INTERACTIONS BETWEEN ARBUSCULAR MYCORRHIZAL FUNGI AND THE HEMIPARASITIC ANGIOSPERM RHINANTHUS MINOR DURING COINFECTION OF A HOST

The outcome of dual infection of the grass Lolium perenne L. by arbusc ular mycorrhizal (AM) fungi and the parasitic angiosperm Rhinanthus mi nor L. was investigated in a glasshouse study. Colonization oft, peren ne roots by AM fungi was significantly reduced by the presence of R. m inor, as was host growth which fell by 44-51%. It was concluded that t hese two responses were linked, with AM colonization declining in resp onse to the reduction in availability of host carbon. Parasite growth and reproductive output rose by 58% and 47% respectively when the host s were mycorrhizal. These trends were unrelated to the attachment succ ess of the parasite, but were accompanied by a significant increase in the formation of secondary haustoria. The benefits afforded the paras ite when the hosts were mycorrhizal were attributed to increased carbo n and nutrient flux resulting from alternations in sink strength. Host responses to parasitism and mycorrhizal colonization were not affecte d by the interaction between the two symbionts. However, the suggestio n is made that the interaction between the AM fungi and parasite might have long-term ecological implications for the host species via its i mpact on parasite fecundity.