Combining ability and gene action of four seed yield contributing characters in onion (Allium cepa L.)

For the improvement of onion seed yield mode of gene action is essential to know. Significant D indicated additive variations were greater in magnitude except umbel diameter and significant H1 indicated dominant variation for scape height and umbel diameter. Significant F indicating the presence of dominant genes only in number of umbel. H­2 component is non-significant for all the characters except scape height. Non-significant h2 suggested dominance effect over all loci in the heterozygous phase was not important for number of umbel, scape height and umbel volume. Ratio [(4DH1) 1/2 + F] / [(4DH1) 1/2 – F] is greater than one for umbel volume indicated presence of an excess of dominant genes in the parents. For all the characters, ratio h2/H2 smaller than one indicated the involvement of at least one group of dominant genes. Parent P4 observed as good general combiner, F1 (P3 ´ P4, P1 ´ P2, P1 ´ P4, P1 × P5 and P1 × P3) and reciprocal crosses (P2 ´ P1, P3 ´ P1 and P4 ´ P1) for different traits recorded as the good specific combiners. So, this parent, F1 and reciprocal crosses need to special consideration for the improvement of onion yield.