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Prediction of Cell Wall Carbohydrates and Quality in Panicum Species by Near Infrared Reflectance Spectroscopy

Plant Physiology Div., DSIR, Palmerston North, New Zealand;
USDA-ARS and Dep. of Crop Science North Carolina State Univ., Raleigh, NC 27650
Dep. of Biological and Agricultural Engineering North Carolina State Univ., Raleigh, NC 27650
Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27650.

^* Corresponding author.

The composition of forage plant cell walls alters the rate and extent of dry matter digestion. A rapid, nondestructive method of analysis that avoids constituent rearrangements and artifact formation would aid the ease and accuracy of determining the structural carbohydrates (SC). This study evaluated the use of near infrared reflectance spectroscopy (NIRS) for predicting the SC fractions and constituent carbohydrate monomers the cell walls of whole and separated plant parts of subtropical grasses. Two accessions representing a high and low in vitro dry matter disappearance (IVDMD) were selected from within three Panicum taxa [Panicum amarum Elliot var. amarum, P. amarum var. amarulum (Hitch. and Chase) P.G. Palmer, and P . virgatum L.] that had been classified morphologically into tall (hay), intermediate, and short (grazing) categories. Variation occurred in SC duet o morphology, maturity, plant part (leaf blade, leaf sheath, and stem) and in IVDMD. Cell wall xylose from trifluoroacetic acid hydrolysis was predicted by NIRS with relative accuracy (R² = 0.91 for calibration, r = 0.88 for prediction) and with standard errors for calibration and analysis of 10.2 and 15.9 g kg^–1, respectively. Predicted values for cell wall xylose concentrations of equivalent samples (n = 30) from two successive years compared very closely, with only small changes in relative ranking between years (r = 0.92). Similar results were noted for arabinose (r = 0.78), galactose (r = 0.80), glucose (r = 0.79), and quality variables such as IVDMD, neutral detergent fiber, and acid detergent fiber (r = 0.91). Composition of cell walls using NIRS technology may provide a physiological base for the genetic improvement of low quality forage grasses, especially the xylose concentration, which is known to be inversely related to IVDMD.

Key Words: Arabinose • Xylose • Galactose • Glucose • In vitro dry matter disappearance • Neutral detergent fiber • Acid detergent fiber • Trifluoroacetic acid hydrolysis

Received for publication June 15, 1987.