A new poll shows the leading rival to Brazil's President Dilma Rousseff would defeat her in a second-round runoff vote in October's election.

The poll was published Tuesday on the Estado de S. Paulo's website. It was conducted by the respected Ibope firm.

It says 45 percent of respondents would vote for former environment minister Marina Silva in an expected second-round, compared to 36 percent for Rousseff.

Silva was the vice presidential candidate with Eduardo Campos.

But Campos died when his campaign plane crashed this month. Silva announced last week that she's filling his spot on the Brazilian Socialist Party ticket.

Silva and Rousseff meet later Tuesday for the first presidential campaign debate.

Ibope interviewed 2,506 voters this week. The poll has a margin of error of 2 percentage points.