A Tale of Two Grass Species: Temperature Affects the Symbiosis of a Mutualistic Epichloë Endophyte in Both Tall Fescue and Perennial Ryegrass

Abstract

Many cool-season grasses form permanent, mutualistic symbioses with asexual Epichloë endophytes. These fungal symbionts often perform a protective role within the association as many strains produce secondary metabolites that deter certain mammalian and invertebrate herbivores. Although initially a serious issue for agriculture, due to mammalian toxins that manifested in major animal health issues, selected strains that provide abiotic stress protection to plants with minimal ill effects to livestock are now commercialized and routinely used to enhance pasture performance in many farming systems. These fungal endophytes and their grass hosts have coevolved over millions of years, and it is now generally accepted that most taxonomic groupings of Epichloë are confined to forming compatible associations (i.e., symptomless associations) with related grass genera within a tribe. The most desired compounds associated with Epichloë festucae var. lolii, an endophyte species associated with perennial ryegrass, are peramine and epoxy-janthitrems. No other major secondary metabolites with invertebrate bioactivity have been identified within this association. However, other agriculturally beneficial compounds, such as lolines, have been discovered in related endophyte species that form associations with fescue grasses. A rationale therefore existed to develop novel grass-endophyte associations between loline-producing endophytes originally isolated from tall fescue with elite cultivars of perennial ryegrass to achieve a wider spectrum of insect bioactivity. A suitable loline-producing endophyte strain of Epichloë sp. FaTG-3 was selected and inoculated into perennial ryegrass. We hypothesed that endophyte transmission frequency, endophyte mycelial biomass and endophyte-derived alkaloid production would differ between the original tall fescue host and the artificial association. Consistent with our hypothesis, our data strongly suggest that plant species significantly affected the plant-endophyte association. This effect became more apparent for transmission frequency and endophyte biomass as the plants matured. Overall, the viable endophyte infection frequency was greater in

Interaction between Grasses and Epichloë Endophytes and Its Significance to Biotic and Abiotic Stress Tolerance and the Rhizosphere

“…Endophyteinfected (E + ) grasses have been documented to gain protection from drought, insects, nematodes, cold, flooding, heavy metals, pathogens, and mammalian herbivory [19]. Loline and peramine alkaloids are known insect deterrents and insecticides [20,21]. Ergot alkaloids and indole-diterpenes alkaloids have mammalian toxicity properties as well as some insect protection [13].…”

Interaction Between Grasses and <em>Epichloe</em> Endophytes and Its Significance to Biotic and Abiotic Stress Tolerance and the Rhi-Zosphere

“…Seeds exposed to hot, humid weather for an extended period can lose their endophyte. Very cold weather may affect fungal transmission to the grass progeny [20]. Temperature can also influence individual alkaloid production [37] and soil nutrients can influence endophyte infection.…”

“…drought, insects, nematodes, cold, flooding, heavy metals, pathogens, and mammalian herbivory [19]. Loline and peramine alkaloids are known insect deterrents and insecticides [20] [21]. Ergot alkaloids and indole-diterpenes alkaloids have mammalian toxicity properties as well as some insect protection [22].…”

“…However, endophyte-infected host grasses do not produce these responses against the endophyte. The endophyte lives and grows in the intercellular space within the plant, in synchrony with the plant maturation [20]. The fact that the plant does not react to the endophyte as a pathogen, and that the endophyte only grows in pace with the grass suggests significant cross-talk between the two species.…”

Fungal Endophytes Promote Tomato Growth and Enhance Drought and Salt Tolerance

“…Lifestyle switching occurs in such genetically divergent plants such as the cucurbitaceous and solanaceous families, as well as in their cultivars, e.g., tomato (Solanum lycopersicum) [25]. In addition, the occurrence of endophytes in natural grass populations positively correlates with water stress [26][27][28][29][30].…”