Fingerprinting of Zimbabwean maize hybrids and some elite lines to study heterotic patterns and genetic diversity for gray leaf spot resistance

Chigeza, Godfree (2003). Fingerprinting of Zimbabwean maize hybrids and some elite lines to study heterotic patterns and genetic diversity for gray leaf spot resistance MPhil Thesis, School of Land, Crop and Food Sciences, The University of Queensland.

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Author Chigeza, Godfree
Thesis Title Fingerprinting of Zimbabwean maize hybrids and some elite lines to study heterotic patterns and genetic diversity for gray leaf spot resistance
School, Centre or Institute School of Land, Crop and Food Sciences
Institution The University of Queensland
Publication date 2003
Thesis type MPhil Thesis
Supervisor Dr Ian Godwdn
Dr Ian DeLacy
Dr R.M Mswaka
Total pages 121
Language eng
Subjects L
300203 Plant Improvement (Selection, Breeding and Genetic Engineering)
300204 Plant Protection (Pests, Diseases and Weeds)
Formatted abstract
Genetic diversity studies using molecular markers reveal patterns of diversity in crops that are obscured by the complexities of pedigree records. The pattern of information revealed can be applied in different ways depending on the objectives of the study. In this study, diversity studies in tropical maize hybrids and inbred lines were carried out using SSR markers with the broad objectives of predicting heterosis for yield and gray leaf spot resistance, quantifying changes in allelic frequency in hybrids due to selection for gray leaf spot resistance and improve on the heterotic grouping of tropical maize inbred lines.

Three experiments were carried out. The first experiment involved analysis of genetic diversity of eight parental lines used in diallel trials for gray leaf spot resistance studies in Zimbabwe and Uganda. Genetic distances (Dij,) calculated on the basis of SSR variation of parental lines were then correlated with F1 hybrid performance for yield and GLS resistance, along with their general combining abilities (GCAs) and specific combining abilities (SCAs). Results showed a low but significant correlations between genetic distance and F1 hybrid yield and SCA for yield. The correlation coefficients of Dij with F1 hybrid performance for GLS resistance M'ere mostly not significant in the trials examined, indicating that Dij may not be useful for predicting heterosis for traits predominantly controlled by additive gene action as the case with GLS resistance. In addition no conclusive results from these experiments can be drawn on the prediction of heterosis and hybrid performance using molecular marker distance. Correlation coefficients based on specific inter-heterotic crosses were highly .significant for both F1 hybrid performances for yield and GLS resistance.

Loss of genetic diversity is always a concern in a breeding program. In the second experiment, the overall genetic diversity of 48 maize hybrids grown in Zimbabwe and their relationship for GLS resistance was studied. The calculated genetic distances among the hybrids ranged from 0.07-0.75 based on the Dice-Czekanowski similarity coefficient, indicating a moderately high genetic diversity among the hybrids. The relationship between GLS resistance and genetic diversity of the hybrids was done by correlating the genetic distances of the hybrids from the standard check. C3330. The results showed no significant correlation between the two, thus breeding for GLS resistant hybrids may only have resulted in qualitative rather than quantitative shift in genetic diversity. The analysis of molecular variance on hybrids from different seed companies grouped on the level of GLS resistance supported this conclusion indicating a highly substantial genetic diversity within hybrids within groups.

Heterotic groups are important component of hybrid maize breeding programs and they usually predetermines the base germplasm for generation of breeders. The level and distribution of SSR polymorphisms in 46 tropical maize inbred lines commonly used in Zimbabwe was studied. The result showed that amount of allelic diversity among the inbred lines is high with an average of 5.87 alleles per locus. Clustering of the inbred lines based on allelic distribution using the UPGMA algorithm produced four heterotic groups. Further analysis of the data using multi-dimensional scaling grouped the inbred lines into three heterotic groups. 
Keyword Hybrid corn -- Zimbabwe
Hybrid corn -- Disease and pest resistance -- Genetic aspects -- Zimbabwe

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Tue, 23 Aug 2011, 11:45:11 EST by Ning Jing on behalf of The University of Queensland Library