- Opposition candidate is relative of south's Garang
* Turabi prefers to stay party head, will not stand
KHARTOUM, Jan 3 (Reuters) - The opposition Popular Congress Party has nominated a southern Sudanese as its presidential candidate for the first multi-party elections in 24 years in April, a move it says will promote national unity.
"The candidate is Abdullah Deng Nhial from the south," the party's top defence and security official, Mohamed al-Amin Khalifa, told Reuters on Sunday. "He is a relative of (late vice president) John Garang."
Garang was the charismatic leader of the former southern rebel Sudan People's Liberation Movement (SPLM) which fought a civil war lasting more than two decades with the north, ending in 2005.
His peace deal with President Omar Hassan al-Bashir's National Congress Party provided for north and south to share wealth and power, for national democratic elections in April 2010 and a southern referendum in 2011 on independence.
"This nomination can be a symbol of unity for Sudan because we are not separatists at all, and there is no racial discrimination within our party as within Islam itself," Khalifa added. Nhial is a Muslim and deputy head of the PCP.
The PCP leader, Islamist Hassan al-Turabi, will not stand for president because he prefers to remain head of the party, whose policy is that one person should not hold both posts, Khalifa said.
Turabi, once close to Bashir, left government and formed his opposition party after a bitter leadership battle with Bashir in 1999/2000.
Turabi won notoriety for his links to al Qaeda leader Osama bin Laden during bin Laden's stay in Sudan, Africa's largest country, in the 1990s.
Garang died in a helicopter crash just three weeks after being sworn in as Sudanese vice president. His death sparked riots in Khartoum in which dozens were killed, widening the north-south rift.
Most analysts agree the southerners are likely to vote for secession in 2011, though this means Khartoum would lose control of most of the country's proven oil reserves. The referendum is one of the most divisive issues on Sudan's political calendar.
Opposition parties have accused Bashir's NCP of vote buying, fraud and intimidation during voter registration which ended last month. The NCP denies fraud.
As well as the presidential election, Sudanese will vote for national and state parliaments and state governors in April. (Reporting by Opheera McDoom, editing by Tim Pearce)