Mapping of new quantitative trait loci (QTL) for resistance to Septoria tritici blotch in spring wheat (Triticum aestivum L.)

Septoria tritici blotch (STB), caused by Zymoseptoria tritici (synonyms: Mycosphaerella graminicola and Septoria tritici), is a devastating disease of wheat (Triticum aestivum L.) worldwide. STB can be managed by fungicide application and by host resistance. The use of fungicides is less effective due to the development of fungal populations resistant to commercially available fungicides. As a result, host plant resistance is considered as one of the best strategies of STB management. In our preliminary study, the spring wheat cultivar 'Largo' showed a high level of resistant to multiple isolates of Z. tritici. The main objective of this study was to identify quantitative trait loci (QTL) for STB resistance in Largo and DNA markers associated with QTL. The 118 F-7 recombinant-inbred lines were developed from a cross between the synthetic hexaploid wheat Largo and the spring wheat susceptible line ND495 by single-seed descent. Disease severity in the mapping population was assessed at flag leaf stage 21 days after inoculation in the greenhouse at North Dakota State University, Fargo, ND in 2009 and 2010. Approximately, 2500 Diversity Arrays Technology(A (R)) (DArT) markers were used for genetic mapping. Among them, 263 DArT markers were polymorphic and revealed the 37 linkage groups. The new putative QTL (QStb.2A) associated with STB resistance was flanked by the two DArT markers wPt_3896 and wPt_4197, (wPt_4555) and is mapped on chromosome 2A. Single marker analysis also detected three additional DArT markers associated with other QTLs; however, chromosomal locations of these markers are unknown. Our results indicated that the DArT markers identified in this study can be useful for marker-assisted selection in wheat breeding programs and for combing this novel QTL with other STB resistance genes.