Endophyte metabolites associated with perennial ryegrass toxicosis

Abstract

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.