Balangu is a medicinal plant consumed in Iranian traditional medicine in the remedy of several nervous, hepatic, and renal diseases. To determine the effects of Myco-Root biofertilizer and chitosan nanoparticles (Cs-NPs) on the physiological and biochemical properties of balangu (Lallemantia iberica) under different irrigation levels, an experiment was laid out as a factorial based on the completely randomized design (CRD) with twelve treatments and three replica-tions. The first factor was represented by different irrigation regimes, including no water deficit (90%FC), mild water deficit (60%FC), and severe water deficit (30%FC); the second factor in-cluded control (no Myco-Root and Cs-NPs), inoculation with Myco-Root biofertilizer, foliar ap-plication of chitosan nanoparticles (Cs-NPs) and co-application of Cs-NPs along with My-co-Root. The results showed that the highest fresh and dry weight, chlorophylls and carotenoids content, chlorophyll index (SPAD) and fluorescence indices were obtained in 90%FC treated with Cs-NPs+ Myco-Root. Besides, the maximum activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and peroxidase (POX) was achieved in 60%FC with application of Cs-NPs+ Myco-Root. Moreover, the maximum essential oil content (1.43%) and yield (0.25 g pot-1) were recorded in 60%FC following the application of Cs-NPs+ Myco-Root. Chemical analysis of es-sential oil showed that germacrene D (31.22-39.77%), (E)-caryophyllene (16.28-19.82%), bicy-clogermacrene (7.1-9.22%) and caryophyllene oxide (3.85-6.96%) were the major volatile constit-uents of balangu. Interestingly, the maximum contents of germacrene D and (E)-caryophyllene were recorded in 60%FC after the application of Cs-NPs+ Myco-Root. Overall, it can be conclud-ed that co-application of Cs-NPs+ Myco-Root could be suggested as a sustainable and eco-friendly strategy for improving the essential oil quantity and quality as well as physiologi-cal characteristics of balangu under water deficit c
