Can yeast extract and chitosan-oligosaccharide improve fruit yield and modify the pharmaceutical active ingredients of organic fennel?

Abstract

Fennel is one of the most significant medicinal and aromatic herbs. It is used as a culinary ingredient and has an essential role as a raw material in the pharmaceutical industry. Many researchers across the world are working to increase the active components in the essential oil of medicinal and aromatic plants under organic farming. Growth promoters are one of the most effective methods for stimulating secondary metabolite production under organic agriculture. The objectives of this study were to investigate how foliar sprays of yeast extract (Y) and/or chitosan-oligosaccharide (CHO) affected the growth and yield of organic fennel (Foeniculum vulgare spp. vulgare Mill.) and if these applications can stimulate the production of pharmaceutical active ingredients in fennel fruits. Fennel foliage was subjected to foliar spray of Y at concentrations of 0 (Y0), 2 (Y1), and 4 (Y2) g L−1, and CHO at concentrations of 0 (CHO0), 60 (CHO1), and 120 (CHO2) mg L−1 twice. The results revealed that both Y and CHO treatments promoted growth parameters and leaf pigments content. Total phenols and nutritional content (N, P, K, Ca, and Mg) in fennel fruits were also improved. Furthermore, Y and CHO treatments enhanced fruit and oil productivity. Foliar spraying with Y and/or CHO, as well as their combination, resulted in significant modification in main pharmacological active components in fennel essential oil. Treated plants with Y1 had the lowest proportion of estragole (24.61 %), an undesirable component in fennel oil, and the highest concentration of anethole (64.50 %), which improved the oil quality. While treated plants with CHO1 or CHO2 displayed an increase in estragole content by about 33.34 and 46.59 % compared with Y1-plants, respectively.These new findings demonstrated that applying Y2 or CHO at both levels not only increased fennel growth and yield, but also contributed to increasing estragole and decreasing anethole concentration, and both had a negative impact on essential oil quality. However, applying Y1 enhanced fennel productivity as well as essential oil quality.