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Genetic Variability Among Unselected S2 Lines Derived from Four Corn (Zea Mays L.) Composites
Thesis Abstract:
Means, variances, and predicted responses due to selection and correlations among all possible pairs of traits were obtained for nine agronomic traits by evaluating 80 unseleced S2 lines derived from four corn (Zea mays L.) composites, namely: PCI-1, PDC-2, IPB Var. 1, and SUWAN 2. The S2 lines represented random S0 genotypes from the four corn composites.
Highly significant genetic differences (P<0.01) were found among the entries for all traits in each of the four populations except in the case of days before silking which was significant only in IPB Var. 1.
Stand count differences were non-significant only in PDC-2.
Estimates for the line genetic component and, consequently, the predicted gain from selection were quite high for most traits in all four populations. However, the assumption of no dominance and epistatic interaction effects, if present in significant amounts, may have biased the estimates in an upward direction.
The genotypic and phenotypic correlations were estimated for most pairs of traits measured. In most cases, the magnitude of the phenotypic and genotypic correlations were comparable. In cases where differences between the estimates were relatively high, the genotypic correlations were normally of the higher magnitude in all populations except in PDC-2.
Correlations of ear traits with yield are, in most cases, higher than the correlations between plant traits and yield. However, variations as to what ear trait was most highly correlated with yield were observed in the four composites.
Estimates of other genetic parameters such as genetic coefficient of variation, heritability, and correlated response on yield when a secondary trait is selected were also determined for better characterization and comparison of genetic variability in all the traits studied in the four composites.
