In a field experiment with a susceptible population of annual
wild carrot (Daucus carota) from Iran, artificial inoculations with
the fungal pathogen A. dauci led to a strong and very significant increase
of the diseased leaf area. The pathogen caused a very significant decrease
in fecundity and seed survival of the host. This considerable fitness
reduction by A. dauci would suggest that introgression of disease resistance
from cultivated (transgenic) carrot cultivars into wild carrot populations
could strongly increase the fitness of wild carrot. In spite of the potential
ability of A. dauci to lower the fitness of the host considerably, wild carrot
is very common in The Netherlands. Disease levels of wild carrot were estimated
in 26 natural populations in 1998. No A. dauci could be detected on the leaves,
and only 0.4% of the seeds were contaminated with A. dauci, in spite of the
conducive weather for A. dauci. Resistance tests showed that all 26 monitored
populations were highly resistant to A. dauci strains from The Netherlands.
It is probable that the strong potential fitness reduction by A. dauci led to
a high selection pressure towards resistance in The Netherlands. In conclusion,
our results suggest that transgenic resistance to A. dauci would not be beneficial
to wild carrot populations in The Netherlands because they are already resistant
to this pathogen.