Identification of drought-tolerant nettle populations based on growth performance, physiological responses and phenolic compounds

Nettle (Urtica dioica L.) is widely distributed across temperate regions of the world and is highly beneficial and packed with pharmaceutical value including a rich profile of tannins and terpenoids, organic acids and phenolic compounds. Drought stress is a major limiting factor for the normal performance of various crops worldwide. Among the strategies to mitigate the adverse and damaging effects of drought, the use of drought-tolerant cultivars is considered an effective approach. Accordingly, the effects of three drought stress levels 100 %, 75 %, and 50 % field capacity (FC) on various quantitative and qualitative traits of eight populations of nettle (Babol, Paveh, Mahabad, Siakal, Sardasht, Hamedan, Gorgan, and Nowshahr) were investigated. Analysis of variance revealed significant effects of drought, population, and their interaction on all measured traits. Water deficit reduced shoot and root biomass, plant height, relative water content, and chlorophyll concentration, whereas it increased electrolyte leakage, malondialdehyde, proline accumulation, antioxidant enzyme activities, total phenolic and flavonoid contents, trichome density, and antioxidant activity. HPLC analysis showed that drought stress enhanced the accumulation of key phenolic compounds, including chlorogenic acid, caffeic acid, coumaric acid, and rutin. Correlation analysis highlighted strong positive associations between growth traits, water-related parameters, and chlorophyll content, while oxidative stress indicators were negatively related to biomass. Conversely, antioxidant enzymes and phenolic metabolites were positively correlated with each other and with antioxidant activity. The findings suggest that the Sardasht, Mahabad, and Paveh populations exhibit greater resilience to water limitation and can therefore be regarded as promising drought-tolerant groups. Considering the substantial variation in responses among nettle populations, this research provides a valuable foundation for identifying genetically stable populations with both high productivity and strong tolerance to drought. Such insights can contribute to targeted breeding efforts and support the expansion of nettle cultivation in regions facing water scarcity.