By Hans-Edzard Busemann ESSEN, Germany (Reuters) - The founder of the eurosceptic Alternative for Germany (AfD) appealed to colleagues on Saturday to end a bitter leadership dispute that threatens to rip apart the two-year-old party. The infighting has hit the ratings of the AfD and left it floundering at a time when it could have capitalised on anger over Greece's debt crisis. The acrimonious feud between founder Bernd Lucke, who wants to focus on liberal economic policies, and co-leader Frauke Petry who has won support from right-wing conservatives by homing in on immigration fears, has overshadowed campaigning.