Endophyte Infection Frequency Research Articles

Neotyphodiumendophyte infection frequency in annual grass populations: relative importance of mutualism and transmission efficiency

Persistence and ubiquity of vertically transmitted Neotyphodium endophytes in grass populations is puzzling because infected plants do not consistently exhibit increased fitness. Using an annual grass population model, we show that the problems for matching endophyte infection and mutualism are likely to arise from difficulties in detecting small mutualistic effects, variability in endophyte transmission efficiency and an apparent prevalence of non-equilibrium in the dynamics of infection. Although endophytes would ultimately persist only if the infection confers some fitness increase to the host plants, such an increase can be very small, as long as the transmission efficiency is sufficiently high. In addition, imperfect transmission limits effectively the equilibrium infection level if the infected plants exhibit small or large reproductive advantage. Under frequent natural conditions, the equilibrium infection level is very sensitive to small changes in transmission efficiency and host reproductive advantage, while convergence to such an equilibrium is slow. As a consequence, seed immigration and environmental fluctuation are likely to keep local infection levels away from equilibrium. Transient dynamics analysis suggests that, when driven by environmental fluctuation, infection frequency increases would often be larger than decreases. By contrast, when due to immigration, overrepresentation of infected individuals tends to vanish faster than equivalent overrepresentation of non-infected individuals.

Variation in the abundance of fungal endophytes in fescue grasses along altitudinal and grazing gradients

Epichloë festucae, a common fungal symbiont of the genus Festuca (family Poaceae), can provide its host plant with protection against herbivores. However, infection might also be associated with a cost to its host plant. We examined the distribution of Epichloë festucae infection in natural populations of three fescue grasses, Festuca rubra, F. ovina and F. vivipara, on mountains in northern Sweden to determine whether infection frequency varied with reindeer Rangifertarandus grazing pressure and altitude. Two differently‐scaled approaches were used: 1) infection frequency was measured at a local scale along ten elevational transects within a ca 400 km2 area and 2) infection frequency was measured on a regional scale along elevational transects on 17 mountains classified as having a history of high or low reindeer grazing pressure. Mean infection frequencies in F. rubra were 10% (vegetative tillers at a local scale), and 23% (flowering culms at a regional scale), and in F. ovina they were 13% (local scale) and 15% (regional scale). Endophyte infection frequency in F. vivipara, was, on average, 12% (local scale) and 37% (regional scale). In F. rubra, infection decreased significantly with increasing altitude at both the local and regional scale, and was positively correlated with grazing pressure. In F. ovina, an opposite trend was found at the regional scale: infection frequency increased significantly with increasing altitude, while no discernible distribution pattern was observed at the local scale. No elevational trends were observed in infection of F. vivipara. These patterns in the distribution of endophyte‐infected grasses in non‐agricultural ecosystems may be explained by both biotic (grazing) and abiotic factors (altitude). Differences in ecology and life history of the studied grass species may also be of importance for the different results observed among species.

Differential expression of loline alkaloids in perennial ryegrass infected with endophyte isolated from tall fescue

Twenty half-sibling families of perennial ryegrass inoculated with a strain of endophyte isolated from tall fescue were analysed for loline concentrations. Inoculation success varied between families. Frequency of loline expression of different families varied moderately. Family effect on loline concentrations was significant. In another set of material, derived from plants exposed to field selection, endophyte infection frequency in seed harvested from plants verified as infected was close to 100%. Loline concentrations varied significantly between families. For nine of 23 families, none of the three plants sampled showed any measurable loline. As in other data sets, the results show variation in concentrations of endophyte alkaloids controlled by the genetics of the host plant. Keywords: Neotyphodium, host variation, adaptation, symbiosis, lolines

