Seasonal variation and watering level effect on Lavandula latifolia Medik. essential oil yield and quality

Lavandula latifolia is one of the main aromatic and medicinal plant crops in Spain. Traditionally, the flowering tops of these plants are used for the extraction of essential oils, but to date, the optimal phenological stage for obtaining the maximum yield and quality has yet to be identified. Further, L. latifolia is a rainfed crop, and the scarcity of water resources in the Mediterranean region is having a marked impact on many such crops, implying a significant threat to their survival. The main goals of this study were to explore the combination of these two factors, namely, the optimum stage of harvest and the potential effect of reductions in irrigation on the productivity of these shrubs. For this, selected plants were cloned to establish an experimental crop under three different irrigation levels corresponding to the replacement of potential evapotranspiration in the area (Eto: 0%; 20% and 40%). To monitor seasonal variations in essential oil yield and composition, shrubs were harvested at four different phenological stages of the plant growth cycle: beginning of bloom (Bb); full bloom (Fb); full bloom-beginning of fruit maturation (Fb-Fm) and advanced fruit maturation (Afm). After Clevenger distillation, the oils’ volatile profile was determined by capillary gas chromatography–mass spectrometry analysis. Seasonal variation in essential oil yield and quality showed that the best levels of production were obtained. when L. latifolia was harvested at Fb-Fm, this stage providing the highest relative concentrations of linalool and eucalyptol. These are the components most responsible for the fresh fragrance characteristic of L. latifolia. Moreover, the concentration of camphor, a component related to a pungent fragrance, decreased at the same seasonal stage.

Analyzing the effect of watering level at this phenological stage (Fb-Fm), results showed irrigation equivalent to 40% of Eto was associated with significantly higher essential oil yield and quality. Specifically, the relative concentration of linalool was higher, while that of eucalyptol was lower, and no significant differences were observed in the case of camphor, compared to the composition of the essential oil produced by the control group (0% Eto). To sum up, in the semiarid conditions of the southeast of Spain, the yield and quality of L. latifolia crops improve by irrigating at a rate equivalent to 40% Eto replacement and harvesting flowering tops between full bloom and the beginning of fruit maturation.

Audience Takeaway:

• This study shows the importance of ascertaining both the optimum period for harvesting and how drought level may influence yield and quality of rainfed aromatic and medicinal plant crops, and describes the methods used and results for a specific case, providing a basis for other researchers to explore these parameters for other crops.
• The biological properties of essential oils are directly related to their composition. Thus, knowing that both factors studied -harvesting period and level of watering- can influence essential oil yield and quality, researchers will be able to optimize crop management depending on the intended use.
• There is global concern that climate change, which is associated with increasing temperatures, will lead to more prolonged and severe drought episodes, and in turn, decreased growth and yield of commercial crops.