Ecological importance of Neotyphodium spp. grass endophytes in agroecosystems

Neotyphodium spp. fungal endophytes form symbiotic associations with agronomic grasses with expression ranging from mutualistic to parasitic. In general, endophyte infection frequencies seem more variable in natural compared to pastoral situations, suggesting that expression and benefits attributable to endophyte infection depend on the resource environment in which the host–endophyte complex was formed and the conditions under which it is being grown. Emerging evidence suggests that expression is not always mutualistic or beneficial to the host in terms of productivity and persistence in resource-limited environments. Expression of host–endophyte associations will vary depending on resource availability and environmental conditions that influence host physiology and growth, and herbivore behavior. New research suggest alkaloids and secondary metabolites produced by host–endophyte associations can have physiological functions in addition to acting as herbivore deterrents. Novel host–endophyte associations are being created that maintain insect and disease resistance, while having minimal detrimental impact on mammalian herbivores. The influence of host–endophyte associations on sward composition and soil food webs is only now coming to light. While novel endophyte associations and their attendant mechanisms can be considered beneficial in some respect, the associations may not be as adaptable to stressful or marginal resource environments and could have long-term ecological impacts measured in terms of persistence and total productivity of the sward. We review the extensive published work on host–endophyte interactions and illustrate the complexity of host–endophyte associations and their interactions with environment, and the range of responses that occur.