Epsilon Archive for Student Projects

Abstract

Wheat-rye translocations involving 1RS and 2RL of rye are the most useful sources of genes for disease resistance in wheat breeding. Rye genes are known to control resistance to biotic and abiotic stresses. Wheat-rye translocations have been widely used by breeders all over the world because genes located on translocated chromosome arms or fragments from the rye genome can determine a number of useful traits in wheat, such as high yield, wide adaptation, diseases and pest resistance.
The wheat-rye translocation lines used in this study were derived from a cross between the Swedish bread wheat variety Topper and the line KR99-139 being homozygous for the two different wheat-rye translocations 1BL/1RS and 2RL/2BS. BC1F1 materials were obtained through one back-cross with either the line KR99-139 or the variety Topper. Thereafter, BC1F2 and BC1F3 were obtained by once and twice selfing. In the obtained material, it was thereafter possible to define four different possible homozygous translocation combinations. Thus, lines containing both 1RS and 2RL translocations, containing only 1RS or 2RL and without any translocation were identified.
For identification of the four possible homozygous wheat-rye translocation lines mentioned above, three different methods were used. First, lines of different types were characterized and isolated based on a phenotypical marker, i.e. if the plant showed red or green coleoptile colour. Plants with homozygous presence of 2RL were known to develop red coleoptile, as a gene for red coleoptile has been verified to be present at 2RL in these lines. The analyses of coleoptile colours were done in the BC1F2 (obtained from selfed BC1F1 lines determined by molecular markers at BAZ, Germany to be 1RS– –/2RL+–) and BC1F3 (obtained from the BC1F2 lines having a red coleoptile) wheat-rye translocation lines, where the variety Topper had been used for backcrossing. Moreover, the BC1F2 (obtained from selfed BC1F1 lines determined by molecular markers at BAZ, Germany to be 1RS++/2RL+–) wheat-rye translocation lines for which the KR99-139 line was used for backcrossing, was selfed, and analyses of coleoptile colours were done in the BC1F3 (on a representative sample of all combinations of presence and absence of 2RL). The results from the coleoptiles colour analyses generally showed that it was possible to distinguish lines having 2RL++ (red coleoptiles) and 2RL– – (green coleoptiles).
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Plants having 2RL+– were sometimes classified as having green and sometimes as having red coleoptiles. Therefore, if coleoptiles colour is going to be used for selection of lines with presence/absence of 2RL in homozygous form, at least two generations have to be analyzed and lines not segregating in either of the analyses can be judged as being homozygous as related to their coleoptiles colour. For identification of lines with presence of heterozygous 1RS+– and homozygous 2RL++ rye chromosome the Giemsa C-banding technique was used. The Giemsa C-banding techniques on the BC1F3 segregating population generally resulted in well-defined sharp, distinct bands in the wheat-rye translocation lines and both the rye chromosome arms, 1RS and 2RL were identified. Additionally, five microsatellite (SSR) markers SCM9, SCM39, SCM43, SCM69 and SCM75 were used for verification of the presence of 1RS and 2RL. Among the five SSR markers, SCM9 and SCM75 resulted in reliable amplification of expected products, 220 bp and 191 bp respectively. The line KR99-139 containing both 1RS and 2RL showed correct amplification products with both mentioned primers while the bread wheat variety Topper without any rye chromosome showed no amplification with both SSR primers pairs.
Resistance towards yellow rust and stem rust were evaluated through seedling resistance test in the greenhouse (Global Rust Reference Center, Denmark) to Puccinia striiformis, and adult plant resistance to Puccinia graminis, race Ug99 (TTKSK) in Njoro, Kenya. For the seedling resistance test, pathogenicity of 17 races/isolates of yellow rust was used. The BC1F3 which carries combination of 1RS++/2RL++, 1RS++/2RL+– and the KR99-139 were found to be highly resistant to some races/isolates whether the variety Topper was fully susceptible to all races/isolates. The results showed Yr9 to be one possible gene that could be responsible for the obtained yellow rust resistance. However, the results were not that clear so than not other possible genes could also be an alternative. For adult plant resistance towards Ug99, a total of 28 of the BC1F3 wheat-rye translocation lines and their parents were evaluated in the field of Njoro, Kenya. The results indicated that out of the 30 tested lines 20 were susceptible, 8 moderately susceptible to susceptible and in 2 lines the resistance to Ug99 was identified. The two BC1F3 wheat-rye translocation lines that were found to be resistant towards Ug99 were both being homozygous for 1RS++ and heterozygous for 2RL+–. Thus, these results indicated presence of several genes/QTLs controlling resistance indicating possible epistatic effects of the genes involved. The lines identified as resistant will be utilized in combination with Tajik germplasm
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to develop a mapping population for determining the underlying basis of resistance. To summarize results from the research outlined in this thesis indicate that wheat-rye translocation lines and used methods can be highly relevant for wheat breeding programs and further research.