Enhancing the Growth and Chemical Composition of Cardoon Plant by Fertilization with Azolla, Mycorrhizae, Chitosan, and EDTA-Zinc

Due to the limitations and high cost of chemical fertilizers, in addition to their negative effects on medicinal plants—especially pharmaceutical ones—two-season field experiments were conducted in clay loam soil to evaluate the efficacy of azolla, mycorrhizae, chitosan, or EDTA-Zinc on the growth, oil content, and chemical analysis of Cynara cardunculus plants. Azolla, mycorrhizae, and chitosan were applied alone or in combination with EDTA-Zinc. The growth traits were enhanced by foliar application of chitosan in terms of the number of leaves, heads, and seeds per head or plant, as well as chlorophyll content, while fertilization with azolla powder plus EDTA-Zinc resulted in the maximum values of leaf length, flower stem length, fresh leaf weight, and seeds per plant, and significantly improved the oil yield per plant. The highest percent of oil (25.27% and 25.33%) was obtained from seeds of plants treated with mycorrhizae plus zinc in the two seasons. Additionally, the same treatment gave the highest levels of phenolic and flavonoid compounds in cardoon leaves. The major constituents of the fixed oil were linoleic acid, oleic acid, palmitic acid, and stearic acid. The highest amount of unsaturated fatty acids was found in azolla liquid and mycorrhizae treatments. Our findings indicated that the application of azolla, mycorrhizae, and chitosan can be used alone or as a complement to EDTA-Zinc to enhance growth, oil percentage, and oil yield in cardoon plants. Applying these biofertilizers had a significant effect by accelerating plant growth.