Comparison of Plant Metabolites in Root Exudates of Lolium perenne Infected with Different Strains of the Fungal Endophyte Epichloë festucae var. lolii

Lolium perenne infected with the fungal endophyte Epichloë festucae var. lolii have specific, endophyte strain-dependent, chemical phenotypes in their above-ground tissues. Differences in these chemical phenotypes have been largely associated with classes of fungal-derived alkaloids which protect the plant against many insect pests. However, the use of new methodologies, such as various omic techniques, has demonstrated that many other chemical changes occur in both primary and secondary metabolites. Few studies have investigated changes in plant metabolites exiting the plant in the form of root exudates. As root exudates play an essential role in the acquisition of nutrients, microbial associations, and defense in the below-ground environment, it is of interest to understand how plant root exudate chemistry is influenced by the presence of strains of a fungal endophyte. In this study, we tested the influence of four strains of E. festucae var. lolii (E+ (also known as Lp19), AR1, AR37, NEA2), and uninfected controls (E-), on L. perenne growth and the composition of root exudate metabolites. Root exudates present in the hydroponic water were assessed by untargeted metabolomics using Accurate-Mass Quadrupole Time-of-Flight (Q-TOF) liquid chromatography-mass spectrometry (LC-MS). The NEA2 endophyte strain resulted in the greatest plant biomass and the lowest endophyte concentration. We found 84 metabolites that were differentially expressed in at least one of the endophyte treatments compared to E- plants. Two compounds were strongly associated with one endophyte treatment, one in AR37 (m/z 135.0546 RT 1.17), and one in E+ (m/z 517.1987 RT 9.26). These results provide evidence for important changes in L. perenne physiology in the presence of different fungal endophyte strains. Further research should aim to connect changes in root exudate chemical composition with soil ecosystem processes.

Epichloë Endophyte Infection rates and Alkaloid Content in Commercially Available Grass Seed Mixtures in Europe

Fungal endophytes of the genus Epichloë live symbiotically in cool season grass species and can produce alkaloids toxic to insects and vertebrates, yet reports of intoxication of grazing animals have been rare in Europe in contrast to overseas. However, due to the beneficial resistance traits observed in Epichloë infected grasses, the inclusion of Epichloë in seed mixtures might become increasingly advantageous. Despite the toxicity of fungal alkaloids, European seed mixtures are rarely tested for Epichloë infection and their infection status is unknown for consumers. In this study, we tested 24 commercially available seed mixtures for their infection rates with Epichloë endophytes and measured the concentrations of the alkaloids ergovaline, lolitrem B, paxilline, and peramine. We detected Epichloë infections in six seed mixtures, and four contained vertebrate and insect toxic alkaloids typical for Epichloë festucae var. lolii infecting Lolium perenne. As Epichloë infected seed mixtures can harm livestock, when infected grasses become dominant in the seeded grasslands, we recommend seed producers to test and communicate Epichloë infection status or avoiding Epichloë infected seed mixtures.

A single exposure to the tremorgenic mycotoxin lolitrem B inhibits voluntary motor activity and spatial orientation but not spatial learning or memory in mice

The indole diterpenoid toxin lolitrem B is a tremorgenic agent found in the common grass species, perennial ryegrass (Lolium perenne). The toxin is produced by a symbiotic fungus Epichloë festucae (var. lolii) and ingestion of infested grass with sufficient toxin levels causes a movement disorder in grazing herbivores known as 'ryegrass staggers'. Beside ataxia, lolitrem B intoxicated animals frequently show indicators of cognitive dysfunction or exhibition of erratic and unpredictable behaviours during handling. Evidence from field cases in livestock and controlled feeding studies in horses have indicated that intoxication with lolitrem B may affect higher cortical or subcortical functioning. In order to define the role of lolitrem B in voluntary motor control, spatial learning and memory under controlled conditions, mice were exposed to a known dose of purified lolitrem B toxin and tremor, coordination, voluntary motor activity and spatial learning and memory assessed. Motor activity, coordination and spatial memory were compared to tremor intensity using a novel quantitative piezo-electronic tremor analysis. Peak tremor was observed as frequencies between 15 and 25Hz compared to normal movement at approximately 1.4-10Hz. A single exposure to a known tremorgenic dose of lolitrem B (2 mg/kg IP) induced measureable tremor for up to 72 h in some animals. Initially, intoxication with lolitrem B significantly decreased voluntary movement. By 25 h post exposure a return to normal voluntary movement was observed in this group, despite continuing evidence of tremor. This effect was not observed in animals exposed to the short-acting tremorgenic toxin paxilline. Lolitrem B intoxicated mice demonstrated a random search pattern and delayed latency to escape a 3 h post intoxication, however by 27 h post exposure latency to escape matched controls and mice had returned to normal searching behavior indicating normal spatial learning and memory. Together these data indicate that the tremor exhibited by lolitrem B intoxicated mice does not directly impair spatial learning and memory but that exposure does reduce voluntary motor activity in intoxicated animals. Management of acutely affected livestock suffering toxicosis should be considered in the context of their ability to spatially orientate with severe toxicity.

