Search

Grasses have developed a wide range of morphological and physiological mechanisms to resist herbivory. For instance, they accumulate silicon (Si) in tissue, as physical defence, and associate symbiotically with foliar Epichloë‐endophytes that provide chemical defence via antiherbivore alkaloids. Recent evidence showed that some Epichloë‐endophytes increase foliar Si in forage grasses; however, whether this impacts insect herbivores is unknown. Furthermore, while Si is primarily a physical defence, it also affects production of plant defensive secondary metabolites; Si supply might therefore affect Epichloë‐alkaloids, although this remains untested.We grew endophyte‐free (Nil) and Epichloë‐infected tall fescue and perennial ryegrass in a factorial combination with or without Si supplementation, in the absence or presence of Helicoverpa armigera. Epichloë‐endophyte strains were AR584 for tall fescue, and AR37, AR1 or Wild‐type (WT) for perennial ryegrass. We assessed how Si supply and Epichloë‐endophytes in interaction with herbivory affected foliar Si and mutualist‐derived alkaloid concentrations. Subsequently, their effects on H. armigera relative growth rates (RGRs) were evaluated.Endophytes generally increased Si concentrations in Si‐supplied plants. In tall fescue AR584 and perennial ryegrass AR37, endophytes increased constitutive (herbivore‐free) and induced (herbivore‐inoculated) Si concentrations by at least 25%; in contrast, in perennial ryegrass, the AR1 endophyte only increased constitutive levels. Si supply did not affect alkaloids produced by AR584 or AR1/WT endophytes; however, in the presence of herbivory, Si supply decreased the induction of alkaloids produced by AR37 endophytes by 33%. For tall fescue, Si supply reduced H. armigera RGR by at least 76%, regardless of endophytic status, whereas, endophyte‐alkaloids played a secondary role only reducing herbivore growth in the absence of Si supply. Conversely, in perennial ryegrass, both Si and endophyte‐alkaloids (regardless of Si supply) reduced herbivore RGR although not synergised.Novel interactions between constitutive and induced Si‐ and alkaloid‐based antiherbivore defences in grasses were observed. Overall, Si had a greater effect on the folivore than endophytes in both grasses. Endophyte defences contributed more to herbivore resistance in perennial ryegrass than tall fescue. We demonstrate that Si and endophytes were not antagonistic and highlight that the protective nature of their interaction varies with the grass‐endophyte species tested. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The symbiotic Epichloë festucae var. lolii endophyte produces alkaloids which can provide its host grass, perennial ryegrass (Lolium perenne L), with a selective advantage in both natural and agricultural managed ecosystems. This study focuses on understanding the alkaloid concentrations that occur in endophyte-infected perennial ryegrass during the early establishment phase. In a glasshouse experiment fungal alkaloid concentrations (peramine, lolitrem B, ergovaline, and epoxy-janthitrems) were measured in perennial ryegrass seedlings infected with E. festucae var. lolii proprietary strains AR1, AR37, NEA2, and NZ common toxic for 69 days after sowing. The endophyte becomes metabolically active, starting alkaloid production, as early as 6 days after sowing. Alkaloid concentrations peaked in 8- to 10- day-old seedlings due to a seedling growth slowdown. This study provides data showing that the loss of insect protection in endophyte-infected seedlings is linked to a reduction in chemical defence after seed-stored, maternally synthesised alkaloids are diluted by seedling dry matter accumulation. [ABSTRACT FROM AUTHOR]

The original version of this article unfortunately contained a mistake. There is a mistake in the affiliation section and Figure 6. The correct affiliation and Figure 6 are shown here. [ABSTRACT FROM AUTHOR]

