Estimation of Acremonium Coenophialum Mycelium in Infected Tall Fescue
- C. A. Roberts,
- F. E. Barton and
- K. J. Moore *
Current methods for assessing the infection level in tall fescue (Festuca arundinacea Schreb.) infected with the fungal endophyte, Acremonium coenophialum Morgan-Jones & Gams, do not quantify mycelial dry matter. The objective of this study was the estimation of mycelium by chemical and spectral determination of chitin, a fungal cell wall polymer. Tall fescue samples with various proportions of infected plants were collected from paddocks established on a Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludult) soil. Samples were analyzed for chitin, and the chemical data were used to develop a spectral prediction equation using near infrared spectroscopy (NIRS). The calibration and validation coefficients of determination were 0.86 and 0.84, respectively. The validated equation was used in the prediction of chitin in 95 other samples collected from paddocks microscopically evaluated for percent infected plants, and microscopic data were regressed against predicted chitin. Percent infection, as predicted by the microscopic procedure, and chitin concentration were not correlated (P > 0.05). The NIRS calibration set was expanded to include samples collected in Illinois. The improved equation accounted for 91 and 89% of the variability in calibration and validation, respectively. The mean and standard error of calibration were 328 and 50 mg kg−1 dry matter (DM), respectively. The expanded equation was used to quantify chitin from spring and fall pastures in Illinois that contained 100% infected plants. Chitin in spring pastures ranged from 118 to 961 mg kg−1 DM and varied greatly. Fall chitin varied little and the maximum concentration was 596 mg kg−1 DM. We concluded that endophytic chitin in tall fescue could be quantified chemically and spectrally. If potential sources of error are accounted for, these procedures can be used to estimate relative A. coenophialum mycelium.
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