Exogenous salicylic acid stimulates physiological and biochemical changes to improve growth, yield and active constituents of fennel essential oil

Abstract

Fennel (Foeniculum vulgare Mill) is a high-value medicinal and essential oil bearing plant used extensively in pharmaceutical, food and cosmetic industries. A pot experiment was carried out in the natural conditions of net house to resolve whether the foliar application of salicylic acid (SA) might enhance the growth, yield and essential oil production of fennel. Plants were sprayed three times with SA. The first spray was carried out at 40 days after sowing (DAS); the second and third sprays were applied one and 2 weeks later, the plants were sprayed with deionised water (control) and different concentrations of SA (10−5, 10−4 and 10−3 M). The foliar spray of SA at 10−4 M significantly enhanced the vegetative growth (shoot and root lengths, fresh and dry weights), physiological and biochemical characteristics (chl ‘a’, chl ‘b’, total chlorophyll and carotenoids contents, nitrate reductase activity, carbonic anhydrase activity, leaf-N, -P and -K contents), yield characteristics (number of umbels and fruits, 1,000-seed weight and seed yield) and essential oil yield of fennel. GLC analysis revealed the significant increase in the components of essential oil, viz. trans-anethole (80.4–84.7 %), methyl chavicol (2.3–2.5 %) and fenchone (5.6–7.9 %). It was concluded that foliar spray of SA at 10−4 M might be employed for enhancing the plant growth as well as yield and quality of essential oil of fennel.