Effects of Neotyphodium coenophialum on plant-insect interactions in tall fescue (Schedonorus arundinaceous (Schreb.) Dumort) as affected by various ratios of nitrogen, phosphorus and sulfur
Abstract
Fungal endophytes in the genus Neotyphodium are symbionts of several important turf and forage grasses. They depend on their grass mutualist mainly for nutrition while providing the plant with enhanced growth, tolerance to environmental stress and resistance against insect herbivory. The basis for insect resistance lies in the synthesis of several alkaloids that can negatively affect insect performance. Although the effects of independent nutrients on the dynamics of Neotyphodium-grass interactions have been studied, nutrient balance and effects stemming from interactions between nutrients have not been examined. I evaluated endophytic (E+) and non-endophytic (E-) tall fescue growth and primary metabolism, fall armyworm (FAW) performance and alkaloid production (only on E+ tall fescue) across a nutrient space represented by different eleven nutrient mixtures containing varying ratios of nitrogen (N), phosphorus (P) and sulfur (S). The objectives were to 1) test the mineral balance hypothesis in endophyte-infected (E+) and uninfected (E-) tall fescue and identify N, P and S ratios representing optimal nutrient balance blends; those areas within the nutrient space that provide high above- and below-ground biomass, reduced insect feeding and survival (for both E- and E+) and relatively high levels of endophyte-mediated defensive alkaloids (E+ tall fescue only); 2) describe the role of endophyte infection in determining the N:P:S ratios that provide optimal plant growth and reduced fall armyworm performance on tall fescue. Results indicated that mineral mixtures with high N and low P and S ratios resulted in highly desirable outcomes for both E- and E+ tall fescue. Mixtures with relatively low N ratios (50%) also yielded highly desirable outcomes for E+ tall fescue. Endophyte infection can significantly alter how plants respond to varying nutrient resources and these responses are complex and heavily dependent on interactions between mineral nutrients. Findings herein indicate potentially important differences in the fertility requirements of tall fescue based on the endophyte infection status of the plant and imply that infection may broaden the range of soil nutrient conditions that result in desirable ecological outcomes for the plant.
Degree
Ph.D.
Advisors
Richmond, Purdue University.
Subject Area
Plant biology|Ecology|Entomology
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