Quantitative Inheritance of Forage Quality Traits in Intermediate Wheatgrass

Knowledge of heritability and inheritance of nutritive quality traits in intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey] would be helpful in choosing effective selection techniques. This study assesses variation and heritability of traits associated with hay quality in intermediate wheatgrass, ascertains the relative magnitude of general and specific combining ability (SCA and GCA) for these traits, and examines relationships among important agronomic and quality traits. Six parent clones and the 15 progenies from a diallel cross (reciprocal crosses not included) were evaluated in a replicated field test for in vitro digestible organic matter (IVDOM), neutral detergent fiber (NDF), and N concentration of whole plants, leaf blades, and stems (stem plus leaf sheath). Spike emergence date, plant height, and leaf/stem ratio were also measured. Variation among progenies was significant for all traits except leaf IVDOM and whole-plant N. Leaf/stem ratios varied from 0.22 to 0.28 among progenies, with stems contributing more to whole-plant IVDOM than did leaf blades. Low variation in whole-plant N concentration limits the potential for forage N improvement. Spike emergence date, a measure of relative plant maturity, was correlated positively with IVDOM (r = 0.75**) and negatively with NDF (r = −0.61*). Narrow-sense heritability estimates were moderately high for whole-plant IVDOM and for IVDOM, NDF, and N of stem and leaf fractions. Variance components for GCA were generally higher than those caused by SCA. Year effects for IVDOM and NDF were high, but year × GCA and year × SCA interaction effects for these traits were not significant. Selection for high whole-plant IVDOM in a single environment employing recurrent phenotypic selection or other selection techniques that utilize additive genetic variance should be effective in improving digestibility of intermediate wheatgrass hay.