The share price of Switzerland-based agrochemical group Syngenta plunged almost 18 percent on Wednesday after American biotech giant Monsanto announced the withdrawal of its takeover bid.

The share price sank lummeted 17.8 percent to 311.50 Swiss francs ($329.10, 289.23 euros) just before 1500 GMT, as Switzerland's main SMI index fell by 2.1 percent.