Identification of molecular markers for Thinopyrum distichum chromosomes contributing to salt tolerance

[摘要] 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 rootingmedium is under genetic control with different genetic and physiological mechanisms contributingto salt tolerance at different developmental stages (Epstein & Rains, 1987). Only limited variationexists for salt tolerance in the cultivated cereals. This has prompted attempts to select tolerantprogeny following hybridisation of cultivated species and wild, salt-tolerant species. Thinopyrumdistichum, an indigenous wheatgrass that is naturally adapted to saline environments(McGuire & Dvorak, 1981), was crossed with triticale (x Triticosecale) in an attempt to transfer itssalt tolerance and other hardiness characteristics (Marais & Marais, 1998). The aims of this studywere to (i) identify Thinopyrum chromosomes carrying genes for salt tolerance and to identifymolecular markers for these chromosomes, (ii) identify a number of diverse monosomic anddisomie addition plants.Bulked segregant analysis (BSA), in combination with AFLP, RAPD and DAF marker analysis wasimplemented to screen for polymorphisms associated with salt tolerance. Five putative AFLPmarkers and two RAPD markers were detected using bulks composed of salt tolerant plants andbulks composed of salt sensitive plants. The distribution of the markers in these bulks suggests thatmore than one Thinopyrum chromosome carry genes for salt tolerance.Salt tolerant monosomic and disomie addition plants were characterised for AFLP, RAPD and DAFpolymorphisms in an attempt to find markers associated with the chromosome(s) conditioning salttolerance. One salt tolerant monosomic and one disomie addition plant was identified. One AFLPand two RAPD markers were identified for the Thinopyrum chromosome( s) present in themonosomic addition plant, while three AFLP and three RAPD markers were identified for thedisomie addition plant.An attempt was also made to identify diverse chromosome addition plants having complete or nearcomplete triticale genomes plus an additional random Thinopyrum chromosome. Plants with2n = 43 /44 were identified and characterised for molecular markers (AFLP and RAPD). Clusteranalysis was used to group the putative monosomic or disomie addition plants according to thespecific Thinopyrum chromosomes they retained. Seventeen AFLP and RAPD markers could beused to group the 24 putative addition plants into six broadly similar groups with differentadditional 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 theinterpretation of the marker results is complicated by heterogeneity among plants with regard to thetriticale background chromosomes they possess. It is also likely that chromosome translocationsoccurred during backerossing which may further complicate data. Nonetheless, it is now possible toselect disomie addition plants from each group that are likely to represent different Thinopyrumchromosomes. The data will also be useful in future attempts to find further addition plantscarrying the remaining Thinopyrum chromosomes.

[发布机构] Stellenbosch University