Development of a model for investigation of perennial ryegrass toxicosis in sheep

AIMS To develop a clinical model of perennial ryegrass toxicosis (PRGT) based on feeding a known dose of lolitrem B and ergotamine, and to produce a consistent clinical presentation for assessment of disease pathophysiology, neurological changes and neurohistopathology. METHODS Male lambs, aged between 10-12 months, were randomly assigned to either Treatment (n=9) or Control (n=9) groups. Lambs in the Treatment group received feed containing a novel endophyte-infested perennial ryegrass seed, commencing on Day 0 of the Feeding phase with a low induction dose, then increasing after 3 days to provide 0.16 mg/kg live bodywight (LBW)/day of lolitrem B and 0.054 mg/kg LBW/day ergotamine. Lambs were examined daily and when defined signs of PRGT were observed they were transferred to the Testing phase. Neurological examinations, assessment of gait, surface electromyography (EMG) and mechanosensory nociceptive threshold testing were carried out and blood samples collected during both phases of the trial, with a full necropsy, histopathological examination and measurement of faecal cortisol metabolites (FCM) performed on Day 2 of the Testing phase. RESULTS Typical clinical signs of PRGT, including ataxia of vestibulocerebellar origin leading to stumbling, were observed in all Treatment lambs. The median interval from the start of the Feeding phase to entry into the Testing phase was 21 (min 18, max 34) days. Histopathological characterisation of neurological lesions included the presence of Purkinje cell vacuolation, pyknotic granular layer neurons and proximal axonal Purkinje cell spheroids. Lesions were most apparent within the vestibulocerebellum. Mean root-mean-square voltages from triceps EMG increased in Treatment lambs between Feeding phase Day 0 and Testing phase Day 2 (p<0.001). Daily water intake during the Testing phase for the Treatment group was less than in Control group lambs (p=0.002), and concentrations of FCM at necropsy were higher in Treatment compared to Control lambs (p=0.02). CONCLUSIONS AND CLINICAL RELEVANCE Lolitrem B and ergotamine dosing in feed on a live weight basis combined with neurological/gait assessment provides an effective model for investigation of PRGT and potential therapeutics. Assessment of gait changes using defined criteria and RMS voltages from EMG appear to be useful tools for the assessment of the severity of neurological changes.

Lolitrem B and Indole Diterpene Alkaloids Produced by Endophytic Fungi of the Genus Epichloë and Their Toxic Effects in Livestock

Different group of alkaloids are produced during the symbiotic development of fungal endophytes of the genus Epichloë in grass. The structure and toxicity of the compounds vary considerably in mammalian herbivores and in crop pests. Alkaloids of the indole-diterpene group, of which lolitrem B is the most toxic, were first characterized in endophyte-infected perennial ryegrass, and are responsible for “ryegrass staggers.” Ergot alkaloids, of which ergovaline is the most abundant ergopeptide alkaloid produced, are also found in ryegrass, but generally at a lower rate than lolitrem B. Other alkaloids such as lolines and peramine are toxic for crop pests but have weak toxicological properties in mammals. The purpose of this review is to present indole-diterpene alkaloids produced in endophyte infected ryegrass from the first characterization of ryegrass staggers to the determination of the toxicokinetics of lolitrem B and of their mechanism of action in mammals, focusing on the different factors that could explain the worldwide distribution of the disease. Other indole diterpene alkaloids than lolitrem B that can be found in Epichloë infected ryegrass, and their tremorgenic properties, are presented in the last section of this review.

