XVI International Botanical Congess

If parasites decrease the fitness of their hosts significantly,selection for resistance would be expected.We grew host plants originating from previously parasitised or unparasitised populations with or without the parasite to study the effects of the infection,and the performance of the parasite on the two host types.The parasite significantly decreased the total biomass and reproduction of the host.There were no differences between the two host types in the effects of the parasite. However, parasites grown with hosts from previously parasitised populations had lower biomass and produced less flowers than parasites grown with hosts from previously unparasitised populations.These results suggest that parasitism has selected for resistance,as indicated by the decreased performance of the parasite.