Effect of kaolin on productivity, anatomical and biochemical responses to water deficit in Pelargonium graveolens grown in sandy soil

The objective of this study was to examine the response of geranium plants to different irrigation levels (100%, 80%, and 60% based on ET_o) and Kaolin application rates (0, 100, 200 and 300 ppm) during 2022 and 2023 seasons, at Aly Mobarak Experimental Farm, Horticulture Research Station, located at El-Bustan site, El-Behiera Governorate, Egypt, by using a two-way factorial analysis experimental design. The results revealed that water deficit significantly reduced most studied traits. Irrigation level at 60% based on ET_o exhibited poorest performance on growth parameters and decreased fresh yield and essential oil yield by 27.77% 10.73%, respectively as compared with full irrigated plants. However, foliar application of kaolin at 200 and 300 ppm led to increasing biomass accumulation by 28.51, 26.16%, and essential oil yield by 79.51, 89.95%, respectively, as compared with untreated plants grown under the same level of water deficit (60% based on ET_o). GC-MS analysis of essential oil showed that water deficit and kaolin application increased geraniol/citronellol ratio and consequently improved oil quality. Results highlight the positive influence of water deficit and kaolin rates on the development and performance of anatomical parameters. Enzymes assay in leaves revealed in an increase superoxide dismutase (SOD) and peroxidase (POD) activities, and decreased in catalase (CAT) activity under water deficit. As for WUE at 60%, followed by 80% based on ET_o recorded excellent response for geranium plants which led to more water saving. So, it could be concluded that foliar application of kaolin at 200 and 300 ppm obtained the optimal characteristics of geranium plants under experimental conditions. In particular, essential oil yield and productivity.