The possibility for improvement of flowering, corm properties, bioactive compounds, and antioxidant activity in saffron (Crocus sativus L.) by different nutritional regimes

Saffron as one of the most precious spices and medicinal plants, is highly valued for its bioactive compounds. Quantity and quality in spices and medicinal plants can be improved by the plant nutrition. In this field study the sole and integrated application of various fertilizers types and arbuscular-mycorrhizal fungus (AM), Glomus mosseae with respect to the flower-related traits, corm properties, quality, bioactive compounds and antioxidant activity of saffron at Kerman region, Iran was examined over a three years period. The fertilizer treatments comprised control (non-amended soil); 20 Mg ha−1 compost; 10 Mg ha−1 compost+ 8 Mg ha−1 biochar and chemical fertilizers. In each fertilizer treatment, planting bed was inoculated or non-inoculated with AM. The results showed that during the first flowering period (2015–16), neither AM nor fertilizer types affected flowering. Inoculation with AM particularly in the application of fertilizer treatments through positive effects on different corm properties during the vegetative growing seasons of 2015–16 and 2017–18, improved flower-related traits in the next flowering periods of 2016–17 and 2017–18. Picrocrocin and safranal content as well as total phenolic content and total flavonoid content in tepals were considerably enhanced by organic amendments and chemical fertilizers compared with the control. While the total phenolic content in stigmata was reduced by AM-inoculation, the total flavonoid content and antioxidant activity of stigmata and tepals were not significantly influenced. Principal Component Analysis clearly discriminated the integrated nutritional treatments from the sole ones based on flower-related traits and corm properties which were positively related with integrated treatments. Organic amendments were characterized by a higher total phenolic content and antioxidant activity in stigmata. Chemical fertilizers alone or in AM-inoculation associated with quality attributes and total flavonoid content in tepals. Research findings confirmed that the integrated application of mycorrhizal fungus, organic, and chemical fertilizers significantly influences the overall production of saffron.