Stability and purity of Epichloë endophyte infection in New Zealand ryegrass pastures

Perennial ryegrass (Lolium perenne) in New Zealand pastures is typically infected with the mutualist Epichloë fungal endophyte, which assists the plant in resisting biotic and abiotic stresses. Ryegrass that has naturalised in New Zealand is highly infected with the ‘Standard’ strain of endophyte. This strain provides good protection from a range of invertebrate pests but negatively impacts livestock productivity and health in the warmer seasons of the year. Grass-endophyte associations have been developed between elite perennial ryegrass cultivars and selected endophyte strains to provide protective properties to the host plant and lessen or eliminate the negative effects on animals. While Epichloë-ryegrass associations have been intensively monitored in experimental trials, little has been measured and reported from dairy pastures grazed in commercial settings, particularly with regards to ingress of Standard endophyte. Here we report on presence of endophyte infection and endophyte strain in ryegrass tillers from dairy pastures sampled for up to 7 years in regions of the North and South Islands. In general, infection levels were high (mean 86%). The sown, selected endophytes were the dominant endophyte strains present and these were stable over time. This demonstrates that the industry has been successfully delivering ryegrasses infected with selected endophytes on to dairy farms. The frequency of non-sown endophytes was greater in the North (mean 8%, and mostly Standard endophyte) than the South Island (2%), and Standard endophyte increased over time. There were some notable exceptions to these general effects. Of 23 pastures, two failed to achieve the 70% minimum infection for endophyte to effectively protect against invertebrate pests, and three out of 23 developed high levels of contamination from Standard endophyte. In two cases, the management practices could have contributed to the poor outcome but otherwise the drivers for the low infection or increases in Standard endophyte are unknown.