BRUSSELS, Aug 22 (Reuters) - The European Commission said on Tuesday it had started an in-depth investigation of Bayer's BAYGn.DE planned $66 billion takeover of U.S. seeds group Monsanto MON.N , saying it was worried about competition in pesticide and seeds markets.

The deal between the two companies would create the world's largest integrated pesticides and seeds company, the Commission said, adding this limited the amount of competitors selling herbicides and vegetable seeds in Europe.

"The Commission has preliminary concerns that the proposed acquisition could reduce competition in a number of different markets resulting in higher prices, lower quality, less choice and less innovation," the European Commission said in a statement.

Bayer had previously submitted commitments aimed at easing the EU's antitrust concerns over the deal with Monsanto, but the company declined to say what was offered. urn:newsml:reuters.com:*:nL5N1KN4T1

If approved, the deal would be the third large tie-up in the agrochemicals sector but other companies also had to offer concessions to get regulators on board.

Dow DOW.N only secured regulatory clearance to acquire DuPont DD.N after pledging to sell key research and development activities and other major assets.

And ChemChina CNNCC.UL had to sell a large chunk of its subsidiary Adama's pesticide, herbicides and insecticides business, its seed treatment products for cereals and sugar beet and a substantial part of its plant growth regulator business for cereals to win EU approval to buy Syngenta SYNN.S .

(Reporting by Robert-Jan Bartunek, editing by Julia Fioretti) ((robertjan.bartunek@thomsonreuters.com; +32 2 2876850; Reuters Messaging: robert-jan.bartunek.thomsonreuters.com@reuters.net))

Keywords: MONSANTO M&A/BAYER EU