Effects of nano-biofertilizers and NPK application on yield and physiological characteristics of Borago officinalis L. under drought stress

Nano fertilizers prevent the reaction of nutrients with soil by releasing nutrients from nitrogen and phosphorus fertilizers and their uptake by plants. Borago officinalis L. is a medicinal plant of the Borage genus, herbaceous and annual. The leaves of this plant are simple and covered with coarse fibers and its flowers are blue. Borage extracts have excellent antioxidant properties and these effects are related to its phenolic compounds. Drought stress is also one of the most important performance limiting factors in the world. The present study was conducted to investigate the effects of nano-biofertilizers and NPK application on yield and physiological characteristics of Borago officinalis L. under drought stress. The present study was conducted in the form of split plots in a randomized complete block design with three replications in the 2014-2015 crop year at the Agricultural Research Institute of University of Zabol. The main causes of drought stress including: irrigation based on 90%, 70%, and 50% of crop capacity in the entire growth period were examined. Sub-factors of fertilizer application including: no fertilizer application (control), application of 1 kg/ha of nano biofertilizer, application of 5 kg/ha of NPK nano fertilizer and combination of 50% of each were also examined. Other properties such as soluble carbohydrates, percentage of mucilage, phosphorus, potassium, sodium, flavonoids, and antioxidant enzymes including catalase, guaiacol peroxidase and ascorbate peroxidase and dry yield were examined. TDR device was used to apply drought stress. The data were analyzed using SAS software and the means were compared by L.S.D. The results showed that the interaction effect of drought stress and fertilizer on the amount of soluble carbohydrates, potassium, sodium, flavonoids, ascorbate peroxidase and guaiacol peroxidase was significant. As the intensity of stress increased, the amount of carbohydrates, sodium, flavonoids, antioxidant enzymes and mucilage increased and the amount of potassium and dry yield decreased. The application of nano-fertilizers also increased the studied properties. The highest dry yield (2.45 ton/ha) was obtained from the control irrigation area. The highest amount of flavonoids (about 38% more than the control) and soluble carbohydrates (40% more than the control) was obtained from the application of integrated fertilizer treatment at a 50% stress of field capacity. Furthermore, the highest activity of antioxidant enzymes was in severe stress and no fertilizer application. In general, results show that as the drought stress increase, dry matter yield in borage decreases. However, irrigation increased at 90% of field capacity and also with the application of nano-fertilizers dry matter. In general, it can be mentioned that the use of nano-fertilizers moderates the effects of drought stress on borage.