Part of the first author’s Ph.D. thesis. PROBIOL, UNCuyo, Argentina. ABSTRACT Fusarium basal rot (FBR), which is caused predominantly by Fusarium oxysporum and F. proliferatum, is the main limiting factor of onion crops. Resistant cultivars obtained in other countries do not behave as such in Argentina crop fields. The cultivars AntárticaINTA, Grano de Oro-Seminis, Valcatorce-INTA and TW-2007 (...