Genetic Diversity and Combining Ability in Maize (Zea mays L.)

Abstract

The present study was carried out during 2008/2009, 2009/2010 and 2010/2011 to obtain information about the performance of maize inbred lines, genetic diversity, gene action and assessment of the combining ability of parental lines and their F1s by using diallel fashion. Genetic variability analysis revealed that days to maturity, plant height and number of rows/cob had higher variability, heritability and genetic advance in percentage of mean. Broad-sense heritability estimates of the characters were higher in magnitude (66.08 to 93.41%) indicating greater genetic impact on these characters. Positive significant phenotypic and genotypic correlations were found for days to maturity, number of kernels/row and number of grains/cob. The path analysis revealed that number of rows/cob, cob length and number of kernels/row had the highest direct effect on grain yield, while plant height and ear height and number of grains/cob had the highest moderate indirect negative effects on grain yield. Selection indices were constructed through the discriminate function using nine characters. From the results, the highest relative efficiency was observed with the selection index based on four characters viz., ear height, number of rows/cob, number of kernels/row and grain yield/plant. Cob length, number of kernels/row and number of grains/cob could be the important selection criteria in the improvement of maize lines and hybrids for higher grain yield. The average inter-cluster was always higher than the average intra-cluster distance suggesting wider genetic diversity among the inbred lines of the groups. Cluster III had the highest intra and inter-cluster distance was maximum between clusters I and II. So, the inbred lines chosen from these clusters would give broad spectrum of variability in the segregating generation. A half diallel set of six maize inbred lines were utilized to evaluate combining ability and heterosis for yield and its components characters. General and specific combining ability effects were significantly different among the parental lines. The parents P5 and P4 were considered suitable according to their yield capacities and general combining ability effects. The variances for general (gca) and specific (sca) combining ability for plant height, cob diameter and number of rows/cob were highly significant indicating the presence of additive as well as non-additive gene effects for controlling the characters. In the present study the values of F for all the characters except cob diameter were positive and greater than zero, which expressed that dominant alleles were more frequent than recessive alleles. The estimate of additive genetic variance (D) was significant for days to silking, days to maturity, ear height and number of rows/cob indicating the importance of additive gene effect in their inheritance. Thus highly significant values of the components D, H1 and H2 indicated the importance of both additive and dominant gene effect for the characters under study. The ratio of [4DH1)½ +F]/[4DH1)½-F] estimates the relative proportion of dominant and recessive alleles in the parents. From Wr-Vr graph it has been noticed that expression of dominant and recessive alleles in the parents was influenced by environment as the same parent showed different positions on graphs. From this study, it is concluded that parents with recessive and dominant genes can also contribute towards high yield. The mid parent heterosis values ranged from 1.73% (P1×P6) to 5.21% (P1×P2) whereas, the useful heterosis values varied between-40.36% (P1×P5) and 4.94% (P1×P2), and only five crosses had higher grain yield. Of these crosses, P1×P2, P2×P5, P4×P5 and P5×P6 were considered promising hybrids and will be tested in yield trials for further evaluation. Taking the lines of these promising crosses into account, parents P5 and P4 may be used as parents in hybrid maize programs. In addition to these parents, P3 with dominant genes, high yield and general combining ability may be recommended as another parent.