Endophyte metabolites associated with perennial ryegrass toxicosis

Perennial ryegrass (PRG) was analysed for alkaloids associated with the expression of perennial ryegrass endophyte toxicosis (PRGT) in south-east Australia. Over two seasons, the PRG cultivar Samson (‘high endophyte’, viz. naturally infected with a wild-type strain of Epichloë festucae var. lolii) was sampled on five occasions during November to May at four farms in Victoria and at Lincoln, New Zealand. Endophyte frequency in the populations was 77–100%. PRG was also sampled from 20 Victorian and Tasmanian farm pastures where stock were experiencing PRGT (endophyte infection frequencies of 87–100%). The Victorian summer of 2010–11 was atypically moist; pasture remained green. Lolitrem B was consistently high at Lincoln and 2–3 times that observed in Victorian samples of isogenetic PRG, or in PRG causing PRGT; it was the dominant toxin in 2011 with concentrations commonly exceeding the tolerance level of 1.8 mg/kg. In the following year, one with a more typical summer, ergovaline was the dominant toxin. Liquid Chromatography–Mass Spectrometry/Mass Spectrometry (LC-MS/MS) was carried out to determine indole diterpene intermediates in the lolitrem B biosynthesis pathway and for ergot alkaloid intermediates in the ergovaline pathway. The values for lolitrem B determined by LC-MS/MS correlated strongly with those obtained using high pressure liquid chromatography. In both Years 1 and 2, significantly higher expression was observed in the Lincoln relative to Victorian samples of PRG for paspaline, terpendole C, lolitrem E, lolitrem B and lolitrem F. For the ergot alkaloids, significant differences were not apparent between Victorian and Lincoln samples in Year 1. In Year 2, LC-MS/MS results showed ergovaline concentrations were greater in Victorian samples. In addition to endophyte-produced toxins, ergot alkaloids produced by Claviceps purpurea (ergotamine, ergocryptine and ergocornine) were detected in grass samples on 6/27 occasions. Some unidentified metabolites were noted in both Victorian and Lincoln samples. The effects of ingested vaso-constrictive ergot alkaloids combined with that of high solar radiation on ruminants’ heat load are considered most important with respect to the occasionally severe expression of PRGT in Australia.

Ergovaline and lolitrem B concentrations in perennial ryegrass in field culture in southern France: distribution in the plant and impact of climatic factors

Perennial ryegrass (Lolium perenne) infected by Epichloë festucae var. lolii contains alkaloids that are responsible for toxicosis in several countries, but few cases are reported in Europe. Lolitrem B is generally the most abundant alkaloid and is recognized to be responsible for livestock staggers, whereas ergovaline is less frequently documented in perennial ryegrass. Lolitrem B and ergovaline were monitored over a three-year period in endophyte-infected perennial ryegrass 'Samson' sown in southern France. Alkaloid concentrations were strongly influenced by the stage of maturity of the plant; maximum concentrations were always measured at the fully ripe stage. Over the three years of analysis, variations in lolitrem B in the whole plant at the fully ripe stage were low (from 1296 to maximum 1871 μg/kg dry matter), whereas ergovaline varied considerably (from 526 to 2322 μg/kg dry matter), suggesting that abiotic factors play a key role in determining ergovaline levels in endophyte-infected perennial ryegrass.

Evidence of dehydration and electrolyte disturbances in cases of perennial ryegrass toxicosis in Australian sheep

CASE REPORT

Perennial ryegrass toxicosis (PRGT) is a common disease entity in Australia, presenting as an association of clinical signs including alterations in normal behavioural, ataxia ('staggers'), ill thrift and gastrointestinal dysfunction ('scours'). Clinical signs can range in severity from mild (gait abnormalities and failure to thrive) to severe (seizures, lateral recumbency and death). Presentation across the flock is usually highly variable. PRGT is caused by toxins produced by the endophytic fungus Neotyphodium lolii, a symbiont of perennial ryegrass that is present in pastures across the temperate regions of Australia and Tasmania. A particular feature of PRGT in Australia is the occasional occurrence of large-scale sheep losses, suggesting other factors are influencing mortality rates compared with other PRGT risk zones such as North America and New Zealand. During 2011, producers in the state of Victoria experienced a mild outbreak of PRGT that affected large numbers of animals but with limited mortalities. Clinical samples taken from affected sheep showed a high incidence of dehydration and electrolyte abnormalities.

CONCLUSION

We speculate that changes in hydration status may be a contributory aetiological factor in those years in which high numbers of deaths are associated with PRGT outbreaks in Australia.

Forages and pastures symposium: fungal endophytes of tall fescue and perennial ryegrass: pasture friend or foe?

Tall fescue [Lolium arundinaceum (Schreb.) Darbysh. syn. Festuca arundinacea Schreb.] and perennial ryegrass (Lolium perenne L.) are important perennial forage grasses utilized throughout the moderate- to high-rainfall temperate zones of the world. These grasses have coevolved with symbiotic fungal endophytes (Epichloë/Neotyphodium spp.) that can impart bioactive properties and environmental stress tolerance to the grass compared with endophyte-free individuals. These endophytes have proven to be very important in pastoral agriculture in the United States, New Zealand, and Australia, where forage grasses are the principal feed for grazing ruminants. In this review, we describe the biology of these grass-endophyte associations and implications for the livestock industries that are dependent on these forages. Endophyte alkaloid production is put in context with endophyte diversity, and we illustrate how this has facilitated utilization of grasses infected with different endophyte strains that reduce livestock toxicity issues. Utilization of tall fescue and use of perennial ryegrass in the United States, New Zealand, and Australia are compared, and management strategies focused predominantly on the success of endophyte-infected perennial ryegrass in New Zealand and Australia are discussed. In addition, we consider the impact of grass-endophyte associations on the sustainability of pasture ecosystems and their likely response to future changes in climate.

