Syngenta’s (SYNN.VX) chairman said any takeover offer needed to be at a fair price and provide a high degree of certainty that it will clear regulatory hurdles, as he reaffirmed the Swiss firm’s opposition to Monsanto’s (MON.N) current proposal. Basel-based Syngenta, the world’s largest maker of crop chemicals, rebuffed an initial approach by Monsanto in May partly on the grounds it did not address regulatory concerns. The U.S. firm then offered to pay Syngenta $2 billion if the merger failed to get approval from regulators, but this was rejected as “wholly inadequate”.