Ontwikkeling van molekulere merkers vir wilde-spesie-verhaalde weerstandsgeenkomplekse van gewone koring

Eksteen, Aletta (2009-03)

Thesis (MSc (Genetics))--University of Stellenbosch, 2009.

Thesis

Worldwide, the rust diseases cause significant annual wheat yield losses (Wallwork 1992; Chrispeels & Sadava 1994). The utilization of host plant resistance to reduce such losses is of great importance particularly because biological control avoids the negative environmental impact of agricultural chemicals (Dedryver et al. 1996). The wild relatives of wheat are a ready source of genes for resistance to disease and insect pests. A large degree of gene synteny still exists among wheat and its wild relatives (Newbury & Paterson 2003). It is therefore possible to transfer a chromosome segment containing useful genes to a homologous region in the recipient genome without serious disruption of genetic information. Special cytogenetic techniques are employed to transfer genes from the wild relatives to the wheat genomes (Knott 1989). Unfortunately the transfer of useful genes may be accompanied by the simultaneous transfer of undesirable genes or redundant species chromatin which has to be mapped and removed (Feuillet et al. 2007). DNA markers are extremely useful for the characterisation and shortening of introgressed regions containing genes of interest (Ranade et al. 2001), and may also be used for marker aided selection of the resistance when the genes are employed commercially. Eight wheat lines containing translocations/introgressions of wild species-derived resistance genes were developed by the Department of Genetics (SU). These lines are presently being characterized and mapped and attempts are also being made to shorten the respective translocations. This study aimed to find DNA markers for the various translocations and to convert these into more reliable SCAR markers that can be used in continued attempts to characterize and improve the respective resistance sources. A total of 260 RAPD and 21 RGAP primers were used to screen the eight translocations and, with the exception of Lr19, it was possible to identify polymorpic bands associated with each translocation. However, it was not possible to convert all of these into more reliable SCAR markers. The primary reason for this was the low repeatability of most of the bands. Certain marker fragments turned out to be repeatable but could not be converted successfully. Some of the latter can, however, be used directly (in RAPD or RGAP reactions) as markers. The Lr19 translocation used in the study (Lr19-149-299) is a significantly reduced version of the original translocation and failure to identify polymorphisms associated with it can probably be ascribed to its small size. The following numbers of markers (direct and converted into SCARs) were Worldwide, the rust diseases cause significant annual wheat yield losses (Wallwork 1992; Chrispeels & Sadava 1994). The utilization of host plant resistance to reduce such losses is of great importance particularly because biological control avoids the negative environmental impact of agricultural chemicals (Dedryver et al. 1996). The wild relatives of wheat are a ready source of genes for resistance to disease and insect pests. A large degree of gene synteny still exists among wheat and its wild relatives (Newbury & Paterson 2003). It is therefore possible to transfer a chromosome segment containing useful genes to a homologous region in the recipient genome without serious disruption of genetic information. Special cytogenetic techniques are employed to transfer genes from the wild relatives to the wheat genomes (Knott 1989). Unfortunately the transfer of useful genes may be accompanied by the simultaneous transfer of undesirable genes or redundant species chromatin which has to be mapped and removed (Feuillet et al. 2007). DNA markers are extremely useful for the characterisation and shortening of introgressed regions containing genes of interest (Ranade et al. 2001), and may also be used for marker aided selection of the resistance when the genes are employed commercially. Eight wheat lines containing translocations/introgressions of wild species-derived resistance genes were developed by the Department of Genetics (SU). These lines are presently being characterized and mapped and attempts are also being made to shorten the respective translocations. This study aimed to find DNA markers for the various translocations and to convert these into more reliable SCAR markers that can be used in continued attempts to characterize and improve the respective resistance sources. A total of 260 RAPD and 21 RGAP primers were used to screen the eight translocations and, with the exception of Lr19, it was possible to identify polymorpic bands associated with each translocation. However, it was not possible to convert all of these into more reliable SCAR markers. The primary reason for this was the low repeatability of most of the bands. Certain marker fragments turned out to be repeatable but could not be converted successfully. Some of the latter can, however, be used directly (in RAPD or RGAP reactions) as markers. The Lr19 translocation used in the study (Lr19-149-299) is a significantly reduced version of the original translocation and failure to identify polymorphisms associated with it can probably be ascribed to its small size. The following numbers of markers (direct and converted into SCARs) were v identified: S8-introgression (Triticum dicoccoides) = one RAPD and two SCARs; S13-translocation (Aegilops speltoides) = four RAPDs, three RGAPs and five SCARs; S15-translocation (Ae. peregrina) = one RAPD and two SCARs; S20-translocation (Ae. neglecta) = two RAPDs, two RGAPs and one SCAR. The markers are already being employed in current projects aiming to map and shorten these translocations. Some of the markers can be combined in multiplex reactions for more effective mass screening. No repeatable markers could be identified for the four remaining translocations (S12 from Ae. sharonensis; S14 from Ae. kotschyi; Smac from Ae. biuncialis and Lr19-149-299 from Thinopyrum ponticum).

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