(Changes headline in July 15 story to reflect Lula extending lead over Flavio Bolsonaro)

SAO ‌PAULO, July 15 (Reuters) - Brazilian President Luiz Inacio ‌Lula da Silva has widened his lead over right-wing Senator ​Flavio Bolsonaro in the run-up to October's presidential election, a Quaest poll commissioned by brokerage Genial showed on Wednesday.

It is the first Quaest survey following a ‌series of political ⁠developments including a corruption investigation targeting a senior Lula ally and arguments about ⁠accountability over new U.S. tariff threats against Brazil.

• Leftist Lula is seen with 45% of voting intentions ​in a ​potential second-round runoff, compared ​with 37% for Senator ‌Bolsonaro, currently the main opposition hopeful.

• A Quaest poll in June showed Lula leading Flavio Bolsonaro by 44% to 38%.

• In a first-round scenario, Lula would take 40%, Bolsonaro 28%, Ronaldo Caiado 4%, Renan ‌Santos 3% and Romeu Zema ​2%.

• In Brazil, if no ​candidate gets more ​than 50% of valid votes, the ‌two frontrunners go to a ​second-round vote.

• ​Quaest surveyed 2,004 people between July 10 and 13. The poll has a margin of error ​of two ‌percentage points in either direction.

(Reporting by Michael Susin ​and Isabel Teles; Writing by Victoria Pacheco; ​Editing by Andrew Heavens)