Ecological importance of Neotyphodium spp. grass endophytes in agroecosystems

Abstract Neotyphodium spp. fungal endophytes form symbiotic associations with agronomic grasses with expression ranging from mutualistic to parasitic. In general, endophyte infection frequencies seem more variable in natural compared to pastoral situations, suggesting that expression and benefits attributable to endophyte infection depend on the resource environment in which the host–endophyte complex was formed and the conditions under which it is being grown. Emerging evidence suggests that expression is not always mutualistic or beneficial to the host in terms of productivity and persistence in resource‐limited environments. Expression of host–endophyte associations will vary depending on resource availability and environmental conditions that influence host physiology and growth, and herbivore behavior. New research suggest alkaloids and secondary metabolites produced by host–endophyte associations can have physiological functions in addition to acting as herbivore deterrents. Novel host–endophyte associations are being created that maintain insect and disease resistance, while having minimal detrimental impact on mammalian herbivores. The influence of host–endophyte associations on sward composition and soil food webs is only now coming to light. While novel endophyte associations and their attendant mechanisms can be considered beneficial in some respect, the associations may not be as adaptable to stressful or marginal resource environments and could have long‐term ecological impacts measured in terms of persistence and total productivity of the sward. We review the extensive published work on host–endophyte interactions and illustrate the complexity of host–endophyte associations and their interactions with environment, and the range of responses that occur.

Herbivores cause a rapid increase in hereditary symbiosis and alter plant community composition.

Microbial symbioses are ubiquitous in nature. Hereditary symbionts warrant particular attention because of their direct effects on the evolutionary potential of their hosts. In plants, hereditary fungal endophytes can increase the competitive ability, drought tolerance, and herbivore resistance of their host, although it is unclear whether or how these ecological benefits may alter the dynamics of the endophyte symbiosis over time. Here, we demonstrate that herbivores alter the dynamics of a hereditary symbiont under field conditions. Also, we show that changes in symbiont frequency were accompanied by shifts in the overall structure of the plant community. Replicated 25-m2 plots were enriched with seed of the introduced grass, Lolium arundinaceum at an initial frequency of 50% infection by the systemic, seed-transmitted endophyte Neotyphodium coenophialum. Over 54 months, there was a significantly greater increase in endophyte-infection frequency in the presence of herbivores (30% increase) than where mammalian and insect herbivory were experimentally reduced by fencing and insecticide application (12% increase). Under ambient mammalian herbivory, the above-ground biomass of nonhost plant species was reduced compared with the mammal-exclusion treatment, and plant composition shifted toward greater relative biomass of infected, tall fescue grass. These results demonstrate that herbivores can drive plant-microbe dynamics and, in doing so, modify plant community structure directly and indirectly.

Soil Carbon and Nitrogen Pools in Response to Tall Fescue Endophyte Infection, Fertilization, and Cultivar

Tall fescue (Festuca arundinacea Schreb.) is an important cool‐season perennial forage used for grazing animals in the humid regions of the USA and throughout the world. The fungal endophyte Neotyphodium coenophialum Glenn, Bacon, & Hanlin naturally inhabits the majority of tall fescue stands producing a variety of alkaloids in leaf tissue that can cause animal health disorders on ingestion. We hypothesized that endophyte infection would modify the stock and activity of various soil C and N pools (total, particulate, microbial biomass, and mineralizable), but that fertilization (13.4–1.5–5.6 vs. 33.6–3.7–13.9 g N–P–K m−2 yr−1) and cultivar (‘Kentucky‐31’, K‐31; ‘AU‐Triumph’; and ‘Johnstone’) might alter these responses. Soil organic C and total N at a depth of 0 to 20 cm under K‐31 with high fertilization were greater with high (4197 g C m−2 and 266 g N m−2) than with low (3872 g C m−2 and 242 g N m−2) endophyte infection at the end of 20 yr. Under low fertilization, soil organic C and total N were not different between low and high endophyte infection. Differences in C and N pools among cultivars with low fertilization were as large as among K‐31 fertilization‐endophyte comparisons, but appeared to be related to factors other than endophyte infection frequency. Carbon and N contents of small macroaggregates (0.25–1.0 mm) were the only soil properties that were related (r = 0.70, P = 0.001) to endophyte infection frequency (range of 1–79%) across all treatments. Soil C and N pools can be modified by endophyte infection, but these results narrowed this phenomenon to (i) conditions of higher fertility and (ii) predominantly in small macroaggregates.

