Five onion (Allium cepa L.) varieties were crossed in a complete diallel fashion. The twenty five progenies generated from the crosses were evaluated over two onion growing seasons of 2004/2005 and 2005/2006 at Sokoto and T/Mafara, Nigeria. The treatments were laid out in a Randomised Complete Block Design (RCBD) and replicated three times at each location and in each season. The results of the determination of the minimum number of genes controlling the inheritance of resistance to purple blotch disease in onion in the four seasons and in the combined analysis across seasons and locations indicated a minimum of one gene controlling the inheritance of the character.

Keywords: Inheritance, purple blotch, disease, resistance, onions