Abstract
The effect of inbreeding depression on forage yield in alfalfa (Medicago sativa L.) was determined with nineteen clones, which had been improved in agronomic traits at the Hokkaido National Agricultural experiment Station. the yield of S_1 progenies of parental clones relative to that of their respective F_1 progenies (YS_1/F_1) averaged 83.9%. There were positive correlations between allelic interaction effect and specific combining ability effect or yield of F_1 progenies, indicating that the yield of clones and their F_1 progenies are affected by the multiple allelic interaction. On the other hand, these clones differed greatly in response to selfing, with YS_1/F_1 ranging from 58.7 to 111.6%. A few clones produced S_1 progenies which outyielded the average of their respecsive F_1 progenies, suggesting the contribution of favorable additive effect of alleles to the increase in yield. These results indicate that, in practical breeding program of alfalfa, selection for yield results in increase in heterozygosity and accumulation of favorable additive effect and that clones do not respond similarly to inbreeding. It is concluded that the determination of relative effectiveness of increasing heterozygosity and accumulation favorable additive effect is prerequisite for maxmizing combining ability of alfalfa.
