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.
Mode of action of tremorgens