Popular environmentalist Marina Silva looks capable of winning Brazil's presidential election in October but a major campaign gaffe and mounting attacks from other candidates and the media suggest the race is still wide open.

Polls have shown Silva with a lead of about 10 percentage points over President Dilma Rousseff if the Oct. 5 election goes to a runoff, as seems likely.

Silva's meteoric rise has led Brazilian stocks to rally 10 percent in the last three weeks on hopes she would be more business-friendly than Rousseff and help stir a stagnant economy.