Six extra-early quality protein maize (QPM) inbred lines from IITA were investigated using a partial diallel cross design. The objectives were to assess the hybrids and their parents for their agronomic performance. The six parents along with their hybrids (15) were evaluated using a Randomized Complete Block Design (RCBD) with three replications per site in four locations. General combining ability (GCA) and specific combining ability (SCA) effects as well as mid-parent heterosis were determined. Results of combined analysis of variance (ANOVA) revealed significant environmental effect for all the traits studied. Significant additive effect was observed for only grain yield whilst non-significant GCA and SCA effects were identified for all other traits. The GCA estimate identified parental lines P1, P3 and P5 as the high combiners for grain yield. The GCA estimates identified parental lines P1, P3 and P5 as the best combiners for grain yield. Again, P1 was the most suitable parent for increased cob length, cob diameter, number of rows per cob and reduced anthesis-silking interval; P3 for thousand-grain weight and reduced days to flowering (anthesis and silking days), and P5 for number of kernels per row, and reduced plant height and ear height. Hence, these parents may be used in hybridization programmes as donors of the superior traits indicated. The highest values for SCA and mid-parent heterosis for grain yield were observed in the crosses P1xP4, P5xP6, P1xP5 and P4xP6.
Key words: Quality protein maize (QPM), diallel, combining ability.