Site- and species-specific differences in endophyte occurrence in two herbaceous plants

1 Endophyte fungi exist within the living tissues of all plants, but compared to grasses and trees, remarkably little is known about their ecology in herbaceous species. These fungi produce an array of metabolites in culture and there is some evidence that they can increase the resistance of plants to herbivorous insects. 2 As herbaceous plant endophytes are thought to be unspecialized, ubiquitous taxa, we hypothesized that their occurrence within two closely-related plant species would not vary between local plant communities. Furthermore, we expected to find negative relations between endophyte occurrence and that of a herbivorous insect. 3 We tested these hypotheses by isolating endophytes from Leucanthemum vulgare and Cirsium arvense (Asteraceae) plants growing together in five populations, each about 13 km apart. Damage by the leaf mining fly, Chromatomyia syngenesiae was also measured on each plant. 4 C. arvense harboured more species of fungi per plant and the number of isolates recovered per leaf was also higher. Several fungi showed differences in occurrence within the two plants, but these differences were not consistent between sites. The similarity in the endophyte assemblage decreased with increasing inter-site distance in C. arvense, but not in L. vulgare. We conclude that endophytes either colonize C. arvense more readily or have greater activity within this host (or both). 5 Leaf miner attack was positively related to total endophyte species number in L. vulgare, but not so in C. arvense, while occurrence of Chaetomium species was negatively associated with insect attack in both plants. In L. vulgare, only 5% of relations between occurrence of different endophyte species were significant, but in C. arvense, this figure was 43% and all were negative. 6 This study has important implications for understanding the factors that influence plant resistance to insects. It is the first report of endophytic fungi affecting host plant choice by insects in herbaceous plants. The abundance of unspecialized endophytes in forbs means that they are a neglected, but important aspect of plant-herbivore relations