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.

Rumen bacterial communities in forage-fed and grazing cattle continually adapt to a wide range of changing dietary composition, nutrient density, and environmental conditions. We hypothesized that very distinct community assemblages would develop between the fiber and liquid fractions of rumen contents in animals transitioned from bermudagrass hay diet to a grazed wheat diet. To address this hypothesis, we designed an experiment utilizing a 16S-based bTEFAP pyrosequencing technique to characterize and elucidate changes in bacterial diversity among the fiber and liquid rumen fractions and whole rumen contents of 14 (Angus x Hereford) ruminally cannulated steers sequentially fed bermudagrass hay (Cynodon dactylon; 34 days) and grazing wheat forage (28 days). Bermudagrass hay was a conserved C4 perennial grass lower in protein and higher in fiber (11% and 67%, respectively) content than grazed winter wheat (Triticum aestivum), a C3 annual grass with higher protein (20%) and a large (66%) soluble fraction.Significant differences in the OTU estimates (Chao1, Ace,and Rarefaction) were detected between fractions of both diets, with bermudagrass hay supporting greater diversity than wheat forage. Sequences were compared with a 16S database using BLASTn and assigned sequences to respective genera and genera-like units based on the similarity value to known sequences in the database. Predominant genera were Prevotella (up to 33%) and Rikenella-like (upto 28%) genera on the bermudagrass diet and Prevotella (upto 56%) genus on the wheat diet irrespective of the fractions. Principle component analyses accounted for over 95% of variation in 16S estimated bacterial community composition in all three fractions and clearly differentiated communities associated with each diet. Overall, bermudagrass hay diets clustered more clearly than wheat diets.These data are the first to explore bacterial diversity dynamics in a common population of animals in response to contrasting grass forage diets.

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.

Neotyphodium coenophialum, (Morgan-Jones & Gams) Glenn, Bacon & Hanlin, infected tall fescue (Festuca arundinacea Schreb.) plants perform better than non-infected isolines on phosphorus (P)-deficient soils. Our objective was to characterize growth and P uptake dynamics of tall fescue in response to endophyte infection and P source at low P availability in soil. Two tall fescue genotypes (DN2 and DN4) infected with their naturally occurring N. coenophialum strains (E+), and in noninfected (E-) forms were grown in Lily soil (fine loamy siliceous, mesic Typic Hapludult) in a greenhouse for 20 weeks. Three soil P treatments were imposed: no P supplied (control) and P supplied as commercial fertilizer (PF) or as phosphate rock (PR) at the level of 25 mg P kg -1 soil. Interaction of tall fescue genotype and endophyte status had a significant influence on mineral element uptake suggesting high 1 Corresponding author. 835 836 MALINOWSKI AND BELESKY specificity of endophyte-tall fescue associations. Endophyte infection did not affect root dry matter (DM) when no P was supplied but shoot DM was reduced by 20%. More biomass was produced and greater P uptake rate occurred in PR than PF treatment. Root DM was greater in E+ DN4 than E-DN4 when supplied with either PF or PR. In contrast, endophyte infection did not affect root DM of DN2, regardless of P source. Relative growth rate (RGR) of E+ plants grown with PR was 16% greater than that of E-plants. Endophyte infection did not improve growth or P uptake in PF treatment. When PR was supplied, P uptake rate was 24% greater in E+ DN2 than E-DN2, but endophyte infection did not benefit DN4. Phosphorus-use efficiency was 6% less in E+ DN2 but 16% greater in E+ DN4 compared to E-plants, regardless of P source. Root exudates of E+ DN2, but not E+ DN4 solubilized more P from PR than those of E-plants. The correlation between root RGR and P uptake rate was relatively high for E-plants (r=0.76), but low for E+ plants (r=0.27) grown with PR. Results suggest that P uptake by E+ tall fescue might rely on mechanisms other than an increase in root biomass (surface area). Endophyte infection modified tall fescue responses to P source. This phenomenon was associated with modes of P acquisition which included enhanced activity of root exudates in releasing P from PR in E+ plants (DN2), and increased root biomass (DN4). The dominant means of P acquisition may be determined by a specific association of endophyte and tall fescue genomes. Endophyte-tall fescue association plasticity contributes to widespread success of symbiotic in marginal resource conditions.

