The influence of cultural practices on endophyte expression in turf-type tall fescue

Kristina Smith Walker, Purdue University

Abstract

The overall goal in lawn management is sustainability. The utilization of endophytic (E+) tall fescue (Schedonorus phoenix (Scop.) Holub; formally know as Festuca arundinacea Schreb.) may help achieve this goal. Fungal endophytes form a mutulaistic, symbiotic association whereby the plant provides water, nutrients, and structural refuge while the endophyte provides enhanced growth, resistance to drought stress, and protection against surface feeding insect herbivory. Little is known regarding the performance of E+ grasses when cultured under lawn management practices. To maximize the true potential of E+ grasses, it is important to understand how variations in supplemental nitrogen (N) applications and mowing height affect endophyte expression. This series of field, greenhouse and laboratory studies: (i.) determined the seasonal variations in endophyte stem infection levels of a single cultivar and cultivar blend as affected by three annual N regimes (0, 99, and 196 or 0, 123 and 196 kg N ha-1 yr-1), (ii.) determined the effect of mowing height (5 versus 9 cm) and annual N fertility regime (0, 99, and 196 kg N ha-1 yr-1) on endophyte expression as measured by; leaf ergot alkaloid concentrations, plant physiological characteristics, and black cutworm performance (iii.) examined how E+ and non-endophytic (E-) tall fescue and mowing height affected black cutworm performance, and how changes in leaf oxidative enzyme responses from fed leaf tissue vary with insect herbivory, (iv.) determined the effects of various fungicides on stem infection levels when applied during seedling establishment. Seasonal variations in stem infection levels, ranged from 15-43 % and 21-55 % infection for the blend and single cultivar, respectively, with the lowest levels measured in early spring. Infection levels remained relatively stable during the active growing months and supplemental N generally had no effect on infection level. Leaf ergot alkaloid concentrations, ranged from 30 to 4310 ppb, and varied by sampling month, with lower levels measured during late-autumn. Mowing height or N fertility generally did not affect alkaloid concentrations. By contrast, protein and amino-N concentrations increased under high N (196 kg N ha-1 yr-1) whereas sugar concentrations were reduced by high N during some collection months. Black cutworm larval settling response was positively correlated with increasing sugar concentrations for 24 h after introduction. Mowing height and N fertility generally did not impact insect performance, however, mortality was positively correlated with ergot alkaloid concentration and negatively correlated with leaf tissue N content and protein and amino-N concentrations. Endophyte treatment (E+ or E-) and mowing height affected black cutworm settling response and mortality on day seven in which insect mortality was greatest for the E+ treatment mowed at 5 cm. Correlations matrices showed that ergot alkaloids negatively influenced settling response whereas, superoxide dismutase (SOD) and catalase (CAT) activity increased as settling response increased. Commercially available contact or penetrant fungicides generally did not reduce stem infection levels when applied at manufacturer recommended rates. By contrast, propiconazole applied at 2.0 kg a.i. ha-1, twice the label rate, seven days after seedling emergence significantly decreased stem infection. Although mowing height and supplemental N responses were highly variable, in order to maximize E+ tall fescue lawn performance, findings indicate that the turf should be mowed at 9 cm, and fertilized with moderate, 123 kg N ha -1 yr-1, supplemental N. These cultural practices will sustain vigor, positively influence rooting depth, plant physiological characteristics, possibly enhancing host fitness, and equip the plant to protect itself against environmental stresses while also creating a less hospitable environment for insects to settle and feed.

Degree

Ph.D.

Advisors

Bigelow, Purdue University.

Subject Area

Agronomy|Horticulture

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