Abstract
Asexual Epichloë endophytes colonize agricultural forage grasses in a relationship which is mutually beneficial and provides the host plant with protection against herbivorous insects. The endophyte strain AR37 (Epichloë festucae var. lolii) produces epoxy-janthitrem alkaloids and is the only endophyte known to provide ryegrass with resistance against porina larvae (Wiseana cervinata (Walker)), a major pasture pest in cooler areas of New Zealand. This study examined the effect of temperature on concentrations of epoxy-janthitrems in AR37-infected ryegrass and determined how the resulting variations in concentration affected consumption, growth and survival of porina larvae. Twenty replicate pairs of perennial (Lolium perenne L.) and Italian ryegrass (L. multiflorum Lam.) plants with and without endophyte were prepared by cloning, with one of each pair grown at either high (20°C) or low (7°C) temperature. After 10 weeks, herbage on each plant was harvested, divided into leaf and pseudostem, then freeze dried and ground. Leaf and pseudostem material was then incorporated separately into semi-synthetic diets which were fed to porina larvae in a bioassay over 3 weeks. Epoxy-janthitrem concentrations within the plant materials and the semi-synthetic diets were analyzed by high performance liquid chromatography. AR37-infected ryegrass grown at high temperature contained high in planta concentrations of epoxy-janthitrem (30.6 μg/g in leaves and 83.9 μg/g in pseudostems) that had a strong anti-feedant effect on porina larvae when incorporated into their diets, reducing their survival by 25–42% on pseudostems. In comparison, in planta epoxy-janthitrem concentrations in AR37-infected ryegrass grown at low temperature were very low (0.67 μg/g in leaves and 7.4 μg/g in pseudostems) resulting in a small anti-feedant effect in perennial but not in Italian ryegrass. Although alkaloid concentrations were greatly reduced by low temperature this reduction did not occur until after 4 weeks of exposure. Alkaloid concentrations were slightly lower in Italian than in perennial ryegrass and concentrations were higher in the pseudostems when compared with the leaves. In conclusion, epoxy-janthitrems expressed by the AR37 endophyte show strong activity against porina larvae. However, when ryegrass plants are grown at a constant low temperature for an extended period of time in planta epoxy-janthitrem concentrations are greatly reduced and are less effective against this pasture pest.
Highlights
Cool season grasses of the family Poaceae harbour fungal endophytes of the genus Epichloë
When ryegrass was grown at high temperature (HT) epoxy-janthitrem concentrations were greatly increased
Concentrations declined in ryegrass pseudostems grown at low temperature (LT) the decrease was small over the first 4 weeks
Summary
Cool season grasses of the family Poaceae harbour fungal endophytes of the genus Epichloë. Asexual Epichloë endophytes grow as unbranched hyphae within the above ground tissues of the host plant and are transmitted between reproductive generations within the seed of its host. There is an ongoing debate over the nature of the relationship between endophytes and their host (Saikkonen et al, 1998, 2010). The relationship between agricultural forage grasses and asexual Epichloë endophytes, is thought to be defensive mutualistic. The endophyte gains from its host shelter, nutrients and a means of transmission (Saikkonen et al, 2004). In return the plant gains increased protection from biotic stresses including insects (Prestidge et al, 1982; Ball and Prestidge, 1992; Pennell et al, 2005; Popay et al, 2012), mammalian herbivores (Edwards et al, 1993; Cosgrove et al, 2002), pathogens (Panka et al, 2013) and nematodes (Eerens et al, 1997; Bacetty et al, 2009) as well as increased tolerance to abiotic stresses such as drought and nutrient stress (Ravel et al, 1997; Kane, 2011; Nagabhyru et al, 2013)
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