The flashpoint involving the two men followed a match that was pockmarked by red cards for Rangers players Steven Whittaker, Madjid Bougherra and El Hadji Diouf, 13 cautions and a series of angry scenes in the Celtic Park technical areas and tunnel.
The story of El Dorado is explored further in the Lost Kingdoms of South America, a series for BBC Four starting on Monday 14January at 21:00 GMT and the British Museum Digital Exhibition.
After a series of trials, they found one and the town of El Diviso, Colombia, where the research took place, has been selling seeds of this variety to neighbouring towns ever since.
Spanish police carried out a series of raids on offices, laboratories and flats in Madrid, Zaragoza and El Escorial in May 2006 as part of an investigation known as Operation Puerto.