Department of Genetics

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Browsing Department of Genetics by Author "Badenhorst, Pieter Engelbertus"

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    Poging om die Aegilops sharonensis-verhaalde Lr56/Yr38 koringtranslokasie te verkort
    (Stellenbosch : Stellenbosch University, 2008-12) Badenhorst, Pieter Engelbertus; Marais, G. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.
    ENGLISH ABSTRACT: The wheat resistance genes, Lr56 (leaf rust) and Yr38 (stripe rust), occur on an Aegilops sharonensis-derived translocation which spans the entire 6AS chromosome arm as well as a large proximal region of 6AL. This study aimed to identify recombinant forms of this translocation in which excess foreign chromatin was replaced with common wheat chromatin without loss of the resistance genes. In January of 2007 the plant breeding program of the University of Stellenbosch conducted a homoeologous-pairing induction experiment with the translocation. The purpose of the experiment was to promote homoeologous meiotic recombination (through absence of the Ph1-locus) between Triticum aestivum chromosome A6 and the Lr56/Yr38-translocation. A large number of F1 test-cross progeny was produced. In this study the material was characterized with molecular markers in order to identify useful, shortened forms of the translocation. Maps of chromosome 6A of Triticum aestivum (Röder et al. 1998 Sourdille et al. 2004) were consulted to identify potentially useful microsatellite markers for mapping the translocation. Six microsatellite markers that span the translocated segment were then used in an initial characterization of the testcross-population, 06M04. This identified a subset of plants that were recombinants. Genetic analysis of the data showed that the resistance genes were probably located on the 6AL arm close to the translocation breakpoint. The data also made it possible to identify an even smaller panel of recombinants that were likely to include the shortest forms. Three additional microsatellite loci that were likely to occur in the general region of the resistance genes were identified and tested on the smaller panel. In the absence of further useful, mapped microsatellite markers it was necessary to find additional markers in an attempt to further map the resistance and identify still shorter recombinants. The smaller panel of recombinants was therefore tested for polymorphic AFLP loci making use of 33 MseI/EcoRI-primer combinations as well as an MseI/PstI-primer combination. The AFLP-analysis produced six polymorphic loci which could be used to identify further shortened translocations. Three of the original 156 leaf rust resistant plants that retained the smallest amounts of foreign chromatin were identified. The translocations in these plants are probably similar in size and it may be difficult to determine which is the shortest. Since the study focused on mapping Lr56 it will be necessary to also characterize the material for stripe rust resistance in order to locate Yr38. The large reduction in the size of the translocation will facilitate commercial utility of Lr56 (and Yr38?). However, it will be necessary to do a thorough agronomic evaluation of the reduced translocations to ascertain that no deleterious special chromatin remained.