Biology subjects

Hager, H. A.

Publications and source records attributed to Hager, H. A..

2 recordsLinked to original sources

bioRxiv2021

Allelopathic effects of Epichloë fungal endophytes: experiment and meta-analysis

Host-specific Epichloe spp.endophytic fungal symbionts of pooid grasses that produce herbivore-deterring alkaloids and alter the grass hosts metabolite and protein profiles. Early observations suggested that Epichloe may have negative allelopathic effects on neighbouring plant species, particularly Trifolium spp. clovers, but subsequent allelopathy tests produced variable results. We examined two hypotheses: (1) Epichloe strains differ in allelopathic effect, and (2) Epichloe allelopathy negatively affects other plant species. We performed a greenhouse experiment using root exudates from Lolium perenne L. hosting different E. festucae var. lolii (Latch, M.J. Chr. & Samuels) C.W. Bacon & Schardl strains to compare their allelopathic effects on native legumes and forbs. We then used meta-analysis to examine the evidence to date for allelopathic effects of Epichloe endophytes. We found little difference in effect among E. festucae var. lolii strains and very little evidence for negative allelopathic effects of Epichloe in cool-season grasses across a range of methodologies, target plant species, and response measures. Negative allelopathic effects were detected only for root hair measures, which were from a single study. Positive effects on biomass were found for some experimental subgroups, including legumes. However, the majority of response variables showed no evidence for Epichloe allelopathy. Although there is currently little evidence for negative Epichloe allelopathic effects, our meta-analysis identified several research gaps. Experiments testing the functional belowground effects of Epichloe presence may help to determine its effects on non-host plant performance via plant-soil feedbacks.

ecology↗

bioRxiv2021

Costs, Benefits, Parasites and Mutualists: The Use and Abuse of the Mutualism-Parasitism Continuum Concept for Epichloë Fungi

The species comprising the fungal endophyte genus Epichloe are symbionts of cool season grasses. About half the species in this genus are strictly vertically transmitted, and evolutionary theory suggests that these species must be mutualists. Nevertheless, Faeth and Sullivan (e.g. 2003) have argued that such vertically transmitted endophytes are "usually parasitic," and Muller and Krauss (2005) have argued that such vertically transmitted endophytes fall along a mutualism-parasitism continuum. These papers (and others) have caused confusion in the field. We used a systematic review to show that close to half of the published papers in this field incorrectly categorize the interaction. Here, we develop the argument that advantages and disadvantages are not the same things as mutualism and parasitism and that experimental evidence must be interpreted in the context of theory. We argue that, contra Faeth and Sullivan, it is highly unlikely that such strictly vertically transmitted endophytes can be parasites, and that, contra Muller and Krauss, it is inappropriate to apply the continuum concept to strictly vertically transmitted endophytes. We develop a mathematical model to support and illustrate our arguments. We use the model to clarify that parasitism requires some degree of horizontal transmission, and that while it is appropriate to use the continuum concept when referring to the genus as a whole, or to species that possess horizontal transmission, we argue that it is inappropriate to use the concept when referring to species that are strictly vertically transmitted.

ecology↗