Asymmetric competition between a hemiparasitic plant and a cyst nematode on a shared host plant

Closely related parasites can compete for limited resources of a shared hos t. Wt extend prior work by examining the interactions of two parasites from different kingdoms. We conducted a greenhouse experiment to test for possi ble competition between a root hemiparasitic plant Rhinanthus serotinus (Sc honh.) Oborny and a plant parasitic cyst nematode (Heterodera trifolii Goff art) which share a common host plant, the red clover (Trifolium pratense L. ). Competition between these species was strongly asymmetric: the presence of nematodes reduced the biomass and flower production of the hemiparasitic plant by 74% and 81%, respectively. Lu fact, the performance of hemiparasi tes grown on nematode-infected hosts was about as poor as that of hemiparas ites grown without a host plant. In contrast, the presence of the hemiparas itic plant did not affect the population size ol number of cysts produced b y the parasitic nematodes. These results demonstrate competition between an animal parasite and a plant parasite for a shared host resource.