Incidence of ryegrass endophyte (Neotyphodium lolii) and diversity of associated alkaloid concentrations among naturalised populations of perennial ryegrass (Lolium perenne L.)

Abstract

The mutualistic association between perennial ryegrass (Lolium perenne L.) and the ryegrass endophyte Neotyphodium lolii (Latch, Christensen and Samuels) Glenn, Bacon and Hanlin, previously assigned to the genus Acremonium, is known to have a major impact on pasture and animal production. The perennial ryegrass ecotypes Victorian and Kangaroo Valley are the most widely sown varieties of grass in Australian pasture. The incidence of ryegrass endophyte (N. lolii) in these ecotypes, and the production of alkaloids associated with theryegrass endophyte, are largely unexplored. Fifty-six populations of Victorian and 45 of Kangaroo Valley were sampled from old pasture within the recognised zones of naturalisation of both ecotypes. All of the 101 populations examined were infected with ryegrass endophyte. The mean ryegrass endophyte (N. lolii) frequency for plants within the populations of the Victorian and Kangaroo Valley ecotypes was 88% and 93%, respectively.

Alkaloid concentrations were determined from infected plants for 39 Kangaroo Valley populations and, in a separate study, for 24 Victorian populations. Ergovaline concentration was above the critical level of 0.4 mg/kg (above which clinical symptoms are observed) for 10% of the Kangaroo Valley populations and 17% of the Victorian populations. For lolitrem B, all Victorian populations were below the critical level of 1.8 mg/kg, but 28% of the Kangaroo Valley populations had mean concentrations above the critical level, 1.8 mg/kg. Concentrations for individual plants were <5 mg/kg for ergovaline, <6 mg/kg for lolitrem B, and <48 mg/kg for peramine. Within each ecotype examined, significant variation (P < 0.05) in the mean concentrations of ergovaline, lolitrem B, and peramine was found between the populations of naturalised perennial ryegrass. Mean concentrations for some of the various naturalised populations were higher than that observed in some of the control cultivars. Low ergovaline and lolitrem B concentrations observed for individual genotypes indicate scope for selecting grass endophyte combinations characterised by optimum production of alkaloids.