The three cool-season perennial forage grasses cocksfoot/orchardgrass, Dactylis glomerata L., tall fescue, Festuca arundinacea Schreb. syn. Lolium arundinaceum (Schreb.) Darbysh., and phalaris/harding grass, Phalaris aquatica L., are of major economic and ecological importance in regions with summer-dry environments. This review considers the constraints that these species are likely to experience under current and predicted increase of droughts due to climate change scenarios in south-eastern Australia, the southern Great Plains of USA and the Western Mediterranean Basin. The review identifies research required to maximise the development and use of C3 cool-season grasses with enhanced resilience to drought while considering the concern of some regulators that these grasses may be potential weeds. The state of knowledge of factors influencing plant drought survival and therefore recovery after stress and long-term persistence is discussed in the light of adaptive strategies. The major research needs identified to enhance traits conferring drought survival include (1) increasing the depth and density of grass root systems to strengthen dehydration avoidance; (2) exploring the biochemical, molecular and hydraulic bases of dehydration tolerance and improving techniques to measure this trait; (3) breaking the trade-off between summer dormancy and forage yield potential and improving understanding of environmental, biochemical and genetic controls over summer dormancy; (4) identifying non-toxic endophyte strains compatible with summer-dormant cultivars of tall fescue to enhance drought survival; and (5) enhancing seed production capability of new cultivars as well as the development of agronomic management packages for promoting stable mixtures combining perennial grasses and legumes. The weed potential of newly introduced summer-dormant cultivars is concluded to be minor. The research directions proposed here should improve pasture grass resilience and forage crop sustainability in Mediterranean and temperate summer-dry environments under the future drier and warmer conditions associated with climate change.

Infection of tall fescue (Festuca arundinacea Schreb.) with its endemic Neotyphodium coenophialum-endophyte (Morgan-Jones and Gams) Glenn, Bacon and Hanlin appears to reduce copper (Cu) concentrations in forage and serum of grazing animals, contributing to a range of immune-related disorders. A greenhouse experiment was conducted to identify effects of novel endophyte strains on Cu acquisition by tall fescue (Festuca arundinacea Schreb.) varieties Grasslands Flecha and Jesup infected with a novel, non ergot producing endophyte strain AR542, and two perennial ryegrass (Lolium perenne L.) varieties Aries and Quartet infected with a novel, non lolitrem B producing strain AR1, and their noninfected (E−) forms. Individual endophyte/grass associations were cultivated in nutrient solutions at 1.0 (P+) and 0.0 mM (P−) phosphorus concentrations. The Cu 2+ -binding activity of extracellular root exudates, and concentrations of Cu and other heavy metals in roots and shoots were measured. Extracellular root exudates of AR542-infected vs. E− tall fescue had higher Cu 2+ -binding activity only in P− nutrient solution as shown by lower concentration of free Cu 2+ (0.096 vs. 0.188 mmol Cu 2+ g −1 root DM, respectively). The Cu 2+ -binding activity by root exudates of perennial ryegrass was not affected by endophyte infection, but was higher (i.e., lower concentration of free Cu 2+ ) in P− vs. P+ nutrient solution (0.068 vs. 0.114 mmol Cu 2+ g −1 root DM). In this hydroponic experiment, Cu concentrations in shoots of both grasses were not a function of Cu 2+ -binding activity and endophyte effects on heavy metal concentrations in shoots and roots were specific for each variety. The Cu 2+ -binding activity of extracellular root exudates may affect Cu accumulation by field-grown, endophyte-infected tall fescue under P-limiting growth conditions and warrants verification by more specific methods.

Mechanisms involved in mineral stress tolerance of cool‐season grasses infected by Neotyphodium spp. endophytes are not known. In a controlled‐environment experiment, two genotypes (DN2 and DN4) of tall fescue (Festuca arundinacea Schreb.) infected (E+) with their naturally occurring strains of N. coenophialum (Morgan‐Jones and Gams) Glenn, Bacon and Hanlin, and their non‐infected (E−) isolines were cultivated in nutrient solution at two phosphorus (P) levels of 31 mg P dm−3 (P+) and 0.31 mg P dm−3 (P−) for 3 weeks. Diameters of lateral roots, root hair length, and distance between root hairs were recorded using a digital image analysis system (Dage 72S CCD camera controlled by a Power MacIntosh 7200/120PC compatible computer equipped with an AG‐5 frame grabber board and NIH‐Image). Irrespective of tall fescue genotype and P level in nutrient solution, E+ plants had roots with a smaller diameter (16 %) than E− plants. In response to P deficiency, root diameter of E+ plants declined by 11 % and root hair length increased by 17 % when compared to E− plants. Altered root diameter and root hair length might be one of the mineral stress tolerance mechanisms in endophyte‐infected tall fescue.

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