Genetics and Genetic Response in Populations Generated from Two Cycles of Phenotypic Mass Selection in Sweet Corn (Zea Mays L. Saccharata)
Ali, Eltahir Siddig (2003) Genetics and Genetic Response in Populations Generated from Two Cycles of Phenotypic Mass Selection in Sweet Corn (Zea Mays L. Saccharata). PhD thesis, Universiti Putra Malaysia.
Local composite varieties of sweet com (lea mays L. saccharata) offer moderate yields and eating quality, while imported hybrid varieties are less adaptable to the local environment, although having good eating quality. A breeding programme was therefore initiated at Universiti Putra Malaysia (UPM). utilising both genetic materials to produce new superior genotypes. The main objectives of this study were to investigate the genetics of populations, and to evaluate genetic response in two sweet com populations generated from two cycles of phenotypic mass selection. In Experiment 1, a local cotnposite variety, Manis Madu and two imported hybrid varieties, Hybrid SSC 240 and Hybrid 368 were first evaluated, and found to show comparable performance. Consequently, Manis Madu and Hybrid SSC 240 were chosen as source populations for selection and were then crossed to generate the base population. In Experiment 2, the performance of the cross population was compared to its parents, and was found to show more resemblance to Hybrid SSC 240. Separately and simultaneously, two cycles of phenotypic mass selection for ear length were employed on the two base populations, Manis Madu, designated as M CO, and the intennated crossed population, designated as MS CO, at Field 2, UPM. The two base populations and the populations generated from the two cycles of selection were then evaluated and compared for general performance at two locations, Field 2 and Share Farm, in UPM. In Manis Madu populations (M), the predicted responses to individual cycles of selection were almost the same for both cycles, 19.3% in the first cycle and 19.6% in the second. The cumulative predicted response in M C2 population was 43.6%. In the cross populations (MS), the predicted response to individual cycles of selection was higher in the second cycle (26.5%) than it was in the first (16.8%). The cumulative pred icted response in MS C2 population was 46.4%. The two populations responded differently to the two cycles of selection, where, in Manis Madu populations, a positive realised response was only attained in first cycle (4.1%), while a negative one was observed in the second (-0.7%). In contrast, the cross populations showed negative realised response in the first cycle (-0.7%), while a reasonable positive one (2.08%) was observed in the second. The average cumulative realised response to selection was higher in M C2 (3.4%) than that in MS C2 0.4%). As expected, the realized responses were lower than the predicted.
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