Introduction

Drought is one of the most important environmental stresses limiting plant growth, development, and productivity. The expansion of drought-prone areas and the increasing scarcity of water resources have drawn researchers’ attention to strategies for reducing the adverse effects of water deficit on crop performance. Among the sustainable approaches to enhancing plant tolerance to drought stress, organic and biological fertilizers have received particular attention because of their beneficial effects on soil properties, nutrient availability, and plant physiological responses. The use of these ecological nutrient inputs may provide an effective approach to managing plant nutrition and developing sustainable agricultural systems under water-limited conditions. Therefore, this study aimed to evaluate the effects of ecological nutrient inputs on selected traits of Persian borage (Echium amoenum Fisch. & C.A. Mey.) in response to drought stress.



Materials and Methods

A two-year field experiment was conducted during the 2020–2021 and 2021–2022 growing seasons in Noorabad Mamasani County, Fars Province, Iran. The experiment was arranged as a split-factorial design within a randomized complete block design with three replications. Irrigation regimes were assigned to the main plots at three levels: no drought stress, with 100% of the crop water requirement supplied; mild drought stress, with 75% of the crop water requirement supplied; and severe drought stress, with 50% of the crop water requirement supplied. The subplot treatments consisted of a factorial combination of two mycorrhizal inoculation levels (without inoculation and inoculation with Funneliformis mosseae) and five nutrient treatments: an unfertilized control, livestock manure compost supplying 100% of the crop nitrogen requirement, zeolite-enriched livestock manure compost supplying 100% of the crop nitrogen requirement, zeolite-enriched livestock manure compost supplying 50% of the crop nitrogen requirement, and chemical N–P–K fertilizer. The measured traits included leaf physiological characteristics (relative water content, electrolyte leakage, and malondialdehyde content), flower biochemical characteristics (anthocyanin content and reducing power), and yield-related traits (number of flowers per plant and dry flower yield).



Results and Discussion

The three-way interaction among irrigation regime, mycorrhizal inoculation, and nutrient treatment significantly affected only dry flower yield in both growing seasons. Increasing drought severity increased leaf electrolyte leakage, malondialdehyde content, flower anthocyanin content, and reducing power, while decreasing leaf relative water content and the number of flowers per plant. The application of livestock manure compost and mycorrhizal inoculation increased leaf relative water content, flower anthocyanin content, reducing power, the number of flowers per plant, and dry flower yield, but decreased leaf electrolyte leakage and malondialdehyde content. Among the nutrient treatments, zeolite-enriched livestock manure compost supplying 100% of the crop nitrogen requirement had the greatest effect, followed by livestock manure compost supplying 100% of the crop nitrogen requirement. The highest dry flower yield, one of the most important economic traits of Persian borage, was obtained under full irrigation combined with mycorrhizal inoculation and zeolite-enriched livestock manure compost supplying 100% of the crop nitrogen requirement.



Conclusion

Overall, the results showed that the combined application of mycorrhizal inoculation and organic fertilizers improved the physiological, biochemical, and yield-related traits of Persian borage and contributed to greater plant tolerance to water deficit.