Browsing Masters Degrees (Genetics) by Author "Badenhorst, Petrus Cornelius"
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- ItemIdentification of molecular markers for Thinopyrum distichum chromosomes contributing to salt tolerance(Stellenbosch : Stellenbosch University, 2000-12) Badenhorst, Petrus Cornelius; Marais, G. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.ENGLISH ABSTRACT: The detrimental effect of soil salinity on crop production is a growmg problem worldwide (Tanji, 1990b). The degree to which plants can tolerate high concentrations of salt in their rooting medium is under genetic control with different genetic and physiological mechanisms contributing to salt tolerance at different developmental stages (Epstein & Rains, 1987). Only limited variation exists for salt tolerance in the cultivated cereals. This has prompted attempts to select tolerant progeny following hybridisation of cultivated species and wild, salt-tolerant species. Thinopyrum distichum, an indigenous wheatgrass that is naturally adapted to saline environments (McGuire & Dvorak, 1981), was crossed with triticale (x Triticosecale) in an attempt to transfer its salt tolerance and other hardiness characteristics (Marais & Marais, 1998). The aims of this study were to (i) identify Thinopyrum chromosomes carrying genes for salt tolerance and to identify molecular markers for these chromosomes, (ii) identify a number of diverse monosomic and disomie addition plants. Bulked segregant analysis (BSA), in combination with AFLP, RAPD and DAF marker analysis was implemented to screen for polymorphisms associated with salt tolerance. Five putative AFLP markers and two RAPD markers were detected using bulks composed of salt tolerant plants and bulks composed of salt sensitive plants. The distribution of the markers in these bulks suggests that more than one Thinopyrum chromosome carry genes for salt tolerance. Salt tolerant monosomic and disomie addition plants were characterised for AFLP, RAPD and DAF polymorphisms in an attempt to find markers associated with the chromosome(s) conditioning salt tolerance. One salt tolerant monosomic and one disomie addition plant was identified. One AFLP and two RAPD markers were identified for the Thinopyrum chromosome( s) present in the monosomic addition plant, while three AFLP and three RAPD markers were identified for the disomie addition plant. An attempt was also made to identify diverse chromosome addition plants having complete or near complete triticale genomes plus an additional random Thinopyrum chromosome. Plants with 2n = 43 /44 were identified and characterised for molecular markers (AFLP and RAPD). Cluster analysis was used to group the putative monosomic or disomie addition plants according to the specific Thinopyrum chromosomes they retained. Seventeen AFLP and RAPD markers could be used to group the 24 putative addition plants into six broadly similar groups with different additional Thinopyrum chromosomes. While the members of each group are likely to carry the same additional Thinopyrum chromosomes, this may not necessarily be the case as the interpretation of the marker results is complicated by heterogeneity among plants with regard to the triticale background chromosomes they possess. It is also likely that chromosome translocations occurred during backerossing which may further complicate data. Nonetheless, it is now possible to select disomie addition plants from each group that are likely to represent different Thinopyrum chromosomes. The data will also be useful in future attempts to find further addition plants carrying the remaining Thinopyrum chromosomes.