Brazil corruption: President loses fourth minister
Brazil's Agriculture Minister Wagner Rossi has resigned amid a corruption scandal.
He is the third minister to leave office because of corruption allegations since President Dilma Rousseff came to power in January.
Mr Rossi said he had spent a month battling what he called "false accusations", and had had enough.
He is a member of the Democratic Movement Party of Brazil (PMDB), the president's largest ally in Congress.
"Over the last 30 days, I have faced a daily barrage of false accusations without any proof," Mr Rossi wrote in a letter cited by Agencia Brasil.
He had been accused of accepting bribes and free air travel from agricultural companies, local media report.
Relations between the president and the PMDB have worsened, with the party leader in the lower house of Congress, Henrique Eduardo Alves, speaking of "protests ... until Congress gets the respect we want".
Transport Minister Alfredo Nascimento and President Rousseff's chief of staff, Antonio Palocci, have also resigned since she took office.
Defence Minsiter Nelson Jobim quit, after allegedly making disparaging remarks to the media about colleagues.