Adaptations of Endophyte‐Infected Cool‐Season Grasses to Environmental Stresses: Mechanisms of Drought and Mineral Stress Tolerance

Abstract

Cool‐season grasses infected with Neotyphodium spp. endophytes have an extraordinary impact on the ecology and economy of pasture and turf. A range of adaptations of endophyte‐infected grasses to biotic and abiotic stresses has been identified but mechanisms of these adaptations are not clearly understood. In this review, we present recent research progress on endophyte‐related mechanisms affecting abiotic (drought, mineral) and selected aspects of biotic stress tolerance in cool‐season grasses. Endophytes induce mechanisms of drought avoidance (morphological adaptations), drought tolerance (physiological and biochemical adaptations), and drought recovery in infected grasses. Mineral nutrition (nitrogen, phosphorus, calcium) affects production of ergot alkaloids, thus understanding mechanisms involved in mineral economy of endophyte‐infected grasses will help in developing management practices to reduce forage toxicity to livestock. Previous research resolved the role of endophyte in nitrogen (N) economy of tall fescue. We identified two endophyte‐related mechanisms in tall fescue operating in response to phosphorus (P) deficiency. The mechanisms are altered root morphology (reduced root diameters and longer root hairs) and chemical modification of the rhizosphere resulting from exudation of phenolic‐like compounds. These mechanisms were shown to benefit endophyte‐infected plants grown under P deficiency. We also report a mechanism of aluminum (Al) sequestration on root surfaces in endophyte‐infected tall fescue, which appears to be related to exudation of phenolic‐like compounds with Al‐chelating activity. Understanding mechanisms of abiotic stress tolerance in endophyte‐infected grasses is essential for continued improvement and persistence of grasses for a range of applications, e.g., forage for semi‐arid areas or cover plants for soil renovation.

Fungal endophytes and their interaction with plant pathogens: a review

“…In contrast, other experiments showed that the amount of ergot alkaloids translocated to roots is very small, and experiments with Neotyphodium knockout mutants having their pathway of ergot alkaloid synthesis disrupted suggested that these alkaloids are not responsible for the inhibition of nematode populations in endophyte infected plants (Panaccione et al, 2006). Nevertheless, other types of alkaloids with antiherbivore activity are produced by Neotyphodium species, and chemical changes such as the production of phenolic compounds do occur in Neotyphodium-infected roots (Malinowski and Belesky, 2000). In conclusion, Neotyphodium endophytes provide host plants with protection against several nematode species, but the mechanism of action underlying this process is still unknown.…”

Isolation and Identification of Fungal Endophytes from Grasses along the Oregon Coast

“…Parasitic, saprophytic and pathogenic fungi can be very deleterious to a plant, while endophytes and mycorrhizal fungi are considered beneficial symbionts which promote plant growth, confer enhanced resistance to various pathogens and pests, and improve survival under unfavorable environmental conditions [4] [5] [25] (reviewed in [56]). Several endophytes identified in this study have previously been shown to promote plant growth under normal and/or stressed conditions.…”

A review of summer-active tall fescue use and management in Australia's high-rainfall zone

“…It was suggested by Malinowski & Belesky (2000) that tall fescue cultivars containing novel endophytes have a wider zone of adaptation than endophyte-free cultivars and are more drought tolerant. This may enable novel endophyte cultivars of tall fescue to be used in rainfall zones that are marginal for endophyte-free cultivars.…”