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Stability and Relative Importance of General and Specific Combining Ability for Forage Yield in Orchardgrass¹

The objectives of this research were to evaluate the relative importance of general (GCA) and specific combining ability (SCA) for forage yield in orchardgrass (Dactylis glomerata L.) and determine if more nearly consistent results could be obtained by separating GCA and SCA into components associated with annually recurring changes and changes related to age of stand. For this purpose, seeded plots of hybrids from six diallel crosses involving 11 parental clones were harvested 28 times during a 5-year period (4th year excluded).

GCA was significant for most harvests, seasons, and years, and for total 4-year production. SCA was significant for spring and annual production of the first 2 years. Interactions of GCA with seasons and of SCA with years were significant. Interseasonal correlation coefficients based on total 4-year production for spring vs. summer, spring vs. fall, and summer vs. fall, respectively, were 0.25, 0.45, and 0.58 for GCA effects, and 0.64, 0.19, and 0.63 for SCA effects. Interannual correlation coefficients based on annual yields in consecutive years (excluding 1967) starting with 1964–1965 were – 0.16, 0.45, 0.65 for GCA effects and 0.42, 0.38, and – 0.18 for SCA effects.

The data suggested an annual recurrence of relative seasonal magnitudes of GCA and SCA with interannual stability increasing for GCA and decreasing for SCA as the stand aged. Most effective selection for forage production based on GCA probably would be on a seasonal basis in the 3rd year after seeding. Selection based on SCA appears questionable, although it might be successful for initial spring production.

Key Words: Dactylis glomerta L. • Diallel

² Associate professor of agronomy and soils, Clemson Univ., Clemson, SC 29631.

Received for publication January 30, 1980.