COMBINING ABILITY FOR PROTEIN DEGRADABILITY IN ALFALFA

The protein in alfalfa (Medicago sativa L.) forage is degraded extensi vely and quickly by ruminant animals, and N may be lost through NH3 fo rmation, Recent research has indicated that the degradability of forag e protein varies among plants, The objective of this study was to dete rmine the relative importance of additive and nonadditive genetic effe cts for protein degradability traits in an alfalfa population derived from major germplasm sources, Eight alfalfa plants were intercrossed i n a half-diallel to produce 28 crossed progenies, Three replications o f the crosses and parental clones were transplanted and grown in Riley County, Kansas, Protein percentages were estimated with microKjedahl, and protein degradability was estimated by degradation with the prote olytic enzyme ficin prior to microKjedahl digestion, Specific (nonaddi tive genetic effects) and general (additive genetic effects) combining abilities were determined for crude and soluble protein, buffer-insol uble and undegradable insoluble protein, and the proportion of undegra dable protein/total insoluble protein, Data for each variable on two h arvest dates in 1993 and 1994 were used in a combined analysis, Harves t date within years was a significant source of variability for all tr aits, A significant genotype effect was detected for all traits except undegradable insoluble protein, General combining ability effects wer e significant for the remaining traits, but specific combining ability effects were significant only for soluble protein. The relative ratio s of additive to nonadditive effects were 0.86 for crude protein, 0.70 for soluble protein, 0.74 for insoluble protein, and 0.80 for proport ion of undegradable insoluble protein/insoluble protein, The results i ndicate that genetic effects for alfalfa protein degradability exist a nd are mostly additive, Recurrent selection procedures should be effec tive in reducing protein degradability in alfalfa.