Water Stress Modifies Essential Oil Yield and Composition, Glandular Trichomes and Stomatal Features of Lemongrass (Cymbopogon citratus L.) Inoculated with Arbuscular Mycorrhizal Fungi

We evaluated the effects of Arbuscular Mycorrhizal Fungi (AMF) on percentage of Essential Oil (EO) content, EO yield, EO composition, and anatomical characteristics of lemongrass at four levels of water availability [100, 75, 50, and 25% Field Capacity (FC)]. EO composition was determined by GC-MS analysis, and scanning electron microscopy was used to investigate the anatomical parameters (stomatal density and size as well as glandular trichomes). EO content and yield significantly increased under moderate water stress (50% FC) and AMF inoculation. The highest EO content (1.09%) and yield (0.26 g plant-1) occurred in 50% FC combined with AMF inoculation treatment. In contrast, the lowest EO content (0.68%) and yield (g plant-1) were observed at 25% FC and no AMF inoculation. The main EO components were geranial, neral, β-pinene and nerol. Water stress increased the content of geranial, β-pinene, whereas it decreased the neral and nerol content. In general, AMF inoculation enhanced the geranial, neral, and β-pinene, but nerol was slightly decreased in total. The highest geranial (48.02%) and β-pinene (7.72%) was observed in AMF inoculated plants at 50% FC. However, the maximum content of neral (35.02%) was found in inoculated plants at 100% FC. Water stress changed the stomatal density and size as well as the number of glandular trichomes. The highest stomatal density was observed in 50% FC (148.1 stomata number mm-2). Water stress decreased the stomatal size, with the lowest stomatal length (24.1 μm) and width (14.1 μm) observed at 25% FC. In addition, the number of glandular trichomes at 50% FC (24.6 trichome number mm-2) was greater than the other treatments. This study suggests inoculating lemongrass plants with AMF and maintaining a moderate water stress to obtain the optimum EO.