Fennel

Bitter fennel (Foeniculum vulgare Mill., subsp. vulgare, var. vulgare) is cultivated worldwide. It is one of the most important medicinal plants in Germany and has great economic significance. Bitter fennel is a hardy biennial or perennial herbaceous plant with yellow flowers and pinnate leaves. It is used to treat digestive issues and inflammation of the mucous membranes in the upper respiratory tract. Its medicinal effects are largely due to the essential oil extracted from the fruits, which has antispasmodic, secretolytic, secretomotor, and anti-inflammatory properties. The dried fruits are traditionally prepared as tea. They are also used to make dry extracts for coated tablets, alcoholic extracts for drops, and fennel oil for lozenges.

The essential oil's main constituents are trans-anethol (50–70%), fenchone (12–25%), and estragole (2–8%). Anethol, which tastes sweet, is considered antispasmodic and aids digestion. Together with fenchone, anethol is believed to be responsible for fennel fruits' expectorant effect. The European Pharmacopoeia defines bitter fennel (Foeniculi amari fructus) as having a minimum essential oil content of 4%, at least 60% of which is anethole, and at least 15% of which is fenchone.

Unwanted ingredient estragol: Reduction/minimization as a key breeding goal

Estragol, a natural component of fennel essential oil, has been the subject of scientific and regulatory discussions regarding its health effects for years. Due to potential health risks, the European Medicines Agency (EMA) and the European Food Safety Authority (EFSA) recommend limiting estragol intake, especially for children and for long-term use. Therefore, reducing undesirable estragol levels while preserving pharmacologically valuable compounds is a key goal of fennel breeding.

At Fraunhofer IME, we are investigating the genetic basis of estragol biosynthesis and developing new breeding strategies for low- or no-estragol fennel varieties. One challenge is that previous approaches to reducing estragol content have often resulted in a simultaneous decrease of the valuable compound trans-anethol. Developing fennel varieties with low estragol content and high pharmaceutical quality is the focus of our research and development efforts.

Unraveling the genetic basis of estragol biosynthesis

We have established tissue cultures and efficient transformation methods, laying the groundwork for the functional genome analysis of fennel. In addition, we have identified the first genes involved in estragol and trans-anethol biosynthesis. Using molecular markers, metabolic engineering, and genome editing, we are investigating their function and developing low-estragol varieties of fennel with optimized chemical profiles. These technologies can also be applied to other medicinal and aromatic plants containing estragol.