Combining ability and heterosis for diastatic activity in grain sorghum

Eighty-five sorghum (Sorghum bicolor (L.) Moench) entries including 13 restorer-lines (lines), 5 maintainer-lines (testers), 65 F1 hybrids, and two controls, were grown at Muzarabani, Zimbabwe during the rainy seasons of 1986/87 and 1987/88 to study the combining ability and heterosis for diastatic activity. Grain samples were evaluated for diastatic activity, expressed in Sorghum Diastatic Units (SDU) per gram of malt, in 1989. Differences between sorghum lines, testers, hybrids, and total entries were significant for diastatic activity in both seasons. There were large differences in mean diastatic activity values and ranges for entries in both seasons. The mean SDU g^-1 malt for hybrids varied from 20.5 to 67.2 for the 1986/87 season and 13.3 to 48.9 for the 1987/88 season. Variation in diastatic activity was primarily due to non-additive gene action. The highest positive general combining ability effects were observed for the line 4HA85S, and tester 120A. Significant positive specific combining ability effects were observed for hybrid 120A x D 38073-2. This was the only cross which had positive high parent heterosis in both seasons, but it was only significant in the 1987/88 season. Most of the crosses had negative high parent heterosis. To improve diastatic activity, recurrent selection procedures for specific combining ability should be used to develop elite parents for hybrids.