Effect of Application of Organic and Biological Fertilizers on Growth and Biochemical Characteristics of Fennel (Foeniculum vulgar Miller) under Greenhouse Conditions

Introduction In recent years, the aggressive application of chemical fertilizers for agricultural production has endangered the health of soil, water, air, as well as crops, and has raised many concerns for the global environment and human health. In addition to the positive biological effects and modification of soil physical and chemical properties due to the gradual release of nutrients, organic fertilizers cause less pollution in the environment. Due to the significant role of medicinal and aromatic plants in different industries, it is important to increasing production of yield and secondary metabolite produced without the use of harmful chemical fertilizers. Fennel (Foeniculum vulgare Mill) is widely grown in arid and semi-arid regions and due to its economic importance and pharmaceutical industrial applications, it is one of the world’s most dimension medicinal plant. This plant has antiseptic, antispasmodic, antiinflammatory, diuretic, carminative and analgesic effects and is effective in gastrointestinal disorder treatment. Moreover with its antioxidant and antiulcer properties, it is used to treat neurological disorders.Materials and Methods This study was conducted to evaluate the effects of organic and biological fertilizers on the morpho-physiological and phytochemical properties of fennel (Foeniculum vulgar Miller). In this study, the impacts of vermicompost (0, 4, 8% in pot), animal manure (0, 7.5, 15% in pot) and mycorrhizal fungi (0, 1%) on physiological and biochemical properties of fennel in greenhouse conditions was evaluated. In order to extract the samples to measure biochemical factors, methanol 70% was used at a ratio of 5:1 (volume- weight). Determination of free radical scavenging was performed by using the DPPH test. The samples’ absorptions were read at a wavelength of 517 nm with Epoch Microplate Spectrophotometer, BioTek Instruments, Inc., USA. Measuring the total phenols was performed according to the Folin’s reagent method and the use of gallic acid as standard (purchased from the brand MERCK, Germany) by using a spectrophotometer at the wavelength of 765 nm. Total flavonoid content was measured using a spectrophotometer at a wavelength of 510 nm through a standard curve of quercetin from Sigma-Aldrich. The Essential oils were obtained from seeds by hydrodistillation for 3 h using a clevenger type device. The analyses of essential oil volatile components were determined by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Data were analyzed by using Duncan’s multiple range test (P< 0.05) by SAS, version 9.4 for Windows.Results and Discussion The results of current investigation showed that organic and biological fertilizers improved the fennel yield and phytochemical properties such as the plant height, seed weight per plant, fresh and dry weight of roots and plants, content of total phenols and flavonoids, antioxidant activity, percentage of essential oil and root colonization. The highest plant height, number of flowers, umbrellas and seeds per plant and fresh and dry weight of roots were obtained after combined application of 8% in pot vermicompost, 15% in pot animal manure and application of mycorrhiza. According to the results, the highest amount of total flavonoids (177.66 mg/100g DW) and root colonization (35.8%) after of 8% in pot vermicompost + 15% in pot animal manure + mycorrhiza application was observed. The results also revealed that the highest fresh and dry weight of the plants (121.33 and 17.41 g, respectively) was obtained after application of mycorrhiza + 15% in pot animal manure. Application of mycorrhiza in combination with 15% in pot animal manure compared to other treatments caused a significant increase in total phenol content in aerial parts with 73.22 mg/100g DW. In addition, the highest amount of antioxidant activity (51%) was obtained after 8% in pot vermicompost + 15% in pot animal manure application. Application of organic and biological fertilizers significantly increased the 1000 seed weight and the percentage of essential oil in fennel. After 15% in pot animal manure treatment, the highest percentage of essential oil by 3.43% was recorded. In general, the highest percentages of essential oil components were related to (E)-Anethole (78.26%), Fenchone (7.15%), Limonene (6.12%) and Methyl chavicol (3.85%), respectively. The amount of (E)-Anethole as the essential oil predominant compound, in the control treatment was 66.92%. The application of mycorrhiza + 4% in pot vermicompost increased the content of (E) -Anethole in essential oil to 80.72%.Conclusion In general, application of vermicompost, animal manure and mycorrhizal fungi improved the growth, biochemical and yield characteristics and essential oil yield of fennel in greenhouse conditions. These fertilizers increased plant yield by providing large amounts of required nutrients and affecting various aspects of root growth and development. Among them, the role of nitrogen may be more prominent due to its participation in protein synthesis and the role of iron in nitrogen fixation, photosynthesis and electron transfer.