Abstract
Bacterial leaf streak (BLS) caused by Xanthomonas campestris pv. translucens is one of the major bacterial diseases threatening wheat production in the United States Northern Great Plains (NGP) region. It is a sporadic but widespread wheat disease that can cause significant loss in grain yield and quality. Identification and characterization of genomic regions in wheat that confer resistance to BLS will help track resistance genes/QTLs in future wheat breeding. In this study, we evaluated a hard winter wheat association mapping panel (HWWAMP) containing 299 hard winter wheat lines from the US hard winter wheat growing region for their reactions to BLS. We observed a range of BLS responses among the lines, importantly, we identified ten genotypes that showed a resistant reaction both in greenhouse and field evaluation. Genome-wide association analysis with 15,990 SNPs was conducted using an exponentially compressed mixed linear model. Five genomic regions (p < 0.001) that regulate the resistance to BLS were identified on chromosomes 1AL, 1BS, 3AL, 4AL, and 7AS. The QTLs Q.bls.sdsu-1AL, Q.bls.sdsu-1BS, Q.bls.sdsu-3AL, Q.bls.sdsu-4AL, and Q.bls.sdsu-7AS explain a total of 42% of the variation. In silico analysis of sequences in the candidate regions on chromosomes 1AL, 1BS, 3AL, 4AL, and 7AS identified 10, 25, 22, eight, and nine genes, respectively with known plant defense-related functions. Comparative analysis with rice showed two syntenic regions in rice that harbor genes for bacterial leaf streak resistance. The ten BLS resistant genotypes and SNP markers linked to the QTLs identified in our study could facilitate breeding for BLS resistance in winter wheat.
Highlights
Wheat (Triticum aestivum L.) is one of the major cereal crops worldwide
A total of four significant regions were obtained with one each on chromosome 1A, 1B, 4A, and 7A (Fig. 2A, Table S4) that showed an association with Bacterial leaf streak (BLS) resistance, whereas from the field evaluation, we only identified three significant genomic regions on the chromosomes 1A, 4A, and 7A (Fig. 2B, Table S4) in hard winter wheat association mapping panel (HWWAMP)
When best linear unbiased estimator (BLUE) values were used for GWAS analysis, we identified a total of five genomic regions associated with BLS resistance located on chromosomes 1A, 1B, 3A, 4A, and 7A (Fig. 2C, Table S4)
Summary
Wheat (Triticum aestivum L.) is one of the major cereal crops worldwide. Hard winter wheat contributes 40% (United States Department of Agriculture, 2016) of the total wheat production in the USA; it has been challenged by several biotic and abiotic factors, which could limit yield potential and seed quality (Pandey et al, 2017). BLS can lead to yield losses of up to 40% (Tillman et al, 1999; Mehta, 2014) and can affect protein content, degrading the grain quality (Duveiller, Van Ginkel & Thijssen, 1992). The pathogen is both residue and seed borne and can disperse long distance via wheat germplasm exchange (Tillman et al, 1999). Identification and characterization of sources of BLS resistance in wheat would be a vital step in the development of BLS resistant wheat cultivars
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