Seasonal and edaphic variation in VAM infection of fuel wood trees by Glomus mosseae

Seasonal differences in percentage length of fuel-wood host roots, viz., Albizia lebbeck, Acacia nilotica and Prosopis juliflora infected with Glomus mosseae were measured in five field sites in Mainpuri District of U.P. Highest G. mosseae infection levels were generally found in the rainy season in phosphorus deficient soils, low in moisture. The root sampled from the soils with a high soil-moisture content, fine endophyte infection increased to a maximum later in the growing season. A higher percentage frequency of fine endophyte infection on fine fuel-wood feeder roots in rainy season is taken as evidence for the hypothesis that G. mosseae is a vesicular arbuscular mycorrhizal fungus particularly adapted to penetrating host roots during brief seasonal fluxes of phosphorus availability. The implications of these data are discussed in relation to mechanisms in fuel-wood trees which adapt them to nutrient stress.

Particulate and non-particulate fractions of soil organic carbon under pastures in the Southern Piedmont USA

Pasture management can be effective at sequestering soil organic C. We determined the depth distribution of particulate organic C (POC), non-particulate organic C (NPOC), particulate-to-total organic C (POC-to-TOC) ratio, and particulate organic C-to-N (POC-to-N) ratio under pastures near Watkinsville, GA, USA. POC was highly related with total organic C (TOC), but became an increasingly larger portion of TOC near the soil surface, where both pools were greatest. POC and NPOC were (i) greater under pasture than under conservation-tillage cropland, (ii) greater when pasture was grazed than when hayed, (iii) marginally greater with higher fertilization of pasture, (iv) greater with higher frequency of endophyte infection of tall fescue, and (v) greater under increasing stand age of grass. Soil under pasture comparisons that had greater TOC content had (i) larger improvements in POC than in NPOC and (ii) lower POC-to-N ratios, suggesting improvement in biochemical soil quality, as well as soil C sequestration.

Changes of Endophyte Infection Frequency in Turf of Northeastern Honshu, Japan

Changes of Endophyte Infection Frequency in Turf of Northeastern Honshu, Japan

Effects of Endophyte Infection in Tall Fescue (Festuca arundinacea: Poaceae) on Community Diversity

Recent studies have suggested that the presence of endophytes in tall fescue can lead to decreased species richness in the associated plant community. To assess the generality of this hypothesis, a field study tested the effects of endophyte infection on a 3‐yr‐old successional field dominated by Festuca arundinacea. The potential importance of endophyte infection relative to other environmental factors was tested by including two additional treatments: the effects of soil fertility and mowing. Contrary to previous studies, a positive relationship was found between endophyte infection frequency and diversity ($$N=23$$ , $$F=5.23$$ , $$R^{2}=0.19$$ , $$P< 0.03$$ ). A strong interaction was found between the mowing treatment and endophyte infection frequency in predicting diversity ($$N=22$$ , $$F=36.1$$ , $$R^{2}=0.84$$ , $$P< 0.0001$$ ), where the maximum species richness was present in plots that were both mowed and highly endophyte infected. The relationship between endophytes and diversity varied through the successional continuum (the mowing treatments) but was generally positive. The soil in mowed plots was drier than in unmowed plots ($$t=2.1$$ , $$\mathrm{df}\,=28$$ , $$P< 0.05$$ ). We suggest that heavy mowing decreases soil moisture levels enough to reduce the interspecific competitive ability of infected F. arundinacea, thereby promoting local diversity. Endophyte presence is important, but the previously reported negative relationship between endophyte infection and community diversity is probably overly simplistic in complex ecological settings.

Endophyte Infection Levels of Native and Naturalized Fescues in Illinois and England

SPYREAS, G., D.J. GIBSON, AND M.A. BASINGER. (Department of Plant Biology, Southern Illinois University at Carbondale, Carbondale, IL 62901). Endophyte infection levels of native and naturalized fescues in Illinois and England. J. Torrey Bot. Soc. 128:25-34. 2001.-Fungal endophytes are thought to play a major role in the ecology of many cool-season grasses. However, the frequency of endophyte infection in the wild remains poorly known. Populations of wild fescues were tested for systemic fungal endophyte infection by taking samples from four native or naturalized species throughout southern Illinois (Festuca arundinacea, F. rubra, F. obtusa, and F. paradoxa), and one of these species (F. arundinacea) from native populations in England. The two grasses native to southern Illinois (F. obtusa and F. paradoxa) were highly infected (mean infection of 91 % and 100 %, respectively). The introduced grass F. rubra was uninfected. Festuca arundinacea showed variable levels of infection among populations in both southern Illinois and England (71 % and 64 %, respectively). The role of endophytes in natural systems is contingent upon infection levels that appear to vary widely among these four species. Furthermore, the use of agricultural cultivars may differentially affect infection levels of naturalized plants.

