COMBINING ABILITY VARIATION OF OSMOTIC ADJUSTMENT AMONG A SELECTED RANGE OF GRAIN-SORGHUM (SORGHUM-BICOLOR L-MOENCH) LINES

Osmotic adjustment has been widely proposed as a plant attribute that confers adaptation to water stress. Genetic variation for osmotic adju stment among ten inbred sorghum lines was investigated by diallel anal ysis. Both general combining ability (GCA) and specific combining abil ity (SCA) were found to be significant (P < 0.05). The differences in patterns of GCA and SCA among the parents provided strong evidence tha t genetic variation for osmotic adjustment among the ten parents was c ontrolled by more than one gene. Four parents (TAM422, Tx2813, Ajebsid o and 40019), which phenotypically expressed high osmotic adjustment, expressed different patterns of GCA and SCA. This suggests that the ge netic control for high osmotic adjustment differed among the four pare nts. Two major patterns of combining ability inheritance were identifi ed among the high osmotic adjustment parents, one of these based on po sitive GCA inheritance (TAM422 and 40019) and the other on negative GC A inheritance (Tx2813 and Ajebsido). However, SCA influenced the expre ssion of these patterns of inheritance and their expression was modifi ed in specific parental combinations.