Identifier

etd-01202005-134859

Degree

Master of Science (MS)

Department

Plant, Environmental Management and Soil Sciences

Document Type

Thesis

Abstract

Genetic diversity is indispensable to sustain genetic gain in breeding programs. Cultivated sugarcane is a highly heterozygous hybrid derived from crossing two highly heterozygous parents. Sugarcane breeders traditionally rely on pedigree records to select parents. Molecular markers now make it possible to assess genetic diversity at the DNA level. Sixty three sugarcane clones were characterised using Target Region Amplification Polymorphism (TRAP) markers and pedigree relationship (Coefficient of parentage (COP)). The TRAP is a PCR-based marker with a fixed primer designed from Expressed Sequence Tag (EST) sequences paired with an arbitrary primer. It is supposed to unravel trait based polymorphism in the intronic- or exonic-regions of the genome. Ten genes evidently involved in sucrose accumulation (SUC), cold tolerance (CT) and trichome development (TRICH) were paired with four arbitrary primers. A total of 3,170 bands were scored of which 2,684 (85%) were polymorphic. Cluster and Multi Dimensional Scaling (MDS) analyses revealed a very narrow genetic diversity among the entries with genetic similarity (GS) ranging from 78 to 94%. Parentage did not seem to contribute to the grouping pattern in either the overall or individual gene family (SUC, CT and TRICH) clusters which was confirmed by the lack of correlation (r = -0.008) between the TRAP and COP-derived GS matrices. The complex genome of sugarcane and the strict assumptions inherent with estimating COP may account for this disparity. Analysis of Molecular Variance (AMOVA) revealed no structure in the population with regards to era of release (Pre- versus post-1980) with among clones accounting for up to 99% of the total variation and only 1% of variation attributable to era of release. Mixed Model Analysis on the MDS axes generally revealed no significant differences among era of release. Thus, pedigree records can enhance interpretation of marker-derived information especially in an interspecific crop like sugarcane where ancestral species possess and contribute different characteristics. Results from this study needs to be supplemented with sequence analysis of TRAP fragments to definitively relate the derived information to trait variation.

Date

2005

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Collins Kimbeng

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