The deal, announced in February 2016, was prompted by China's desire to use Syngenta's portfolio of top-tier chemicals and patent-protected seeds to improve domestic agricultural output. It is China's biggest foreign takeover to date.
It is one of several deals that are remaking the international market for agricultural chemicals, seeds and fertilizers.
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The trend toward market consolidation has triggered fears among farmers that the pipeline for new herbicides and pesticides might slow. Regulators have required some divestments as a condition for approving the acquisition.
Based on preliminary numbers, around 80.7% of Syngenta shares have been tendered, above the minimum threshold of 67% support, the partners said in a joint statement.
The agreed offer is for $465 per share. Syngenta shares closed on Thursday at 459 Swiss francs ($465.14).
Syngenta sells its products in more than 90 countries under such brand names as Acuron, Axial, Beacon and Callisto. It sells seeds such as cereals, corn, rice, soybeans, and vegetables.