A diallel cross from eight late maturing maize, zea mays L., inbreds was used to determine general, specific and reciprocal combining ability in the seed & Plant Improvement Institute fields in karaj during 1988-1989. Eight maize inbred lines including B73, K86, K98, K104 (from dent group) and K583, K2814 (from flint group) were crossed in a diallel model with all possible combinations including reciprocals in the first years. Seeds of these inbred lines a long with those of all the main as well as the reciprocal crosses were planted in a simple lattice design with two replication in the second year.
Eight characters including plant height (Cm), yield per plant (gr), kernel row number, kernel number per row, ear cob content (%), 1000-kernel weight (gr), protein content (%) and oil content (%) were measured and studied.
The analysis of variance for the simple lattice design showed the significant differences amony the treatments for all the characters in 1989. The randomized complete block design (where Eb<Ee) were conducted for two of the above mentioned characters.
Griffing (method 1, model 1) procedure was used to partition genetic variation and to estimate the combining ability and heterosis. Mean square values for general, specific and reciprocal combining ability (gac, sca & rca) were found to be highly significant (P=0.01) for all the traits studied.
The variance ratio for combining ability (gca/sca) calculated for all traits and showed non-additive gene effects for plant height and yield per plant, but additive effects for other traits. In general B73 and K104 lines were the best general combiner almost for all traits.
The sca values for all the characters were highly significant (P=0.01). The B73 line was the best one in showing most significant sca is for different characters.
The hybrid, "K583× K98" was the best on for high yielding ability.
Simple correlation coefficients between traits for both hybrids and lines showed that in parents plants height, 1000-kernel weight and kernel per row were positively correlated with yield. However, correlation coefficients between other traits were non significant with yield. However, correlation coefficients between other traits were non significant with yield.
Yield per plant, plant height, kernel per row and 1000-kernel weight showed the highest rate of heterosis, which are 54, 24, 18 and 16 percent respectively. Although the "rca" values were significant for some of the observation, but the cytoplasmic or material effects were not considerable for any trait.