Effects of varying ratios of nitrogen, phosphorus and sulfur on Neotyphodium endophyte-mediated resistance in tall fescue (Schedonorus arundinaceus (Schreb.) Dumort)

Although several studies have examined the influence of individual mineral nutrients on the growth, development and anti-herbivore defenses of endophytic grasses, in nature, plants are confronted with complex mixtures of soil nutrients. Resource allocation of turfgrasses may be affected by endophyte infection and the relative proportions of individual nutrients in the soil solution but these factors have not been well studied. Alkaloid concentrations in endophytic plants are known to vary with the availability of soil nutrients which can also alter plant growth and primary and secondary metabolism. By measuring plant, endophyte and insect parameters across different N- P- S nutrient mixtures, this project examines how endophyte infection alters resource allocation in tall fescue. Results may help identify mineral ratios that optimize plant defense and performance while minimizing insect herbivory. To date, results indicate that root biomass (linear model) and amino acid concentrations in above-ground tissue (quadratic model) followed similar patterns across the design space regardless of endophyte infection, whereas different models were required to accurately describe variation in above ground biomass (E+=special cubic model; E-=quadratic model), total soluble plant protein (E+=linear model; E-=quadratic model), and fall armyworm leaf area consumption (E+=full cubic model; E-=overall mean). Fall armyworm survival, water soluble sugars and fructans did not show significant variation in response to the nutrient mixtures, regardless of endophyte infection. In E+ tall fescue, areas of reduced leaf area consumption in the design space could be related to increased concentrations of defensive alkaloids. However, alkaloid data remain to be analyzed.