Abstract

Castor (Ricinus communis L.) is one of the world’s most important non-edible oil seed crops and is indigenous to eastern Africa. Estimates of heterosis and combining ability help identify parents with better-combining abilities, which may be hybridized to produce elite crosses. This paper aims to estimate the magnitude of heterosis and combining ability in castor for yield and yield-related traits. A total of 28 entries (twenty-one crosses generated in a half-diallel mating design and seven parents) were planted in three replications of RCBD at the Melkassa Agricultural Research Center and Negelle Arsi sub-centers. Separate mean square analysis due to total genotypes, parents, crosses, and parent vs crosses for yield and yield contributing characters indicated significant differences for all of the studied traits except 100-seed weight, number of branches per plant, and female inflorescence length for parent vs crosses contrast, suggesting there was considerable genetic variation among materials studied. Combining ability analysis for general (GCA) and specific (SCA) was very highly significant (P <0.001) for all traits, indicating the importance of both additive and non-additive gene action in controlling the expression of traits. The high yielder and dwarf genotype MD-1 was the best general combiner for most yield- and yield-related traits, followed by genotype M-5/Sel-1. Five crosses, MD-1 x M-5/Sel-1 (6.03***), Hiruy x M- 5/Se-1 (5.23***), 106552 x 21936/1 (4.54***), Hiruy x 21936/1 (3.83**) and MD-1 x 208630 (2.92*), exhibited good specific cross combinations for biological seed yield. For 100-seed weight, MD-1 x 208630 and M-5/Sel-1 x 21936/1 crosses expressed significant effects for good specific combinations. The wide range of standard heterosis recorded for seed yield varied from -45.68 to 86.13% over Hiruy and -52.81 to 61.71% over Abaro. Three hybrids, MD-1 x 208630, MD-1 x M-5/Sel-1, and Hiruy x M-5/Se-1, manifested high standard heterosis over both Hiruy and Abaro for total seed yield of commercial value. Estimated heterosis for seed yield ranged from 52.81 to 57.02% for the better parent; and - 45.05 to 65.06% for mid-parent heterosis. The information generated in this study can be used to develop castor hybrids with high seed yields