Wound induced resistance in endophyte infected Tall fescue.
Sullivan, Terrence*,1, Bultman, Thomas1, Rodstrom, John1, Van Dop, Joshua1, Librizzi, James1, Graham, Candace1, 1 Department of Biology, Holland, MI
ABSTRACT- Cool season grasses are commonly infected by fungal endophytes from the genus Neotyphodium. This interaction can be mutualistic as Neotyphodium endophytes can provide their hosts with variety of benefits including increased nutrient uptake, drought resistance and defense against both vertebrate and invertebrate herbivores. Herbivore defense is accomplished via the synthesis of alkaloids, although alkaloid production by Neotyphodium endophytes can be highly variable and conditional on both genetic and environmental factors. One environmental factor that can influence alkaloid production is prior damage to its host. In a previous experiment, a significant negative effect was found on Rhopalosiphium padi (bird cherry-oat aphid) when they were raised on new growth of Neotyphodium infected Festuca arundinacea (tall fescue) plants that had been previously cut to simulate vertebrate grazing. In this experiment, we tested the hypothesis that invertebrate herbivory can also affect chemical defenses provided by Neotyphodium. F. arundinacea carrying Neotyphodium coenophilium (E+) and endophyte-free F. arundinacea (E-) were damaged 6 weeks after germination either by herbivory by Spodoptera frugiperda (fall army worm) or by cutting. Two weeks after damage the aphid R. padi was used as a bioassay. As expected, aphid reproduction was reduced on E+ hosts regardless of treatment. There was a significant interaction between endophyte status and damage. Damaged E+ plants had increased resistance to aphids relative to control plants while damaged E- plants were more susceptible than controls. We also examined the mechanism for these changes by assaying levels of mRNA expression for two loline synthesis genes via real-time RT-PCR and by assaying the concentration of lolines via HPLC.
Key words: endophytes, Neotyphodium, Festuca arundinacea, induced defenses
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.