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.