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 adjustment among ten inbred sorghum lines was investigated by diallel analysis. Both general combining ability (GCA) and specific combining ability (SCA) were found to be significant (P < 0.05). The differences in patterns of GCA and SCA among the parents provided strong evidence that genetic variation for osmotic adjustment among the ten parents was controlled by more than one gene. Four parents (TAM422, Tx2813, Ajebsido and 40019), which phenotypically expressed high osmotic adjustment, expressed different patterns of GCA and SCA. This suggests that the genetic control for high osmotic adjustment differed among the four parents. Two major patterns of combining ability inheritance were identified among the high osmotic adjustment parents, one of these based on positive GCA inheritance (TAM422 and 40019) and the other on negative GCA inheritance (Tx2813 and Ajebsido). However, SCA influenced the expression of these patterns of inheritance and their expression was modified in specific parental combinations.