BUDAPEST, Oct 18 (Reuters) - Hungary should strengthen ties with the European Union, put its economy on a path to adopting the euro currency and join the European Public Prosecutor"s Office to root out corruption, the opposition"s joint prime ministerial candidate told Reuters. Peter Marki-Zay, a political outsider with no party affiliation, will challenge Prime Minister Viktor Orban in an election next year after winning an opposition primary on Sunday. read more Marki-Zay will lead an alliance of six opposition parties against Orban. His comments to Reuters set him apart from Orban who, after over a decade in power, has strained relations with many EU leaders, particularly over democratic standards. "Hungary"s main priority should be a reorientation of its foreign policy, which is not merely a symbolic step," Marki-Zay said late on Sunday among jubilant supporters in a Budapest bistro where he announced his victory. Marki-Zay, a 49-year-old conservative, said Orban"s close ties with Russian President Vladimir Putin, China and Turkey were not in line with what he called European values. "For us, European values, European integration, democracy, the rule of law and a free market economy are extremely important values," he said. "The fight against corruption would be a part of this statement of values." The EU is at loggerheads with the nationalist government in Budapest over issues ranging from migration policy and LGBT rights to media freedoms. The row over democratic standards has contributed to a delay in payments to Hungary from the EU"s COVID-19 pandemic recovery fund. Opinion polls show Orban"s ruling Fidesz and the opposition alliance running neck-and-neck though they do not yet gauge the impact of Marki-Zay"s victory on Sunday. Mujtaba Rahman, Managing Director at the Eurasia Group think tank, said he now put the likelihood of Orban winning a simple majority at 55%, compared with 65% previously, and that the chances of an opposition alliance majority had risen from 20% to 40%. BATTLING CORRUPTION If the opposition alliance wins, Hungary should join the European Public Prosecutor"s Office (EPPO), Marki-Zay said. The EPPO has the authority to investigate fraud against the EU budget, as part of a clampdown on corruption. "Hungary must not veto steps aimed at deepening European integration," Marki-Zay said. "It is intolerable that a country can say no to joining the EPPO to shield its corrupt autocrats." Orban"s government has opted out of joining the EPPO, and said the decision was a question of sovereignty. Marki-Zay said Hungary should rebalance its economy to be able to adopt the euro though he added that a surge in inflation and the budget deficit because of pre-election spending meant this would be unlikely to happen during the next parliament. NL8N2R718P Hungary has no target date to adopt the euro. Marki-Zay said Hungary was unlikely to enter the ERM-2 mechanism, a mandatory stage for joining the euro, before 2026. He also said he would review flagship deals made under Orban with Russia and China, including a 12.5-billion-euro ($14.48-billion) contract to expand Hungary"s Paks nuclear power plant that was awarded to Russia"s Rosatom without a tender, and a high-speed rail link between Budapest and Belgrade. "We will have to see whether these deals serve Hungarian national interests," Marki-Zay said, adding that he did not oppose nuclear energy but saw a lack of competition in awarding the project. ($1 = 0.8630 euros)