Epichloae endophytes of family Clavicipitaceae (comprising genera Epichloë and Neotyphodium) are fungal symbionts of Pooideae grasses. The associations formed, range from mutually beneficial to antagonistic and the nature of this relationship is dependent upon the importance of vertical (via host seeds) versus horizontal (ascospore mediated) transmission of the fungus. These endophytes can enhance their hosts’ survival through protection from abiotic and biotic stresses and can thus be utilized in an agricultural context. Animal-safe grass-endophyte associations that confer bio-protective properties for increased pasture persistence and productivity have been developed and commercialized. One of the crucial drivers underpinning the selection of epichloae strains for commercial development is endophyte derived bioactivity. The potential of next generation endophytes is determined by testing a number of attributes such as agronomic fitness, animal and food safety as well as compatibility with host plants of interest. Strategic research supports these activities by focusing on elucidating mechanisms of compatibility between host and fungal symbiont, as well as investigating other molecular drivers of symbiosis such as siderophore mediated iron-uptake, fungal signalling, fungal growth in host plants and fungal secondary metabolism. This review weaves together the different strands of multidisciplinary research aimed at ultimately exploiting epichloae endophytes for increased pasture performance.

Tall fescue [Lolium arundinaceum (Schreb.) Darbysh. syn. Festuca arundinacea Schreb.] and perennial ryegrass (Lolium perenne L.) are important perennial forage grasses utilized throughout the moderate- to high-rainfall temperate zones of the world. These grasses have coevolved with symbiotic fungal endophytes (Epichloë/Neotyphodium spp.) that can impart bioactive properties and environmental stress tolerance to the grass compared with endophyte-free individuals. These endophytes have proven to be very important in pastoral agriculture in the United States, New Zealand, and Australia, where forage grasses are the principal feed for grazing ruminants. In this review, we describe the biology of these grass-endophyte associations and implications for the livestock industries that are dependent on these forages. Endophyte alkaloid production is put in context with endophyte diversity, and we illustrate how this has facilitated utilization of grasses infected with different endophyte strains that reduce livestock toxicity issues. Utilization of tall fescue and use of perennial ryegrass in the United States, New Zealand, and Australia are compared, and management strategies focused predominantly on the success of endophyte-infected perennial ryegrass in New Zealand and Australia are discussed. In addition, we consider the impact of grass-endophyte associations on the sustainability of pasture ecosystems and their likely response to future changes in climate.

The main plant species relied on for forage supply to grazing animals in New Zealand and south-eastern Australia is perennial ryegrass (Lolium perenne L.). Perennial ryegrass has evolved with a fungal endophyte (Neotyphodium lolii, Latch, Christensen & Samuals) that occupies intercellular spaces, and is nourished by its host. The endophyte (referred to as standard or wild-type) provides the plant with protection from a range of insect pests by producing alkaloids, some of which are also toxic to grazing animals, causing ryegrass staggers and/or exacerbating heat stress. Over the last 20 years naturally occurring perennial ryegrass endophytes have been found in Europe that produce less of the alkaloids that cause animal health problems but have similar or enhanced effects as the standard endophyte on deterring insect attack on infected plants, when introduced into New Zealand and Australian-bred ryegrasses. This review provides a summary of endophyte research in New Zealand from the perspective of insect pests, plants (particularly perennial ryegrass) and the animals grazed on ryegrass-dominant pastures. The protocols used to evaluate perennial ryegrass/endophyte associations over the past 30 years are also discussed. Future testing of new grass/endophyte associations should include the utilisation of more environments for agronomic and entomological experiments; routinely carrying out small animal toxicology assays, and the running of short-term indoor feeding experiments with sheep and cows. Implementation of these changes provides the minimum requirements for strengthening the evaluation of new endophyte associations so farmers using these technologies, gain optimal benefits from their adoption.