Infection of Holcus lanatus and H. mollis by Epichloë in Experimental Grasslands

Abstract

The infection of grasses by systemic fungal parasites in the genus Epichloe was documented in six experimental grassland sites at Silwood Park, Berkshire, UK. The potential of insect herbivory acting as a selective agent favouring infection was investigated by comparing insecticide-treated and control plots within sites. The sites were established at different times from the colonization of bare ground and represented a range of grassland types occurring in close proximity. Five of 11, common grasses were occasionally infected by Epichloe. Holcus lanatus and H. mollis were the most frequent hosts and infection occurred primarily in the three oldest sites. Disease levels and host density were quantified by counting all healthy and diseased inflorescences in replicatedone-m2 plots at each site. In two of the sites where H. lanatus was the primary host disease levels were three times higher in insecticide-treated vs control plots. Holcus mollis was the primary host in the other site although visible manifestations of disease were rare. However, microscopic examinations revealed that 69% of all samples were asymptomatically infected and that infections were significantly less frequent in insecticide-treated plots. While insect herbivory appears to favour infected H. mollis, disease incidence in H. lanatus was highest in insecticide-treated plots.