Co-application of arbuscular mycorrhizal fungi and putrescine improves essential oil production and drought tolerance in Cuminum cyminum L.

In response to the increasing challenges of climate change, water scarcity, and the growing demand for medicinal plant products, research has growingly focused on enhancing drought tolerance within sustainable and environmentally friendly farming systems. Organic farming systems, in particular, require a comprehensive understanding of plant responses to stressors and the optimization of these systems for maximum productivity. To date, no investigation has been conducted into the combined effects of polyamines (PAs), specifically putrescine (Put), and arbuscular mycorrhizal fungi (AMF) on the essential oil (EO) content and composition of Cuminum cyminum L. under drought stress. This study aimed to evaluate the effects of AMF, Put foliar application, and their combination on EO yield, chemical composition, and physiological parameters such as chlorophyll (Chl) and carotenoid content under optimal and drought stress conditions. Results demonstrated that foliar application of Put and AMF inoculation significantly (P < 0.05) increased seed yield (by 45.4 and 14%, respectively), EO content (by 24.9% and 8%), EO yield (by 78.1% and 23.8%), Chl a (by 67.2% and 28.5%), Chl b (by 28.7% and 15.8%), total Chl (by 31.8% and 23.5%), and carotenoid levels (by 13.3% and 9.5%) under both optimal and drought conditions. Moreover, treatments with AMF and Put modulated EO composition, increasing the concentrations of cuminaldehyde (by 23.4% and 17.3%), limone (by 19.3% and 7.4%), and β-pinene (by 29.9% and 12.5%), while decreasing γ-terpinene (by 53.3 and 31.8%), o-cymene (by 35.3% and 17.1%), and linalool (by 32.8% and 55.8%) compared to untreated controls. The combined application of AMF and Put produced the highest improvements in EO content, yield, Chl a, Chl b, total Chl, and carotenoids, while also increasing catalase activity, proline, and total phenol content under both optimal and drought stress conditions. These findings suggest that the co-application of Put and AMF significantly improves drought tolerance in field-grown cumin. Further molecular studies are warranted to elucidate the mechanisms underlying AMF-Put interactions, which could potentially optimize EO yield and modify its specific composition.