Abstract
Septoria tritici blotch (STB) is one of the most devastating foliar diseases of wheat worldwide. Host resistance is the most economical and safest method of controlling the disease, and information on resistance loci is crucial for effective breeding for resistance programs. In this study we used a mapping population consisting of 126 doubled-haploid lines developed from a cross between the resistant cultivar Mandub and the susceptible cultivar Begra. Three monopycnidiospore isolates of Z. tritici with diverse pathogenicity were used to test the mapping population and parents’ STB resistance at the seedling stage (under a controlled environment) and adult plant stage (polytunnel). For both types of environments, the percentage leaf area covered by necrosis (NEC) and pycnidia (PYC) was determined. A linkage map comprising 5899 DArTSNP and silicoDArT markers was used for the quantitative trait loci (QTL) analysis. The analysis showed five resistance loci on chromosomes 1B, 2B and 5B, four of which were derived from cv. Mandub. The location of QTL detected in our study on chromosomes 1B and 5B may suggest a possible identity or close linkage with Stb2/Stb11/StbWW and Stb1 loci, respectively. QStb.ihar-2B.4 and QStb.ihar-2B.5 detected on chromosome 2B do not co-localize with any known Stb genes. QStb.ihar-2B.4 seems to be a new resistance locus with a moderate effect (explaining 29.3% of NEC and 31.4% of PYC), conferring resistance at the seedling stage. The phenotypic variance explained by QTL detected in cv. Mandub ranged from 11.9% to 70.0%, thus proving that it is a good STB resistance source and can potentially be utilized in breeding programs.
Highlights
Septoria tritici blotch (STB), a fungal disease caused by the ascomycete fungus Zymoseptoria tritici (Desm.)
The most noteworthy examples of this phenomenon were observed for the susceptible parental line Begra: T_IPO92006_PYC (24.63% of the leaf area covered by necrotic lesions bearing pycnidia when the population maximum was 74.59%), T_IPO88004_PYC (21.02%, max. 67.10%) and F_IPO88004_PYC (16.21%, max. 70.99%)
The assumptions of co-localization need to be taken with caution. Supposed positions of both quantitative trait loci (QTL) detected in this study as well as known resistance loci are marked on generated physical maps, which can be found in Supplementary Figures S1, S2 and S3
Summary
Septoria tritici blotch (STB), a fungal disease caused by the ascomycete fungus Zymoseptoria tritici (Desm.) Septoria tritici), is one of the most devastating foliar diseases of wheat, which accounts for approximately 70% of the annual usage of cereal fungicide in Europe [1,2]. Wind-dispersible ascospores on wheat debris are the most significant source of primary inoculum and contribute greatly to year-to-year disease transmission, but the asexual pycnidiospores promote polycyclic host infection and spread of the disease over a growing season [3]. Severe yield losses can occur in crops when the top leaves become infected, as flag leaf photosynthesis in wheat contributes about 30%–50% of the assimilates for grain filling [5,6]. As the risk of an epidemic can be reduced by good agricultural practices, seeking new sources of resistance to STB should be a priority, especially given the reports concerning the possible rapid development of fungicide resistance in Z. tritici populations
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