Endophytes influence protection and growth of an invasive plant

Abstract

We investigated the symbiotic activities of fungal endophytes isolated from spotted knapweed, Centaurea stoebe. Previously, an analysis of community similarity had demonstrated differences in the endophyte communities of C. stoebe in its native and invaded ranges. Here, we found that specific endophytes can exert positive effects on their host, whereas others exert negative effects. Endophytes produced metabolites that inhibited germination of a competitor of C. stoebe. Endophytes also repelled a specialist insect herbivore, perhaps by producing biologically active volatiles. Yet other endophytes acted as cryptic pathogens of C. stoebe, suppressing its germination, reducing its growth, increasing the abundance of a generalist insect herbivore, and delaying or suppressing its flowering. Since, as reported here, endophytes are not functionally interchangeable, previously reported community differences could be contributing to the invasiveness of C. stoebe.

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Acknowledgements

R. Menjivar's participation in the project was supported by the Norman E. Borlaug International Agricultural Science and Technology Fellows Program

Figures and Tables

Figure 1 Results of 6 dual-choice experiments to determine the settling behavior of Larinus minutus on individual flowerheads or artificial flowers of spotted knapweed with and without inoculation by endophytes. Bars show the relative proportion of observations of weevils on the two treatments being compared over a 2-hour period. Asterisks indicate whether the results depart from equal proportions on each treatment (χ², p = 0.05).

Figure 2 Growth, flowering and biotic interactions of C. stoebe, all significantly influenced by specific endophytes. Endophyte genera are followed by CID numbers that are keyed to GenBank accession numbers and to isolation frequencies in the native and invaded ranges of C. stoebe.1

Table 1 A summary of experiments

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