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Septoria tritici blotch (STB), caused by Mycosphaerella graminicola(synonym: Zymoseptoria tritici; asexual stage: Septoria tritici), is an important disease of wheat (Triticum aestivumL.) worldwide. Management of the disease usually is by host resistance or fungicides. However, M. graminicolahas developed insensitivity to most commonly applied fungicides, so there is a continuing need for well‐characterized sources of host resistance to accelerate the development of improved wheat cultivars. Gene Stb3has been a useful source of major resistance, but its mapping location has not been well characterized. On the basis of linkage to a single marker, a previous study assigned Stb3to a location on the short arm of chromosome 6D. However, the results from the present study show that this reported location is incorrect. Instead, linkage analysis revealed that Stb3is located on the short arm of wheat chromosome 7A, completely linked to microsatellite (simple‐sequence repeat) locus Xwmc83and flanked by loci Xcfa2028(12.4 cM distal) and Xbarc222(2.1 cM proximal). Linkage between Stb3and Xwmc83was validated in BC1F3progeny of other crosses, and analyses of the flanking markers with deletion stocks showed that the gene is located on 7AS between fraction lengths 0.73 and 0.83. This revised location of Stb3is different from those for other STB resistance genes previously mapped in hexaploid wheat but is approximately 20 cM proximal to an STB resistance gene mapped on the short arm of chromosome 7Amin Triticum monococcum. The markers described in this study are useful for accelerating the deployment of Stb3in wheat breeding programs.

The development of adapted wheat germplasm is essential so that breeding programs can develop superior cultivars, which was the objective of this research. ND 803 is hard red spring wheat (HRSW; Triticum aestivumL.) line that was developed at North Dakota State University (NDSU) and released by the North Dakota Agricultural Experiment Station (NDAES). ND 803 (Reg. No. GP‐947, PI 665931 was derived from the ND2831/FO.2808 cross made at NDSU in fall 1997. ND2831 (‘Sumai3’ [PI 481542]/‘Stoa’ [PI 520297]) is a hard red spring experimental line with good resistance to Fusarium head blight (FHB), or scab [caused by Fusarium graminearumSchwabe; telomorph Gibberella zeae(Schwein.) Petch] originating from ‘Sumai3’, which is known to possess the Fhb1quantitative trait locus. Sumai3 is a spring wheat from China that is arguably the most widely used source of resistance to FHB in the world. Stoa is an HRSW cultivar released by NDSU in 1984. FO.2808 (‘Grandin’ [PI 531005]/3/IAS20*4/H567.71//‘Amidon’ [PI 527682]/ND674) is an HRSW line developed by the NDSU HRSW breeding program. Amidon and Grandin are HRSW cultivars released by NDAES in 1988 and 1989, respectively. IAS20*4/H567.71 is a public breeding line received from CIMMYT. ND 803 was produced from a bulk of one purified F5:6plot selected in 2000 at Prosper, ND. ND 803 was released because it combines good agronomic and end‐use quality with resistance to both FHB and leaf diseases.

Providing wheat (Triticum aestivumL.) growers and industry with adapted wheat cultivars with high‐quality attributes is essential for maintaining wheat as a competitive crop in the spring‐wheat growing region of the USA. Therefore, our breeding program aims to develop modern wheat cultivars using both traditional and modern breeding tools. ‘Prosper’ (Reg. No. CV‐1080, PI 662387) hard red spring wheat was developed at North Dakota State University and released jointly by the North Dakota Agricultural Experiment Station and the Minnesota Agricultural Experiment Station because of its good adaptation to the spring‐wheat‐growing regions in the U.S. North Central Plains. However, the high yield potential of Prosper under high rainfall conditions makes it more adapted mainly to wheat‐growing regions in eastern North Dakota, western Minnesota, and high‐rainfall regions of neighboring states. It has high yield potential and good milling and baking properties. Gene postulation shows that Prosper has the Lr21gene, which confers resistance to leaf rust (caused by Puccinia triticinaEriks.). However, 2011 field observations show that Prosper is susceptible to a new race that overcomes the Lr21gene. Prosper is resistant to stem rust (caused by Puccinia graminisPer.:Pers. f. sp. triticiEriks. & E. Henn) and moderately resistant to Fusarium head blight (FHB), or scab [caused by Fusarium graminearumSchwabe; telomorph Gibberella zeae(Schwein.) Petch].

Septoria tritici blotch (STB) of wheat (Triticum aestivumL.), caused by the fungal pathogen Mycosphaerella graminicola(Fuckel) J. Schröt. in Cohn (anamorph: Septoria triticiRoberge in Desmaz.), occurs naturally in all wheat production areas around the world. Two genes for resistance to this disease, Stb2and Stb3, have been identified in wheat germplasm and together confer resistance to the most prevalent strains of M. graminicolain Australia and the USA. However, so far neither gene has been mapped in the wheat genome and their linkage relationships to other markers are not known. The objectives of this study were to identify molecular markers linked to the STB resistance genes Stb2and Stb3and to map these genes in the wheat genome. Genetic families of doubled‐haploid populations segregating for Stb2and Stb3were evaluated in the greenhouse for STB reaction during the spring and fall seasons of 2002 and 2003. Genomic DNA isolated from each segregating population was analyzed with microsatellite or simple‐sequence repeat (SSR) markers in bulked‐segregant analysis to identify those that cosegregated with the STB phenotypes. Linkage analysis identified five SSR markers near the Stb2gene on the distal region of the short arm of chromosome 3B. Loci Xgwm389and Xgwm533.1were approximately 1 cM distal to Stb2, which itself was 3.7 cM distal to Xgwm493In addition to Stb2, this genomic region contains multiple genes conferring resistance to taxonomically diverse fungal pathogens of wheat, including a major quantitative trait locus for resistance to Fusarium head blight (caused by Fusarium graminearumSchwabe). The SSR marker Xgdm132was linked to the Stb3gene at a distance of approximately 3 cM on the short arm of chromosome 6D. The microsatellite markers identified in this study should facilitate marker‐assisted selection and pyramiding of Stb2and Stb3with other STB resistance genes for more durably resistant wheat.