A trade‐off between growth and defence against biotic stresses is common in plants. Fungal endophytes of the genus Epichloë may relieve this trade‐off in their host grasses since they can simultaneously induce plant growth and produce antiherbivore alkaloids that circumvent the need for host defence. The Epichloë ability to decouple the growth‐defence trade‐off was evaluated by subjecting ryegrass with and without Epichloë endophytes to an exogenous treatment with gibberellin (GA) followed by a challenge with Rhopalosiphum padi aphids. In agreement with the endophyte‐mediated trade‐off decoupling hypothesis, the GA‐derived promotion of plant growth increased the susceptibility to aphids in endophyte‐free plants but did not affect the insect resistance in endophyte‐symbiotic plants. In line with the unaltered insect resistance, the GA treatment did not reduce the concentration of Epichloë‐derived alkaloids. The Epichloë mycelial biomass was transiently increased by the GA treatment but at the expense of hyphal integrity. The response of the phyllosphere bacterial microbiota to both GA treatment and Epichloë was also evaluated. Only Epichloë, and not the GA treatment, altered the composition of the phyllosphere microbiota and the abundance of certain bacterial taxa. Our findings clearly demonstrate that Epichloë does indeed relieve the plant growth‐defence trade‐off. Summary statement: A debate has been raised if fungal endophytes can relieve the plant growth‐defence trade‐off. Epichloë endophytes decoupled the trade‐off: the growth‐mediated penalisation of plant defences was observed in E− but not in E+ plants. The Epichloë production of alkaloids was likely the decoupling mechanism. [ABSTRACT FROM AUTHOR]

Context: Data are lacking on the effects of selected endophytes of perennial ryegrass (Lolium perenne L.) on ryegrass persistence. Aim: We aimed to determine the impact of Epichloë endophyte on the persistence of mid- and late-heading perennial ryegrass cultivars. Method: Two mid-heading (Samson, Bronsyn) and two late-heading (One50, Rohan) cultivars, infected with selected endophytes (AR37, nea2/6) or with standard toxic endophyte, were established in a replicated plot study grazed by cattle in a subtropical environment of the upper North Island of New Zealand. Persistence characteristics were quantified at least five times per annum, over 4 years. Key results: Endophyte strain had an effect on persistence; infection with standard endophyte resulted in higher ryegrass ground cover percentage, ryegrass content in pasture dry matter and autumn yield than infection with nea2/6 on many occasions, and with AR37 on some occasions. There were negligible impacts on ryegrass tiller density or nutritive value. Trends were dominated by the main effect of endophyte; interactions with heading date were inconsistent. Conclusions: Cultivars were more persistent when infected with standard endophyte than with selected endophytes, although persistence declined over 4 years for all cultivars and irrespective of heading date. Implications: Reliance on selected endophyte is unlikely to prevent persistence decline of perennial ryegrass in a subtropical environment. Other strategies will be required to maintain the persistence of high-quality pastures based on perennial ryegrass. We determined the impact of endophyte strain (standard toxic endophyte, selected strains nea2/6 and AR37), on the persistence of four perennial ryegrass cultivars. Standard endophyte resulted in greater persistence than the selected endophytes, with higher ryegrass ground cover percentage and content in pasture dry matter by the end of the study, and higher herbage yields in autumn. Persistence declined over 4 years for all cultivars, regardless of endophyte. [ABSTRACT FROM AUTHOR]

Context: Data are lacking on the effects of heading date of perennial ryegrass (Lolium perenne L.) on ryegrass persistence. Aim: We aimed to determine the impact of heading date on perennial ryegrass persistence. Method: Two mid-heading (Samson, Bronsyn) and two late-heading (One50, Rohan) cultivars, infected with Epichloë endophytes (AR37, nea2/6 or standard toxic), were established in a replicated plot study grazed by cattle in a subtropical environment of the upper North Island of New Zealand. Persistence characteristics were quantified at least five times per annum, over 4 years. Key results: Late-heading cultivars had higher yield, nutritive value, perennial ryegrass content in pasture dry matter, ground cover and tiller density than mid-heading cultivars. There were large seasonal impacts on all ryegrass characteristics, with a major decline over summer and recovery during late autumn into early spring, with less recovery in the final year. Overall, there was a strong linear decline in ryegrass content measured during spring (2018–21). Conclusions: The two late-heading cultivars were more persistent than the two mid-heading cultivars, although persistence declined over 4 years for all cultivars. Implications: Results support industry recommendations of choosing late-heading cultivars for improved pasture quality and persistence. We determined the impact of heading date on persistence of perennial ryegrass cultivars infected with a range of endophytes, in a plot study grazed by cattle. The two late-heading cultivars were more persistent than the two mid-heading cultivars, with higher yield, nutritive value, perennial ryegrass content in pasture dry matter, ground cover and tiller density, although persistence declined over 4 years for all cultivars. [ABSTRACT FROM AUTHOR]

