HARARE (Reuters) - Zimbabwe s President Emmerson Mnangagwa told members of his ruling ZANU-PF party on Friday they would have to start fixing the economy if they wanted a chance of winning next year s vote. Mnangagwa spoke at a party congress that drew a line under the rule of ousted veteran leader Robert Mugabe by formally expelling his wife Grace and her allies from the organization and by endorsing Mnangagwa as party chief and candidate.  We will only win at the ballot box if we can show signs that we are reviving our economy and at the same time we will only be able to make economic gains if we can secure re-election,  he said. Zimbabwe s economy collapsed in the latter half of Mugabe s rule, especially after violent and chaotic seizures of thousands of white-owned commercial farms.     The southern African nation could hold elections as early as March, Mnangagwa said this week, which would be just five months after the de facto military coup which ended Mugabe s 37-year reign.  Democracy bids that as a political party, ZANU-PF must always compete for office through pitting itself against opposition parties in elections which must be credible, free, fair and transparent,  Mnangagwa, 75, told the congress in downtown Harare. British Foreign Secretary Boris Johnson said late last month that financial support for the new government to stabilize its currency system and help it clear World Bank and African Development Bank arrears depended on  democratic progress . In a sign of the military further consolidating its political power, Mnangagwa made three generals members of the party s Russian-styled executive Politburo, the supreme decision-making organ of ZANU-PF. Major General Engelbert Rugeje was appointed political commissar, a job focused on revamping party structures and preparing for elections. Mnangagwa said he would name two deputies in a few days. Defence Forces Commander General Constantino Chiwenga is a strong contender for one of the vice presidency slots as a reward for spearheading the de facto coup that ended Mugabe s rule. Mnangagwa, whose sacking as vice-president set off the chain of events that led to Mugabe s removal, said the ZANU-PF congress should define a new trajectory - which he did not spell out - and put behind it the victimization of members seen in the past. 