BRASILIA (Reuters) - Right-wing Brazilian presidential candidate Jair Bolsonaro held on to his lead in early polling ahead of October elections, with leftist Ciro Gomes challenging the more moderate Marina Silva for second place, a survey showed on Monday.

FILE PHOTO: Brazilian Partido Social Liberal (PSL) presidential candidate and former military officer Jair Bolsonaro gestures during a military event in Sao Paulo, Brazil May 3, 2018. REUTERS/Nacho Doce/File photo

Excluding jailed former president Luiz Inacio Lula da Silva, who will likely be barred if he registers to run, the MDA poll showed 18.3 percent of voters backing Bolsonaro, 11.2 percent for environmentalist Marina Silva and 9.0 percent for Gomes. Lula easily led a version of the poll in which his name was included, with 32.4 percent of voters’ intentions.

In a previous MDA poll in March, Bolsonaro had 20.0 pct, Silva polled at 12.8 percent and Gomes had 8.1 percent. The survey has a margin of error of 2.2 percentage points.

With more than four months until election day on Oct. 7, the field without Lula remains wide open. Candidates are working to build party coalitions and win the attention of voters disenchanted with Brazil’s corruption-tainted political class.

That has put investors on edge, as uncertainty about the race adds to doubts that Brazil will follow through on fiscal reforms started by the unpopular President Michel Temer, who was rejected by 88 percent of voters in the poll.

One of the main candidates defending those reforms, two-time Sao Paulo Governor Geraldo Alckmin, slipped from third to fourth place, behind Gomes, polling only 5.3 percent compared to 8.6 percent in March.

Brazil’s currency, the real, slipped 0.6 percent on the MDA poll to its weakest in two years, which traders attributed to the weak showing by Alckmin and stronger polling for Gomes, a critic of the government’s reform agenda.

Bolsonaro, a former army captain, is running on a tough law and order platform advocating looser gun controls, which has won him widespread support among Brazil’s agriculture sector. His voting on economic issues has been mixed and he has little legislative track record to show he can pass major reforms.

In a second-round runoff between Bolsonaro and Marina Silva, required if no candidate wins a majority in the first vote, the two long-time federal lawmakers are tied with 27.2 percent each.

Of those polled, 56.5 percent said they would never vote for Marina Silva and 52.8 refused to back Bolsonaro, rates that have risen since March.

The poll commissioned by transportation lobby CNT surveyed 2,002 people across Brazil from May 9 to 13.