Theses and Dissertations
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Theses and Dissertations (Department of Plant and Science)
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Browsing Theses and Dissertations by Author "Fakorede, M. A. B."
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- ItemOpen AccessGenetic Variability and Predicted Responses to Four Types of Progeny Selection in a Nigeria Maize (Zeamays L.) population.(Obafemi Awolowo University, 1986) Adeyemo, Moses Olusegun; Fakorede, M. A. B.Genetic variability and predicted responses to full-sib (FS), half-sib (HS), Si and S1 testcross (TCH) selection methods were studied in the open-pollinating maize variety, TZSR-Y-1. Evaluation of progress after one cycle of selection was also done. Grain yield and seven agronomic traits were investigated. Mean grain yield ranged from 3.4 to 9.2 t/ha for FS, 2.9 to 7.5 t/ha for HS, 1.75 to 8.0 t/ha for S1 and 3.2 to 8.8 t/ha for TCH. Genetic variances ( 4;2) were largest for S1 families but there were no consistent trends for c2 among the other progeny types. Additive genetic variance constituted- the major portion of the total genetic variance for grain yield and the agronomic traits. Heritability estimates were moderate to high for nearly all agronomic traits of the four progeny types. Generally, only the correlations of yield with ear number per plot and ear length had coefficients appreciably larger than 0.50; these two traits were therefore the primary determinants of grain yield. Largest predicted direct gain per season of selection for grain yield was obtained for S1 families followed by TCH and FS which differed little. HS selection gave the smallest predicted gain. Predicted correlated responses in grain yield assuming selection was done for agronomic traits were generally smaller than predicted direct responses to selection for grain yield. After one cycle of selection, yield improvements of the derived populations relative to the source population were -2.5% for SI, 8.8% for HS, 13.5% for FS, and 14.6% for TCH selection methods. On the basis of operational efficiency and predicted versus realized gains from selection, FS family selection would be more effective than the other selection methods studied for improving the maize variety TZSR-Y-1.
- ItemOpen AccessGenotype X Environment Component of Variance and its Implications in Maize (Zeamays L.) Yield Trials.(Obafemi Awolowo University, 1985) Adisa, Aramide Omolara; Fakorede, M. A. B.Grain yield data obtained from yield trials conducted in 1981 and 1982 for five open-pollinating cultivars and eight varietal hybrids of maize (Zea mays L.) were used to investigate the effectiveness of 3 different yield trial methods. These included experiments A: 2 years, 2 locations, 1 planting date; experiment B: 1 year, 2 locations, 3 planting dates, and experiment C: 2 years, 1 location, 3 planting dates. Variance components were obtained for each method and optimum combinations of numbers of years, locations, planting dates and replications for varietal testing were determined by calculating theoretical standard error of the mean (SEM). Analysis of variance for the three methods showed highly significant location, year, planting date and genotype effects. SEM of 0.256 was obtained for 2 years, 2 locations, 1 planting date and 4 replications, and this was used as the standard for comparing the other two methods. When planting dates were substituted for years in experiment B, the SEM of 0.256 was obtained for combinations ranging from 1 year, 8 locations, 2 planting dates and 1 replication, to 1 year, 2 locations, 2 planting dates, and 4 replications. Substituting planting dates for location in experiment C however, resulted in the use of a larger number of planting dates than in experiment B, and not less than a 1-year period of testing to obtain the minimum SEM of 0.256. Planting dates can therefore be effectively substituted for years in order to reduce the time for conducting preliminary maize yield trials. Planting dates can also be substituted for locations where funds but not time, are limiting.
- ItemOpen AccessInheritance of Yield and Agronomic Traits in a Maize (Zeamays L.) Population at Two Levels of Inbreeding.(Obafemi Awolowo University, 1986) Ajala, Samson Oyewole; Fakorede, M. A. B.Hybrids resulting from diallel crosses of ten radom lines at the second (S2) and fifth (S5) generations of inbreeding in the TZSR-W population of maize (Zea mays L.) were studied. Eight of the lines were common to both generations. At both generations, general combining ability (gca) was more important than specific combining ability (sca) for most traits. For grain yield however, gca and sca were nearly equal. Therefore, recurrent selection methods that utilize both additive and non-additive gene actions should be used to improve the population. Generally, lines with positive gca effects at the S2 generation also had positive gca at the S5 generation with line 013 being the best at both generations. However, the relative performance of crosses (sca) differed between the two generations. Appreciable inbreeding depression had occurred at the S2 generation with little further depression at the S5 generation. The preponderance and relative stability of gca effects, and the magnitude of inbreeding depression at the S2 generation suggest that good inbred lines can be selected as from the S2 generation. However, the inconsistent ranking of hybrids for sca effects at both generations implies that the yielding ability of such selected lines must be specifically tested to identify the best hybrid combinations. Correlation, stepwise multiple regression and path-coefficient analyses indicated that vigorous lines that mature early, with long rather than wide ears will be high-yielding in hybrid combinations. These analyses also showed that shelling percentage, emergence percentage and numbers of days to silking of S2 X S2 hybrids positively influenced grain yield in the S5 X S5 hybrids. Therefore, these traits could be used as indirect selection criteria for high-yielding hybrids.