Dar es Salaam - Tanzania's four main opposition parties chose ex-prime minister Edward Lowassa as a joint presidential candidate on Tuesday, three months ahead of a general election scheduled for October 25.Lowassa, 61, was the east African country's prime minister between 2005 and 2008, when he resigned over corruption allegations, charges he denied.He defected last week from the ruling Chama Cha Mapinduzi (CCM) party to join the opposition Chadema party.He will run for the top post for Chadema, as well as the Civic United Front (CUF), NCCR-Mageuzi and the National League for Democracy (NLD).Lowassa had joined the race earlier this month to run as the CCM's presidential candidate, where he was seen as a frontrunner among 42 candidates, but lost out to government minister John Magufuli.Following his defeat, Lowassa claimed the ruling party was "infested with leaders who are dictators, undemocratic and surrounded with greedy power mongers."The ruling CCM party has dominated politics since modern Tanzania was formed in 1964, and currently has two-thirds of seats in parliament.The four parties will also field joint candidates for parliamentary and council seats."Ours is the coalition of victory. We are out to take over from CCM," Chadema national chair Freeman Mbowe told a meeting of the party."Our party's central committee nominated Lowassa to run for president last week, and the decision was endorsed by the national congress."Juma Duni Haji, resigned as a minister for infrastructure development in the semi-autonomous Zanzibar government, was named as his running mate.President Jakaya Kikwete cannot stand again after serving the two term limit.