The ecology and evolution of endophytes

The association between tall fescue and its endophyte is the best-known case of a symbiosis that is widespread in grasses, especially in cool-season, pooid grasses. Field and herbarium surveys have shown that many grasses are endophyte infected, often at 100% frequency. Ubiquitos endophyte infection with a host species is prima facie evidence that the association is mutualistic since there are mechanisms by which individuals could lose the infection (e.g. extended seed dormancy). Studies have shown that the frequency of endophyte infection tends to increase over time, suggesting an ecological advantage for infected (E+) plants. A 3 year demographic experiment with tall fescue in a grassland community in Louisiana revealed that E+ plants had significantly higher survival growth and flowering rates than E-plants. The mean fitness of E+ ball fescue was twice the mean fitness of E-plants. Greenhouse and common garden experiments have shown that E+ plants generally perform better than E-plants in mixtures. In order to separate the effects of endophyte-induced physiological changes in hosts versus protection against herbivory, a series of factorial competition experiments have been conducted where infection status, insect herbivory, density, and the identity of competing species were controlled. Preliminary results indicate that both infection and herbivory can affect competitive interactions among plants. The high frequency of seed-borne Acremonium endophytes within species of genera like Festuca, Lolium, Poa, and Stipa suggests that the association originated before speciation within these genera. The association of clavicipitaceous fungi with grasses spans a great range of interactions from localized ovarian parasites (e.g. Claviceps), systemic, choke-inducing fungi (e.g. Atkinsonella, Balansia, Epichloë), epiphytic fungi ( Atkinsonella, some species of Balansia, Myriogenospora), and completely seed-borne, asymptomatic endophytes such as in Lolium. The question of what type of associations are ancestral and which are derived remains unanswered. The potential of these fungi for contagious spread and the presence or absence of a sexual reproductive system may influence genetic variation within taxa, and therefore their evolution and coevolution with grasses. Seed-borne Acremonium endophytes do not spread contagiously or reproduce sexually. They are reproductively isolated from other endophytes and can become genetically differentiated by the accumulation of random mutations. Isozyme electrophoresis has revealed abundant genetic variation in many Acremonium endophytes from wild grasses but, in contrast, artificial selection of cultivated grasses apparently has eliminated much genetic variation of endophytes. Future research on endophytes will focus on quantifying genetic variation for important traits such as alkaloid production, stroma formation, and host compatability.

Relationship between Level of Endophyte Infection and Cattle Gains on Tall Fescue

One hundred eighty yearling Holstein steers and heifers grazed a series of 2-acre tall fescue (Festuca arundinacea Schreb.) pastures over a three-year period. Pastures were infected with Acremonium coenophialum at levels from 3 to 83%. A significant overall relationship between endophyte infection frequency (EIF) and average daily gain (ADG) was described by the equation: ADG (lb/d) = 1.46 − 0.01 × EIF(%). Seasonal variation existed whereby spring-summer gains were reduced 0.15 lb/head/d for each 10% increase in EIF, while no relationship existed for fall grazing. Although the relationships between EIF and ADG were significant, low R2 values suggest other factors are involved. Still, the general relationship may be useful for estimating animal performance on tall fescue when EIF is known and for making economic decisions regarding management and renovation of infected tall fescue stands.

