BOGOTA (Reuters) - A significant lead in votes for Colombian right-wing candidate Ivan Duque over leftist Gustavo Petro in presidential primaries pushed the peso up against the dollar on Monday as investors bet Duque would be more business friendly that the former guerrilla candidate.

REFILE - CORRECTING GRAMMAR Ivan Duque, presidential candidate of the party Centro Democratico, gives a speech after finding out the results of the legislative election in Bogota, Colombia March 11, 2018. REUTERS/Carlos Julio Martinez

Petro’s promise of a “social economy” that would raise taxes and shift away from oil, Colombia’s top export, toward agriculture has worried investors in the Andean nation as opinion polls showed the former member of the disbanded M-19 guerrilla group and ex-mayor of Bogota running ahead of Duque.

Parties will likely now look to form alliances before the May 27 election to replace President Juan Manuel Santos. If no candidate gets more than 50 percent of the vote, a second round will be held in June.

Sunday’s primaries - in which Duque won almost 42 percent more votes than Petro did - were considered a better test of voter support than often inaccurate opinion polls, although some voters will have participated strategically and may not back either winner in the presidential vote.

More than 6 million votes were cast in the three-way right-wing primary and 3.5 million in the two-way left-wing contest.

While all candidates advocate clamping down on corruption and investment in education and health, the two top pollers differ in their views on a peace deal with Marxist FARC rebels.

Duque, 41, supported by former President Alvaro Uribe and his Democratic Center party, backs foreign investment and an aggressive security strategy meant to combat Colombia’s remaining rebel group, which regularly kidnaps and bombs oil pipelines.

He has been vocal in his opposition to the 2016 FARC accord, which could stymie implementation if he wins.

Petro, 57, and his Colombia Humana party pledges to improve conditions for the poor, ban open pit mining and use clean energy.

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Voters also elected a new congress. While no party came close to winning control of either legislature, the Democratic Center party came out on top in the Senate, with 19 seats and second in the lower house, with 32 seats.

Petro’s Decencia coalition won just four Senate seats, and only two seats in the lower house.

“There’s now sure to be at the presidential level a shake out of candidates over the coming weeks as we approach the first round – Petro can’t yet be completely discounted but he looks further from his goal today compared with Friday,” said Rupert Stebbings, managing director of equities at Grupo Bancolombia.

The peso <COP = STFX> strengthened 0.67 percent against the dollar to 2,851 and local Treasury bonds rose to yield 6.238 percent from Friday’s close of 6.278 percent.

The peso and bonds markets are much more liquid than the stock market, which is heavily dependent on oil prices and shares of state-owned oil company Ecopetrol.

“The fact that the center right has won - that doesn’t represent a political change for the markets,” said Juan David Ballen, head of economic studies at Casa de Bolsa brokerage.

The FARC, now the Revolutionary Alternative Common Force party, were guaranteed five seats in both houses as part of the peace deal and failed to win any others.

Also running for president are Sergio Fajardo, a former mayor of Medellin, and ex-vice president German Vargas Lleras.

They both favor improvements to infrastructure and tax cuts for businesses, though Fajardo is considered left-leaning.

Duque and Vargas Lleras, from the Radical Change party, have strong party machines behind them and can count on backing in Congress if they win.

Other candidates include Liberal party elder statesman Humberto de la Calle, who lead government negotiators at FARC talks, and former defense minister and U.S. ambassador Juan Carlos Pinzon.