Abstract
Summary Species of the necrotrophic fungal pathogen Fusarium that cause head blight and crown rot of cereals including wheat also infect a number of alternative host plants. This raises the prospect of more damaging pathogen strains originating and persisting as highly successful saprophytes on hosts other than wheat. The immediate impact on pathogenic (aggressiveness) and saprophytic (growth rate and fecundity) behaviour of six isolates with low, moderate or high initial aggressiveness was examined in two species of Fusarium after their passage through 10 alternative plant hosts. One passage through alternative hosts significantly reduced the pathogenic fitness of most isolates, but this change was not associated with a concomitant change in their overall saprophytic behaviour. The overall weak association between aggressiveness, fecundity and growth rate both before and after passage through the alternative hosts indicate that pathogenic and saprophytic fitness traits may be independently controlled in both Fusarium species. Thus, there was no trade‐off between pathogenic and saprophytic fitness in these necrotrophic plant pathogens.