Updated

Five allied political parties endorsed the presidential nominee of the bigger right-leaning Brazilian Social Democracy Party on Thursday, giving a boost to the man seen as the establishment candidate in Brazil's fractured political landscape.

The candidate, conservative former Sao Paulo Gov. Geraldo Alckmin, has been struggling to top 10 percent in opinion polls ahead of the October elections. But with the group's endorsement, he will get more free air time on TV and radio during the presidential campaign plus the support of more than 1,000 mayors nationwide.

The five parties make up the "Big Center" coalition in Congress, holding 164 of 513 seats in the Chamber of Deputies and 17 of 81 seats in the Senate. Many members of the five have been caught up in Brazil's sprawling "Car Wash" corruption investigation, which has jailed politicians and business executives across Latin America.

Leaders of the coalition said Alckmin's running mate will come from one of the five parties. His favorite for the role, textile business mogul Josue Gomes, refused it earlier Thursday.

Jailed former President Luiz Inacio Lula da Silva has been leading in the polls, but he is likely to be barred from running and substituted by another member of his left-leaning Workers' Party.

Far-right former military officer Jair Bolsonaro, environmentalist Marina Silva and left-leaning Ciro Gomes also lead Alckmin in the polls.

The Big Center group had earlier negotiated to endorse Gomes, but Alckmin prevailed after convincing leaders of the five parties that his candidacy is viable.

Political analyst Alberto Almeida, who has written several books on Brazilian elections, said Alckmin probably can thank unpopular President Michel Temer for the coalition's endorsement.

"It is clear that Temer wants Alckmin to win and carry on with his austerity measures. All those five parties also support Temer in Congress," Almeida said.

Almeida said the endorsement could help Alckmin in competing with Bolsonaro, who polls second now thanks to a hard-line rightist political base.

With no one expected to win the first round outright, the goal is to finish first or second and move on the expected runoff ballot Oct. 27.

"This agreement gives Alckmin a lot of free air time. Estimates now suggest the governor will have 60 free ads on TV daily against two of Bolsonaro's. That will play a role," Almeida said.

Alckmin ran for president in 2006, but lost to da Silva by big margins. He was governor of the wealthy Sao Paulo state until this March, when he had to resign to run for president.