Ergopeptine Alkaloids in Grazed Tall Fescue

AbstractEndophyte (Acremonium coenophialum Morgan‐Jones et Gams) ‐infected tall fescue (Festuca arundinacea Schreb.) produces ergopeptine alkaloids (EP) that may be associated with fescue toxicosis symptoms in cattle (BOS taurus). A study was conducted during 1983 and 1984 at Watkinsville, GA, to determine the effects of endophyte infection, season, and N fertilization on EP concentration and steer average daily gain (ADG) in grazed 0.7‐ha tall fescue paddocks. Treatments included low (LF) and high (HF) endophyte infection frequency ‘Kentucky‐31’ (KY‐31) tall fescue fertilized with 134 or 336 kg N ha−1 (2✕2 factorial) replicated three times. The cultivars AU Triumph and Johnstone were also evaluated. Animals were managed using put‐and‐take grazing system. Ergopeptine alkaloid concentration (ergovaline was 80% of total) was greater in HF KY‐31 than LF KY‐31 in both years. Peak ergovaline concentrations occurred in spring and again in autumn (1984) when concentrations in HF KY‐31 approached 1 mk kg−1. Mid‐summer concentrations were about one‐third the autumn maximum for HF and LF KY‐31. Nitrogen fertilization had minimal effect on ergovaline concentration in the spring‐summer of 1983 but increased concentrations in LF KY‐31 in 1984. Ergopeptine alkaloids were not detected in endophyte‐free AU Triumph, and were detected in low amounts (< 0.1 mg kg−1) in a pre‐varietal release of Johnstone containing 7 to 10% endophyte. Increased ergovaline was associated with decreased ADG in the spring‐summer of 1983 and 1984; however, there was no significant association between ergovaline and ADG when the entire (April‐December) 1984 growing season was considered, suggesting that ergopeptine alkaloids may operate in conjunction with other environmental and nutritional factors to elicit fescue toxicosis symptoms.

Fungal Endophyte Infection‐Loline Derivative Alkaloid Concentration of Grazed Tall Fescue1

AbstractImpaired animal performance on tall fescue (Festuca arundinacea, Schreb.) pasture has been associated with the presence of a fungal endophyte (Acremonium coenophialum). A number of alkaloids, including the loline derivatives N‐formyl and N‐acetyl loline, occur in endophyte infected tall fescue. A study was conducted at Watkinsville, GA, on a Cecil sandy loam (Typic hapludult) to examine the influence of N fertilization and season on endophyte infection frequency (EIF) and loline derivative alkaloid concentration (LDA) of grazed low and high endophyte tall fescue. Paddocks (0.7 ha) established with low and high endophyte status ‘Ky‐31’ tall fescue seed were fertilized with 134 and 336 kg N ha−1 (22 factorial) and replicated three times. Endophyte infection frequency was greater in high than low fungus paddocks during the 3‐yr study. Endophyte infection frequency means within a given paddock, i.e., high or low fungus, remained relatively constant in 1983 and 1984 but increased by 50% in high and 100% in low fungus paddocks in 1985. Endophyte infection frequency was not affected by N nor did infection frequency vary significantly within a growing season. Loline derivative alkaloid concentration and EIF were significantly correlated (positive) in each growing season. High fungus paddocks had significantly greater (100%) LDA than low fungus paddocks. The ratio of LDA to EIF was greater under high N and high fungus conditions in the fall of 1983 and in 1984. Periods of LDA production may be more closely associated with short‐term weather conditions than absolute EIF. The relationship between LDA and EIF may not be simply defined in continuously grazed tall fescue, especially under moderate EIF.

SEASONAL AND EDAPHIC VARIATION IN VESICULAR‐ARBUSCULAR MYCORRHIZAL INFECTION OF GRASSES BY GLOMUS TENUIS

SummarySeasonal differences in percentage length of gramineous host root infected with Glomus tennis were measured in three field sites in Pennsylvania, U.S.A. Highest G. tennis infection levels were generally found in the spring in very phosphorus‐deficient soils low in moisture. In roots sampled from soils with a high spring soil‐moisture content, fine endophyte infection increased to a maximum later in the growing season. A higher percentage frequency of fine endophyte infection on fine grass feeder roots in spring is taken as evidence for the hypothesis that G. tenuis is a vesicular–arbuscular mycorrhizal fungus particularly adapted to penetrating host roots during brief seasonal fluxes of phosphorus availability. The implications of these data are discussed in relation to mechanisms in grasses which adapt them to nutrient stress.