Morphological trait effects on digestibility of orchardgrass
Fifty orchardgrass (Dactylis glomerata L.) genotypes from two maturity groups were used to investigate relationships between digestibility and morphological traits. Genotypes were selected for blade width, blade length, tiller number, growth habit and seed weight. Plants were harvested from a field planting in spring and summer, and were separated into plant parts before determining in vitro digestible dry matter (IVDDM). Blade width was most consistently associated with IVDDM, with wide-blade genotypes being more digestible than narrow-blade genotypes. Also, stem and blade width were positively correlated with IVDDM. Negative correlation existed between IVDDM and stem length. Differences in digestibility were greatest in stems of reproductive tillers suggesting that stem IVDDM selection may be more important than leaf IVDDM selection for quality improvements;A second study was conducted to determine whether grind size influenced digestion kinetics of orchardgrass selected for divergent morphological traits. Plants from two maturity groups were selected for short, long, narrow, or wide leaf blades. Stems from Spring growth and leaves from regrowth were ground to pass an 8- or 1-mm screen. Digestion lag, potentially digestible cell wall (PDCW) concentration, and digestion rate of PDCW were determined by using a first order, nonlinear model. The results indicate that grinding material through a 1-mm screen did not limit the expression of morphological differences for IVDDM;Anatomical characteristics were examined for narrow- and wide-blade genotypes from two maturity groups. Blade, sheath, and stem samples from Spring growth were collected, fixed, and preserved in formaldehyde-acetic acid-ethanol solution. Samples were embedded in paraffin and stained with safranin to identify lignified cell walls. Total cross sectional area and cross sectional area stained for lignin were quantified by image analysis. Wide-blade clones had the or more lignin in stems than narrow-blade clones, but wide-blade clones had less lignin as a proportion of the cross sectional area than narrow-blade clones. This study shows that differences in digestibility between narrow- and wide-blade clones and between maturity groups may be attributed to variation in lignin deposition.