Morpho-physiologic traits in two sage taxa grown under different irrigation regime

Sage is an important aromatic crop, extensively cultivated worldwide. Drought stress affects yield and composition of secondary metabolites such as fatty acids, essential oils, antioxidants, changing the essential oil composition profile with respect to the ISO 9909 standard. Drought tolerance may differ among genotypes, so we compared the response of Salvia officinalis L. and S. officinalis cv. 'Maxima' grown under two different irrigation regimes to highlight differences in leaf growth, water potential, gas exchange and essential oil composition. Potted plants were grown in the greenhouse at 100% or 50% of field water capacity for three months. Monthly measurements of 3rd node leaf length, width and area were taken using ImageJ software. Midday leaf water potential was measured using a pressure chamber and leaf stomatal conductance, transpiration and net photosynthesis were measured using a portable infrared gas analyzer. Essential oil composition was determined by gas chromatography and mass spectrometry. Drought stress reduced leaf area in both taxa, but the effect was less pronounced in S. officinalis than in S. officinalis cv. 'Maxima' (-30%). Leaf water potential was slightly lower in the latter cultivar than in S. officinalis under water deficit. In irrigated S. officinalis cv. 'Maxima' plants transpiration and stomatal conductance rates were more than twice those of S. officinalis, while under water deficit the difference between the taxa was not significant. Interestingly, net photosynthesis in S. officinalis was about twice that measured in S. officinalis cv. 'Maxima', both in irrigated and in stressed plants. Furthermore, in S. officinalis water deficit resulted in a slight reduction of photosynthetic rate, while in S. officinalis cv. 'Maxima' the reduction was around 50%. Both taxa were affected by drought stress, responding with a reduction in leaf expansion and in transpiration, in order to reduce water loss. However, S. officinalis appeared to have a greater efficiency, maintaining higher levels of carbon assimilation.