-controlled greenhouse during the year 2020. The experiment was performed as a factorial that was based on a randomized complete design with three species of basil namely O. basilicum ‘Genovese’, O. x africanum, and O. americanum, and three levels of water supply (70, 50, and 30% soil water capacity-SWC) that were replicated twice. The results revealed that severe drought conditions (30% SWC) significantly lowered the relative water content and, as a consequence, plants were shorter, narrower in the canopy, and produced smaller leaves which, in turn, resulted in a 50% fresh and dry herb yield loss. Furthermore, severe drought stress negatively affected the essential oil content (except O. x africanum where no change was seen), essential oil yield, and the antioxidant capacity. However, slight enhancements of glandular hair density were observed in the drought treatment than in the control. Regardless of the soil water capacity variation, the major compound of the essential oil and total polyphenol content remained unchanged. Besides drought, morphological and chemical variations were also detected among the Ocimum species. Sweet basil cultivar Genovese produced the maximum biomass (344.7 g/plant) whereas O. x africanum accumulated higher essential oil (2.79%). The major compounds that were identified were linalool in O. basilicum; 1, 8-cineole, and camphor in O. x africanum; and O. americanum had more neral and geranial. In conclusion, a higher water supply is recommended for higher biomass and essential oil yield production in the tested basil species.

Morphological and biochemical responses of selectedOcimumspecies under drought

“…× africanum plants showed a 19% and a 28% reduction in height and diameter, respectively. Previous studies also showed that water shortage significantly decreases the growth parameters of sweet basil cultivars in different growing areas [17,[24][25][26]. In addition, reduced growth as a result of the drought was also reported on O.…”

“…In addition, reduced growth as a result of the drought was also reported on O. × africanum [14,17] and O. gratissimum [13,16]. Almost all the evidence revealed that drought restricted the growth of Ocimum species and other medicinal and aromatic plants.…”

“…The effect of drought on essential oil (EO) content is species-dependent as indicated in Table 4. Drought [17,27,33] also reported different results on the effect of water deficit on the EO content and yield, which could be related to the stress level, the species investigated, and other environmental conditions. On the one hand, an increased EO content as a result of drought stress was observed in O. basilicum [12,24,28], O. americanum [15,29], O.…”

“…Plants are known to undergo biochemical, physiological, and developmental changes as a result of drought stress [11,14,27]. Consequently, several scientists have examined the relationship between water stress and essential oil accumulation in certain Ocimum species, and their results indicated restricted plant growth and slightly enhanced essential oil content [12][13][14][15][16][17]. In contrast, others found that drought stress having no significant effect on the essential oil content of Thymus vulgaris and Hyssopus officinalis [18].…”

Impact of glutamic acid foliar application on sweet basil plants under different irrigation levels in reclaimed land

“…Sweet basil growth and production can be influenced by environmental factors as water stress (Mulugeta and Radácsi, 2022). Water stress have negative effect on photosynthesis, biochemical process, transpiration, stomatal conductance, protein synthesis, antioxidant enzyme activity, osmoprotectants accumulation and biosynthesis of secondary metabolites as volatile oil yield and its constituents.…”