The aphid Aploneura lentisci is widespread in Australia and New Zealand, living all year round on roots of its secondary grass hosts. The fungal endophyte (Epichloë festucae var. lolii), strain AR37 in Lolium perenne is known to greatly reduce populations and was a likely reason for the superior growth and persistence of this association previously observed in the field. Aphid populations were quantified in a field trial near Ballarat, comparing yields of perennial ryegrass infected with eight different endophyte strains and an endophyte-free (Nil) control in a common ryegrass background (Grasslands Samson (G. Samson)). AR37 and another endophyte strain, AR5, had significantly fewer aphids than all other endophytes. These differences were significantly related to yield increases taken before and after sampling that persisted until the end of the trial. In a pot trial comparing commercially available ryegrass-endophyte combinations with equivalent Nil controls, aphid numbers were lower on G. Samson AR37 and Banquet II with AR5 (Endo®5) than on all other cultivar-endophyte combinations. Compared with Nil controls, the common toxic strain in G. Samson, and two strains in Trojan also reduced aphid numbers. The AR5 endophyte produces the alkaloid ergovaline but high concentrations of this in roots of potted plants could not account for differences in root aphid numbers. Root concentrations of epoxyjanthitrems, the only known alkaloids produced by AR37, were low and unlikely to be the cause of resistance to A. lentisci. An aphid, Aploneura lentisci , that feeds on grass roots is widespread in pastures in New Zealand and Australia. This paper reports data confirming that perennial ryegrass infected with a strain of Epichloë fungal endophyte, AR37, is highly resistant to this aphid and shows that another endophyte strain, AR5, gives the same level of control. Suppression of high aphid populations by these endophytes in the field at Ballarat resulted in a 37% increase in pasture production over endophyte-free ryegrass over a 5-month period. [ABSTRACT FROM AUTHOR]

Background: Commercial cultivars of perennial ryegrass infected with selected Epichloë fungal endophytes are highly desirable in certain pastures as the resulting mutualistic association has the capacity to confer agronomic benefits (such as invertebrate pest deterrence) largely due to fungal produced secondary metabolites (e.g., alkaloids). In this study, we investigated T2 segregating populations derived from two independent transformation events expressing diacylglycerol acyltransferase (DGAT) and cysteine oleosin (CO) genes designed to increase foliar lipid and biomass accumulation. These populations were either infected with Epichloë festucae var. lolii strain AR1 or Epichloë sp. LpTG-3 strain AR37 to examine relationships between the introduced trait and the endophytic association. Here we report on experiments designed to investigate if expression of the DGAT + CO trait in foliar tissues of perennial ryegrass could negatively impact the grass-endophyte association and vice versa. Both endophyte and plant characters were measured under controlled environment and field conditions. Results: Expected relative increases in total fatty acids of 17–58% accrued as a result of DGAT + CO expression with no significant difference between the endophyte-infected and non-infected progeny. Hyphal growth in association with DGAT + CO expression appeared normal when compared to control plants in a growth chamber. There was no significant difference in mycelial biomass for both strains AR1 and AR37, however, Epichloë-derived alkaloid concentrations were significantly lower on some occasions in the DGAT + CO plants compared to the corresponding null-segregant progenies, although these remained within the reported range for bioactivity. Conclusions: These results suggest that the mutualistic association formed between perennial ryegrass and selected Epichloë strains does not influence expression of the host DGAT + CO technology, but that endophyte performance may be reduced under some circumstances. Further investigation will now be required to determine the preferred genetic backgrounds for introgression of the DGAT + CO trait in combination with selected endophyte strains, as grass host genetics is a major determinant to the success of the grass-endophyte association in this species. [ABSTRACT FROM AUTHOR]

