BRASILIA/SAO PAULO (Reuters) - Brazil’s presidential election is up for grabs, according to a new poll, with popular ex-president Luiz Inacio Lula da Silva likely to be barred because of his corruption conviction and one-third of an electorate disenchanted by graft scandals saying they would not vote for any candidate.

Former Brazilian president Luiz Inacio Lula da Silva speaks during a meeting with members of the Workers Party (PT) in Sao Paulo, Brazil, January 25, 2018. REUTERS/Leonardo Benassatto

If he is allowed to run, Lula would lead the field with 34 percent of the vote in a scenario involving the most likely candidates, according to a Datafolha poll published Wednesday.

It was the first survey taken since Lula’s conviction on corruption charges was upheld by an appeals court last week.

The ruling will likely block him from the Oct. 7 election because of a law banning candidates convicted of crimes, though Lula is appealing.

Brazil’s establishment has been shaken by an unprecedented series of corruption investigations that began in early 2014 and focus on kickbacks at state-run firms. Over 100 powerful businessmen and politicians have been convicted, while dozens of congressmen, members of the executive branch and others remain under investigation.

The new survey showed Lula would be comfortably ahead of other candidates in the first round if he can run, with right-wing congressman Jair Bolsonaro trailing with 16 percent, followed by environmentalist Marina Silva at 8 percent.

The poll also indicated Lula would beat all other likely candidates in a second-round runoff, required if no single candidate wins a majority in the first round.

NO LULA

If Lula cannot run, Bolsonaro would take the lead but not get enough votes to win outright in the first round, according to the poll published by the Folha de S.Paulo newspaper.

Bolsonaro would lose in a runoff to two-time presidential hopeful Marina Silva, or face a dead heat with likely center-right candidate Geraldo Alckmin, the governor of Sao Paulo state.

If Lula is definitively disqualified by higher courts, a record 32 percent of Brazilians polled by Datafolha said they would vote for no one in the presidential race, an increase of 10 percentage points from a poll taken prior to his conviction.

That level of disenchantment with Brazil’s scandal-plagued political class is unprecedented, according to Datafolha director Mauro Paulino. The proportion of voters who said they would back no one in February 2014, ahead of the last election won by impeached leftist Dilma Rousseff, was 19 percent.

NO TRANSFER

If Lula is out of the running, Bolsonaro would get 18 percent in the first round while Marina Silva would get 13 percent and Ciro Gomes, the leftist former governor of Ceará state, 10 percent. TV presenter Luciano Huck and Alckmin would each get 8 percent without Lula.

The bad news for Lula’s Workers Party is that his ability to transfer votes is slim, with 15 percent of supporters saying they would back Marina Silva and 14 percent going for Gomes.

Datafolha found that 53 percent would never vote for a candidate backed by Lula.

In such an open field, the candidate best able to forge a coalition stands the best chance to take the lead.

That could favor centrist Alckmin, according to political scientist Lucas de Aragão, a partner at Brasilia consultancy Arko Advice.

Even though Bolsonaro and Marina Silva have better numbers, both have immense difficulties building coalitions and Bolsonaro appears to have hit his ceiling at 20 percent, he said.

“Alckmin’s strength is his potential to build a broad coalition. He might be starting the race from the back, but his car is much better than the others,” Aragão said.

The Datafolha interviews were conducted on Jan. 29-30, a few days after three appellate court judges voted to uphold Lula’s convictions on taking bribes and money laundering.

Lula, Brazil’s first working-class leader, held office from 2003 to 2010. He remains free pending appeals.

Datafolha interviewed 2,826 people across Brazil. The margin of error is 2 percentage points.