Combining ability and heterotic grouping of elite maize (Zea mays L.) Inbred lines

Abstract

The national average maize yield in Ethiopia is low and thus, choice of promising germplasm, knowledge of combining ability and heterotic grouping are a prerequisites to develop high yielding maize varieties. A line x tester analysis involving 86 test-crosses generated by crossing 43 elite maize inbred lines with two testers and two standard checks were studied for different yield and agronomic traits during 2010 cropping season at Melkasa, Ziway, Dhera, Mieso and Pawe Research Sites. The objectives of the present study were to identify promising test cross hybrid combinations, estimate combining ability of elite maize inbred lines for grain yield and related agronomic traits and classify the inbred lines into different heterotic groups. The genotypes were evaluated in alpha lattice design replicated twice in all the locations. Analyses of variances showed significant mean squares due to genotypes and crosses for most traits in each and across locations. Among the crosses, L23 x T2, L24 x T2, L41 x T1, L23 x T1, L13 x T1 and L17 x T1 showed high grain yield, which could be utilized for future evaluation for possible release or used in maize breeding activities.General combining ability (GCA) mean squares due to lines were highly significant for most studied traits while specific combining ability (SCA) mean squares were significant only for few traits at all locations. The relative importance of GCA and SCA variances observed in the current study for most studied traits revealed the predominance of additive genetic variance in controlling these traits. This suggests that selection would be effective for the improvement of traits of interest. Inbred lines L23, L24 and L41 were the best general combiners for grain yield, and hence were promising parents for hybrids as well as for inclusion in breeding program. Inbred lines L2, L3, L5, L7, L8 and L11 had negative and significant GCA effects for days to anthesis and silking, indicating that the lines had gene combinations that can enhance early maturity. L1, L5, L7, L8 and L37 showed negative and significant GCA effects for plant height in most cases, indicating that these lines had a tendency to decrease plant stature. Crosses L4 x T1, L14 x T1, L22 x T2, L23 x T2, L24 x T2 and L33 x T2 exhibited good specific combining ability effects for grain yield, indicating that the crosses had desirable gene combinations for increased grain yield. Inbred lines L23, L24, L25, L32, L33, and L36 were grouped in to heterotic group A. while inbred lines L7,L13, L14, L17, L25, L27, L29, L30, L34 L41 and L42 were grouped in to heterotic group B. Further studies should explore the possibility of separating the other inbred lines used in this study into distinct heterotic groups using other more divergent testers. In general, the information from this study could be useful for researchers who need to develop high yielding varieties of maize mainly adapted to the rift valley areas of Ethiopia.