A Thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg for the Degree of Doctor of Philosophy / Greening is a severe disease of citrus and is a major cause of crop loss in many parts of Africa and Asia.Numerous attempts have been made by various workers to isolate the aetiological agent of the disease and although reports claiming the successful culture of the organism have appeared, the isolations were never fully confirmed. ( Abbreviation abstract ) / AC2017