Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/9/2007
Publication Date: 7/30/2007
Citation: Klindworth, D.L., Miller, J., Jin, Y., Xu, S.S. 2007. Chromosomal locations of genes for stem rust resistance in monogenic lines derived from tetraploid wheat accession ST464. Crop Science. 47:1441-1450. Interpretive Summary: Stem rust is one of the most devastating diseases of wheat, including durum wheat which is used in pasta products. An accession of durum wheat from Ethiopia called ST464 is known to have at least four genes for resistance to stem rust. By crossing to a stem rust susceptible durum wheat, each of the four known genes in ST464 had been previously transferred to a line carrying only one resistance gene. These four lines, identified as ST464-A1, ST464-A2, ST464-B1, and ST464-C1, were crossed to stem rust susceptible stocks that are used for locating genes to specific chromosomes. We observed chromosome pairing in the hybrids of these crosses. We observed that a translocation, indicating an interchange of chromosomal segments, had occurred between the chromosomes identified as 2A and 4B. The hybrids were crossed to a stem rust susceptible durum called Rusty. Chromosome pairing and tests for stem rust susceptibility were then conducted. From those tests, we determined that the genes in the lines ST464-A1, ST464-A2, ST464-B1, and ST464-C1 were located to chromosomes 6A, 2B, 4A, and 6A, respectively. We then compared the reactions of the four lines to several stem rust pathotypes and compared those reactions to those of known genes. The reactions of ST464-A2 and ST464-C1 to those pathotypes indicated that the genes in those lines were identical to stem rust resistance genes Sr9e, and Sr13, respectively.
Technical Abstract: The genetics of resistance to stem rust (Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & Henn.) in durum (Triticum turgidum L. ssp. durum) is not as well understood as for hexaploid wheat (T. aestivum L.). Our objective was to determine the chromosomal location of genes for stem rust resistance in four monogenic lines derived from the Ethiopian tetraploid landrace ST464. The four monogenic lines were crossed to a set of stem rust susceptible aneuploids based on the tetraploid line 47-1. We observed chromosome pairing in the hybrids and made testcrosses to Rusty durum. Monogenic lines ST464-A1 and ST464-A2 were observed to carry a 2A/4B translocation, and subsequent crosses proved that the translocation was derived from ST464. Testcross F2 seedlings were inoculated with one of three stem rust pathotypes and classified for segregation for resistance to identify the critical chromosome for each monogenic line. The stem rust resistance genes in monogenic lines ST464-A1, ST464-A2, ST464-B1, and ST464-C1 were located to chromosomes 6A, 2B, 4A, and 6A, respectively. The four ST464 monogenic lines and hexaploid lines carrying Sr9e and Sr13 were then tested with eight stem rust pathotypes with the objective of postulating the genes present in the monogenic lines. The genes in ST464-A2 and ST464-C1 were postulated to be Sr9e, and Sr13, respectively.