Location: Cereal Crops ResearchTitle: Molecular and cytogenetic characterization of wheat introgression lines carrying the stem rust resistance gene Sr39.) Author
Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/6/2010
Publication Date: 5/21/2010
Citation: Yu, G., Zhang, Q., Klindworth, D.L., Friesen, T.L., Knox, R., Jin, Y., Zhong, S., Cai, X., Xu, S.S. 2010. Molecular and Cytogenetic Characterization of Aegilops Speltoides Chromosome Segments Carrying Sr39 in the Original Translocation Stock and Derived Wheat Lines. Crop Science. 50:1393–1400. Interpretive Summary: The new stem rust races known as Ug99 are devastating to wheat. One gene that can control Ug99 is Sr39. This gene was found in a wild wheat and as a consequence, whenever breeders attempt to use Sr39 in crosses, many undesirable genes that are linked to Sr39 are also transferred to wheat. Our objective for this study was to find molecular markers that are linked to Sr39. These markers can be used to determine if the chromosome from wild wheat has been shortened, thereby eliminating some of the undesirable linked genes. After finding molecular markers that are evenly spaced across the entire length of the wild wheat chromosome, we analyzed fourteen different translocation lines. Lines RL5711 and RL6082 were determined to still retain the entire long arm and 85 percent of short arm of wild wheat chromosome 2. Line PI 600683 was found to have 93 percent of long arm and 85 percent of short arm of the wild wheat chromosome. Of the remaining lines analyzed, only P9714-AM03C51 was found to have a shorter wild wheat chromosome segment than found in PI 600683; and, this line had 93 percent of long arm and 60% of short arm of the wild wheat chromosome. These results were confirmed by microscopic examination of the chromosomes (fluorescent staining). P9714-AM03C51 may therefore be useful for breeders; but, one drawback of eliminating the undesirable linked genes is that the desired gene (Sr39) may be accidentally lost. To test this, we inoculated P9714-AM03C51 and its parents with 9 races of stem rust. Because the parents were as rust resistant as P9714-AM03C51, we were not able to determine if P9714-AM03C51 still retained Sr39. The molecular markers that we found will be useful in additional attempts to reduce the size of the wild wheat segment.
Technical Abstract: Stem rust, caused by Puccinia graminis Pers.:Pers. f.sp. tritici Eriks. and Henn., poses a serious threat to global wheat production because of the emergence of Pgt-TTKSK (Ug99). The TTKSK resistant gene Sr39 was derived from Aegilops speltoides through chromosome translocation. In this study, we characterized Sr39 translocation lines in four different wheat backgrounds with fluorescent genomic in situ hybridization (GISH) and simple sequence repeat (SSR) markers. The results indicated that the translocation lines, RL5711 and RL6802, contain the same size of translocated Ae. speltoides chromosome segment which includes long arm (L) and approximately 85% of short arm (S) of chromosome 2S. PI 600683 has lost the telomere end of the 2SL and contains approximately 85% of 2SS and 93% of 2SL. Five translocation lines derived from the cross PI 600683/2*HY438 contain the same size of the translocated speltoides chromosome segment as found in PI 600683. However, the line P9714-AM03C51, derived from PI 600683/2*HY438, contains a shortened Ae. speltoides chromosome segment which includes approximately 93% of 2SL and 60% of 2SS. The study demonstrated that it is feasible to shorten the Ae. speltoides chromosome segment in wheat- Ae. speltoides translocation line. The GISH results and SSR markers identified here will be useful for chromosome manipulation to further shorten the Ae. speltoides.