Effects of wild-type, AR1 and AR37 endophyte-infected perennial ryegrass on dairy production in Victoria, Australia

A 3-year experiment compared the effects of wild-type ryegrass endophyte and two novel endophytes on milk production in dairy cattle. On three 9.9-ha farmlets in West Gippsland, Victoria, pasture swards were established that were dominant in perennial ryegrass (Lolium perenne) infected with either wild-type, AR1 or AR37 endophytes. Each farmlet was stocked with 25 spring-calving Holstein–Friesian cows, which rotationally grazed nine paddocks within their farmlet during three lactations over 3 years. The three endophytes are known to produce different alkaloids, with wild-type producing ergot alkaloids, lolitrems and peramine, AR1 producing peramine and AR37 producing epoxy-janthitrems. These alkaloids were present in fresh pasture as well as hay and silage made from that pasture. Grazed pasture comprised 53% of estimated annual DM intake. The proportion was least from December to March when the daily ration of 2 kg DM/cow.day cereal grain was increased to 6 kg/day and forage supplements were fed consisting of purchased lucerne (Medicago sativa) hay and pasture silage grown on the farmlets. There were no differences in pasture accumulation rates or nutritive characteristics of ryegrass pastures on the three farmlets and no differences in the production of milk, fat or protein by cows grazing pasture infected with the three endophytes. Ryegrass staggers was only observed in four cows consuming the wild-type-infected ryegrass in the first year when the highest concentrations of lolitrem B were recorded in pasture. Soil samples showed lower numbers of root aphids (Aploneura lentisci), mealybugs (Pseudococcidae) and pasture tunnel moths (Philobota spp.) beneath ryegrass infected with the AR37 endophyte compared with the other two endophytes. Numbers of redheaded (Adoryphorus couloni) and blackheaded (Aphodius tasmaniae) cockchafers did not differ between treatments. Under dairy management and supplementary feeding regimes common to south-eastern Australia, the novel endophytes AR1 and AR37 had no effect on the milk production compared with the wild-type endophyte, and did not cause ryegrass staggers.

Fluctuations in the concentration of ergovaline and lolitrem B produced by the wild-type endophyte (Neotyphodium lolii) in perennial ryegrass (Lolium perenne) pasture

Mammalian toxins produced by the wild-type endophyte, Neotyphodium lolii, in perennial ryegrass (PRG) pasture cause production losses and animal health and welfare problems in livestock. Managing this risk is limited by the lack of information on fluctuations in the concentration of toxin in Australian pasture. We investigated how the toxin concentrations may be related to recent observations of weather. Swards sown from common seedlots of two cultivars of wild endophyte-infected PRG, grazed short by sheep, were sampled at 2–4 weekly intervals from spring to autumn at two sites in Victoria. The highest concentration of ergovaline and lolitrem B was observed at Hamilton, the site with the longer-growing season. The concentration of ergovaline peaked in early summer, coinciding with seed development, and declined through summer, before increasing with the commencement of autumn growth. The concentration of lolitrem B remained low in summer, then rose in autumn. Variation between the two cultivars in the concentration of toxins was small and rarely significant. The concentration of ergovaline declined as the mean daily maximum temperature over the preceding 1–5 days increased. Similarly, for lolitrem B, the concentration declined over the temperature range 12−20°C, from 1.3 to 0.3 mg/kg. At Hamilton, where solar radiation and soil temperature were recorded, both were superior to maximum temperature for predicting lolitrem B. Serial sampling of PRG from old naturalised pasture on seven farms across south-eastern Australia found two seasonal peaks for both alkaloids in most pastures. The concentration of ergovaline reached or exceeded tolerance levels for livestock in 23 of 43 samples, compared with 5 of 43 for lolitrem B. Ergovaline concentrations initially peaked (at 1.0–1.6 mg/kg) when mature reproductive material was present (coinciding with peduncle elongation and seed development). In pastures with low grazing pressure, i.e. where growth was allowed to continue through summer, ergovaline concentration was relatively low (<0.7 mg/kg) but in a hard-grazed pasture (sward height 3 cm), the ergovaline concentration was greater (up to 1.1 mg/kg). Concentration of lolitrem B also peaked in December, except on pasture where growth continued through summer. High concentrations of lolitrem B associated with neurotoxic signs in sheep (viz. 2.4–3.9 mg/kg) were observed only in mid-summer and autumn, and only if conditions favoured growth or where close grazing by sheep left the crown as the dominant source of herbage.