Vertically transmitted fungal endophytes: different responses of host‐parasite systems to environmental conditions

Abstract

The relationship between vertically transmitted asexual fungal grass endophytes and their hosts is considered to be mutualistic. Results from agronomic field support this line of reasoning but recent studies have shown more variable results in natural systems. We investigated how high and low nutrient and water treatments affected biomass allocation patterns of endophyte‐infected and uninfected Festuca pratensis and F. rubra in greenhouse experiments over two growing seasons. Irrespective of infection status, both grass species showed improved performance on highly fertilized and watered soils. However, infected F. pratensis plants produced larger tillers than endophyte‐free plants on soil low in nutrients and water in the first growing season, although they (E+) otherwise showed decreased performance on nutrient‐poor soil. In low nutrient and water conditions, endophyte‐infected plants produced less tillers and had lower total biomass compared to uninfected plants, and displayed a negative phenotypic correlation between seed production and vegetative growth. The latter indicates costs of reproduction when the plant shares common resources with the fungal endophyte. However, endophyte infection status (E+, E−) interacted significantly with the soil fertilisation in terms of plant growth, having a stronger positive effect on growth in infected F. pratensis plants. In F. rubra, endophyte‐infected plants showed higher vegetative growth in fertilized and watered soils compared to uninfected plants. However, infected plants tended to produce fewer inflorescences. This had no effect on seed production, perhaps because seed production was partly replaced by asexual pseudovivipary. Contrary to the general assumption in the literature that fungal endophytes are plant mutualists, these findings suggest that the costs of endophytes may outweigh their benefits in resource limited conditions. However, the costs of endophyte infections appear to differ among the grass species studied; costs of endophytes were mainly detected in F. pratensis under low nutrient conditions. We propose that differences in response to endophyte infection in these species may depend on the differences in life‐history strategies and environmental requirements of these two fescue and fungal species and may change during the life span of the plant.

Inherited fungal symbionts enhance establishment of an invasive annual grass across successional habitats

“…Faeth et al 2004). Further, evidence shows that endophyte eVects on a given host species may shift from mutualistic to antagonistic depending on environmental context (Cheplick et al 2000;Ahlholm et al 2002;Cheplick and Faeth 2009).…”

Environmental conditions and host plant origin override endophyte effects on invertebrate communities

“…Because alkaloids are nutrient-rich compounds, their synthesis has cost to other basic plant growth and reproductive functions Faeth and Bultman 2002;Faeth and Fagan 2002). These costs may outweigh the benefits of the endophyte infection in most environments, but particularly so in nutrient-poor environments in nature (Ahlholm et al 2002;Lehtonen et al 2005). Thus, in its native habitat, infected wild tall fescue may produce lower levels and fewer types of alkaloids than its cultivated and selective-bred varieties in nutrient-rich environments in the introduced range (Saikkonen et al 1998Siegel and Bush 1996; but see Piano et al 2005).…”

Effect of Endophyte Association with Brachiaria Species on Shoot and Root Morpho-physiological Responses under Drought Stress

“…Variable effects of endophytes are related to high dependence of host-endophyte associations on environmental conditions and genetics of both host and endophyte [21][22][23][24]. In the present study, significant three-way and two-way interactions influenced several traits, including leaf area, total root diameter, diameter of cortex, area of stele, number of tillers, shoot elongation, stomatal conductance, shoot biomass, and diameter of xylem vessels (p<0.05).…”

“…In contrast, Cheplick [35] found less number of tillers, leaf area and biomass in some endophyte-infected genotypes of perennial ryegrass than in endophyte-free plants under both irrigated and drought conditions. Decrease in leaf area due to endophyte infection in some cultivars could be ascribed to either resource allocation to tiller base and root or to endophyte metabolic use of photosynthates supplied by the host [21,[36][37][38].…”