Aphids are major pests of cereal and pasture grasses throughout the world, vectoring disease and reducing plant production. There are few control options other than insecticides. Epichloë endophytes that produce loline alkaloids in their hosts provide a possible mechanism of control, with both meadow fescue and tall fescue naturally infected with loline-producing endophytes showing a resistance to Rhopalosiphum padi. We screened Elymus spp. naturally infected with endophytes that produced loline alkaloids at concentrations known to affect aphids on fescue but found no effect on these insects infesting Elymus. A synthetic loline-producing endophyte association with rye also had no effect on the aphids. After hypothesizing that the lolines were being translocated in the xylem in Elymus and rye rather than the phloem, we tested the rye and meadow fescue infected with loline-producing endophytes against a xylem feeding spittlebug. The endophyte in rye inhibited the feeding of the insect and reduced its survival, whereas the endophyte-infected meadow fescue had no effect on the spittlebug but reduced the number of aphids. Lolines applied to the potting medium of endophyte-free and endophyte-infected rye, ryegrass, and tall fescue resulted in a decrease in the aphid populations on the endophyte-free pasture grasses relative to the untreated controls but had no effect on aphid numbers on the rye. We tentatively conclude that lolines, produced in both natural and synthetic association with Elymus and rye, are partitioned in the xylem rather than the phloem, where they are inaccessible to aphids. [ABSTRACT FROM AUTHOR]

Water deficit stress largely limits plant growth and survival in natural and managed ecosystems. We studied the morpho-physiological responses of plants associated with distinct strains of Epichloë fungal endophytes to water deficit. We hypothesised that Epichloë symbionts would alleviate the negative effects of water deficit on plants and that both magnitude and mechanisms of endophyte-based alleviation would vary depending on the Epichloë strain. Perennial ryegrass (Lolium perenne) plants from the experimental cultivar GA66 associated with the Epichloë strains AR1, AR5, AR6, and AR37 were subjected to a treatment of sustained water deficit in a pot experiment under controlled growth conditions. We measured plant biomass (shoot and root), water retention, stress-related phytohormones (abscisic acid, jasmonic acid), proline and other water-soluble amino acids, and Epichloë -derived antiherbivore alkaloids. Alleviation of the negative effects of water deficit on plants depended on the Epichloë strain, with AR37 and AR5 providing the greatest protection followed by AR1, while AR6 did not alleviate stress. The AR37-derived water deficit alleviation was associated with enhanced root biomass and plant water retention, and increased concentrations of abscisic acid, proline, and fungal alkaloids. The AR5-derived stress alleviation was associated with enhanced plant water retention and increased proline concentrations, and the AR1-derived alleviation with increased fungal alkaloid concentrations and mycelial biomass. Although AR6 did not alleviate the water deficit, the stress increased Epichloë -derived alkaloid concentrations (and enhanced root biomass) which could provide an advantage for resisting herbivory. Our study highlighted that while Epichloë generally alleviated the effects of water deficit on plants, the mechanisms of stress alleviation varied among associations, and that the host fitness could be increased even in those associations where endophytes did not alleviate direct water deficit stress if herbivores would be present. • Epichloë fungal strains alleviated plant water deficit stress via varied mechanisms. • AR37 increased root biomass, water retention, ABA, proline, and fungal alkaloids. • AR5 increased plant water retention and proline. • AR1 increased fungal alkaloids and mycelial biomass. • AR6 increased root biomass and fungal alkaloids. [ABSTRACT FROM AUTHOR]