Loline alkaloids produced by Epichloe occultans in Australian Lolium rigidum

Annual ryegrass (Lolium rigidum Gaudin) is the most significant weed of southern Australian farming systems, causing an estimated $300 million in yearly losses to the grains industry (Pratley, pers.comm.). Annual ryegrass is frequently found in association with the endophytic fungus Epichloë occultans(C.D.Moon, B.Scott and M.J.Chr.). Fungal endophytes are known to provide ecological fitness benefits to many cool season grasses in part through production of different classes of bioactive compounds. However, it is unknown if E. occultans causes benefit or detriment to annual ryegrass through this association. This
study examines the production of the most prevalent alkaloids known to be produced by Epichloë spp., the lolines, in 15 Australian ecotypes of annual ryegrass. Loline alkaloids are known to enhance host survival
in other cool season grasses through protection from insect damage. A broad geographic selection of Australian biotypes of annual ryegrass naturalised to cropping areas based on endophyte presence in the seed was evaluated. Plants of each ecotype were grown and inspected for living endophyte presence before sampling. Loline alkaloids were assessed using GC-FID, including predominant natural variants of lolines; N-acetylloline (NAL), N-formylloline (NFL) and N-acetylnorloline (NANL). Total lolines measured in the plant samples ranged from 0–1200
ppm. Concentrations of NFL were consistently higher than NANL concentrations, whereas NAL was not detected in any of the samples. These results show the presence of lolines in infected L. rigidum in all areas sampled across southern Australia. The widespread production of loline alkaloids implies an ecological role in L. rigidum, likely associated with persistence of annual ryegrass through protection from herbivores.