Brazil's environment minister, hailed as a champion of the green movement but scorned by powerful farming groups, resigned on Tuesday after losing key battles in her efforts to protect the Amazon rainforest. Marina Silva's resignation is likely to reinforce the view that President Luiz Inacio Lula da Silva is more concerned with economic development than conservation as a commodities export boom fuels Brazil's growth. It could also be a setback for Brazil's ambitions to become a major voice in global environmental debates.