JOHANNESBURG, Sept 21 (Reuters) - Takatso Consortium said on Wednesday it was still in discussions with South Africa’s Treasury over its purchase of a 51% stake in the country’s struggling national airline but said both parties were committed to an agreement. The transaction was large and complex and so might take time to finalise, it said in an emailed statement, although it said a due diligence process was largely complete and had identified no material issues.