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Genetic Variability in Acid Detergent Fiber, Crude Protein, and Their Association with Some Morphological Characters in Smooth Bromegrass¹

A seven x seven half diallel of smooth bromegrass Bromus inermis Leyss., including parental clones, was evaluated for acid detergent fiber (ADF) and crude protein (CP) of whole forage at two harvests and of leafblade, leaf-sheath, and stem sampled before the first harvest. The objectives were to assess the genetic variability for the quality components, and to examine the associations between the two quality components and some morphological characters.

The relative magnitude of the variances due to general and specific combining ability indicated that most of the genetic variance appeared to be nonadditive. Neither ADF nor CP showed significant combining ability at the second harvest. The narrow-sense heritability estimates were quite high for ADF of the leaf-blade (46%) but were very low for ADF and CP of whole forages at both harvests (3 to 8%) and for ADF of other plant fractions (0 to 19%). The nature of the genetic variances for ADF and CP suggested that more complicated breeding methods would be necessary for quality improvement.

Acid detergent fiber of the leaf-sheath and stem was closely associated with whole forage ADF (r = 0.70 and 0.84). High correlations were obtained between harvests for both ADF and CP (r = 0.71 and 0.61). ADF increased while CP decreased with increasing plant height and forage yield. Vein frequency was positively correlated with ADF of whole forage (r = 0.41) and leaf-sheath (r = 0.51). Most phenotypic characters showed little correlation with either ADF or CP at the first harvest.

Key Words: Diallel • General combining ability • Specific combining ability • Heritability • Forage quality

² Graduate research assistant, alfalfa breeder and chairman, Plant Science Dep., Univ. of Alberta, Edmonton, Alberta, Canada. T6G 2E3.

Received for publication March 29, 1977.