Two manuscripts with conflicting results on the mapping location of stem rust resistance gene Sr13 in wheat are published in this issue of TAG (Admassu et al. and Simons et al.). Both resistance genes were mapped on the long arm of chromosome 6AL, but the gene mapped by Admassu et al. between markers barc37 and wmc256 is more than 50 cM proximal to the one mapped by Simons et al. between markers CD926040 and BE471213.
After the publication of the two manuscripts in TAG online, the authors of both manuscripts became aware of the conflicting results and they exchanged the critical hexaploid wheat cytogenetic stocks Khapstein/9*LMPG (developed by Dr. D. Knott) and the recurrent parent LMPG to determine the source of the differences. In addition, they requested seeds for these two stocks from the U.S. Cereal Disease Laboratory in Saint Paul Minnesota (Dr. Yue Jin) and from Canada Agri-Food, Winnipeg (Dr. Tom Fetch).
Analysis of these stocks with molecular markers for the long arm of chromosome 6AL revealed that the Khapstein/9*LMPG seed stock used in the Admassu et al. paper was different from the other three Khapstein/9*LMPG stocks. Molecular markers barc37, barc107, barc118, barc1165, gwm570, wmc179, wmc256, wmc580, and cfd2 all showed different bands in the seed stock used in the Admassu paper relative to the seed stocks from the University of California, the Cereal Disease Laboratory and Agri-Food Canada.
These results indicate that the Khapstein/9*LMPG seed stock used in the Admassu paper is different from the other three. Since the Khapstein/9*LMPG hexaploid genetic stock defines the gene name Sr13, the gene mapped by Admassu et al. is most likely not Sr13 and should be renamed.
The Khapstein/9*LMPG developed by Dr. D. Knott is polymorphic with the LMPG recurrent parent only for markers closely linked to the stem rust resistance gene mapped in the four tetraploid populations in the distal region of chromosome arm 6AL (barc104b and dupw167) by Simons et al. This observation, together with the fact that Sr13 was originated in tetraploid wheat (Khapli), provides indirect evidence that the gene mapped by Simons et al. is Sr13. Mapping the stem rust resistance gene present in the correct Khapstein/9*LMPG stock in an hexaploid segregating population will provide the final answer.
Interestingly, both genes confer resistance to the new stem rust race Ug99 (TTKSK) suggesting that it would be possible to combine the two sources of resistance to Ug99 in the same 6AL arm. We have initiated crosses between the correct Khapstein/9*LMPG genetic stock and the source of the Admassu et al. Ug99 resistance to recombine both genes.
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Dubcovsky, J., Ordon, F., Perovic, D. et al. Conflicting mapping results for stem rust resistance gene Sr13 . Theor Appl Genet 122, 659 (2011). https://doi.org/10.1007/s00122-010-1495-2