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Fusarium head blight (FHB) is a destructive wheat disease present throughout the world, and host resistance is an effective and economical strategy used to control FHB. Lack of adequate resistance resource is still a main bottleneck for FHB genetics and wheat breeding research. The synthetic-derived bread wheat line C615, which does not carry the Fhb1 gene, is a promising source of FHB resistance for breeding. A population of 198 recombinant inbred lines (RILs) produced by crossing C615 with the susceptible cultivar Yangmai 13 was evaluated for FHB response using point and spray inoculations. As the disease phenotype is frequently complicated by other agronomic traits, we used both traditional and multivariate conditional QTL mapping approaches to investigate the genetic relationships (at the individual QTL level) between FHB resistance and plant height (PH), spike compactness (SC), and days to flowering (FD). A linkage map was constructed from 3,901 polymorphic SNP markers, which covered 2,549.2 cM. Traditional and conditional QTL mapping analyses found 13 and 22 QTL for FHB, respectively; 10 were identified by both methods. Among these 10, three QTL from C615 were detected in multiple years; these QTL were located on chromosomes 2AL, 2DS, and 2DL. Conditional QTL mapping analysis indicated that, at the QTL level, SC strongly influenced FHB in point inoculation; whereas PH and SC contributed more to FHB than did FD in spray inoculation. The three stable QTL (QFhbs-jaas.2AL, QFhbp-jaas.2DS, and QFhbp-jaas.2DL) for FHB were partly affected by or were independent of the three agronomic traits. The QTL detected in this study improve our understanding of the genetic relationships between FHB response and related traits at the QTL level and provide useful information for marker-assisted selection for the improvement of FHB resistance in breeding.

The powdery mildew resistance gene Pm21 was physically and comparatively mapped by newly developed markers. Seven candidate genes were verified to be required for Pm21 -mediated resistance to wheat powdery mildew. Pm21, a gene derived from wheat wild relative Dasypyrum villosum, has been transferred into common wheat and widely utilized in wheat resistance breeding for powdery mildew. Previously, Pm21 has been located to the bin FL0.45-0.58 of 6VS by using deletion stocks. However, its fine mapping is still a hard work. In the present study, 30 gene-derived 6VS-specific markers were obtained based on the collinearity among genomes of Brachypodium distachyon, Oryza and Triticeae, and then physically and comparatively mapped in the bin FL0.45-0.58 and its nearby chromosome region. According to the maps, the bin FL0.45-0.58 carrying Pm21 was closely flanked by the markers 6VS-03 and 6VS-23, which further narrowed the orthologous regions to 1.06 Mb in Brachypodium and 1.38 Mb in rice, respectively. Among the conserved genes shared by Brachypodium and rice, four serine/threonine protein kinase genes (DvMPK1, DvMLPK, DvUPK and DvPSYR1), one protein phosphatase gene (DvPP2C) and two transcription factor genes (DvGATA and DvWHY) were confirmed to be required for Pm21-mediated resistance to wheat powdery mildew by barley stripe mosaic virus-induced gene silencing (BSMV-VIGS) and transcriptional pattern analyses. In summary, this study gives new insights into the genetic basis of the Pm21 locus and the disease resistance pathways mediated by Pm21.

Pm21, originating from wheat wild relative Dasypyrum villosum, confers immunity to all known races of Blumeria graminis f. sp. tritici (Bgt) and has been widely utilized in wheat breeding. However, little is known on the genetic basis of the Pm21 locus. In the present study, four seedling-susceptible D. villosum lines (DvSus-1 ∼ DvSus-4) were identified from different natural populations. Based on the collinearity among genomes of Brachypodium distachyon, Oryza, and Triticeae, a set of 25 gene-derived markers were developed declaring the polymorphisms between DvRes-1 carrying Pm21 and DvSus-1. Fine genetic mapping of Pm21 was conducted by using an extremely large F2 segregation population derived from the cross DvSus-1/DvRes-1. Then Pm21 was narrowed to a 0.01-cM genetic interval defined by the markers 6VS-08.4b and 6VS-10b. Three DNA markers, including a resistance gene analog marker, were confirmed to co-segregate with Pm21. Moreover, based on the susceptible deletion line Y18-S6 induced by ethyl methanesulfonate treatment conducted on Yangmai 18, Pm21 was physically mapped into a similar interval. Comparative analysis revealed that the orthologous regions of the interval carrying Pm21 were narrowed to a 112.5 kb genomic region harboring 18 genes in Brachypodium, and a 23.2 kb region harboring two genes in rice, respectively. This study provides a high-density integrated map of the Pm21 locus, which will contribute to map-based cloning of Pm21.

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Sharp eyespot is a major fungal disease of wheat caused by Rhizoctonia cerealis in cool and humid environments worldwide. In this study, 224 single seed descent derived F13, F14 and F15 recombinant inbred lines (RILs) from the cross between CI12633 (a resistant cultivar) and Yangmai 9 (a susceptible cultivar) were assessed for sharp eyespot resistance (R.cerealis isolate R0301) in field and greenhouse conditions in three growing seasons. Different agronomic characteristics were also evaluated in the field with no disease infection. All the lines were genotyped with the Illumina iSelect 90 K SNP wheat chip and 101 SSR markers. Sharp eyespot resistance was significantly negatively correlated with heading date and tiller angle, and significantly positively correlated with the diameter of the basal first internode and second internode. Five QTL with a likelihood of odds ratio score of higher than 3.0 were detected on chromosomes 2BS, 4BS, 5AL and 5BS, respectively. These identified QTL may be used in future wheat breeding programs through marker assisted selection for developing sharp eyespot resistant cultivars.

Background: Fusarium head blight (FHB), primarily caused by Fusarium graminearum, is a major threat to wheat production and food security worldwide. Breeding stably and durably resistant cultivars is the most effective approach for managing and controlling the disease. The success of FHB resistance breeding relies on identification of an effective resistant germplasm. We conducted a genome-wide association study (GWAS) using the highdensity wheat 90 K single nucleotide polymorphism (SNP) assays to better understand the genetic basis of FHB resistance in natural population and identify associated molecular markers.Results: The resistance to FHB fungal spread along the rachis (Type II resistance) was evaluated on 171 wheat cultivars in the 2016-2017 (abbr. as 2017) and 2017-2018 (abbr. as 2018) growing seasons. Using Illumina Infinum iSelect 90 K SNP genotyping data, a genome-wide association study (GWAS) identified 26 loci (88 marker-trait associations), which explained 6.65-14.18% of the phenotypic variances. The associated loci distributed across all chromosomes except 2D, 6A, 6D and 7D, with those on chromosomes 1B, 4A, 5D and 7A being detected in both years. New loci for Type II resistance were found on syntenic genomic regions of chromsome 4AL (QFhb-4AL, 621.85-622.24 Mb) and chromosome 5DL (QFhb-5DL, 546.09-547.27 Mb) which showed high collinearity in gene content and order. SNP markers wsnp_JD_c4438_5568170 and wsnp_CAP11_c209_198467 of 5D, reported previously linked to a soil-borne wheat mosaic virus (SBWMV) resistance gene, were also associated with FHB resistance in this study. Conclusion: The syntenic FHB resistant loci and associated SNP markers identified in this study are valuable for FHB resistance breeding via marker-assisted selection.

The SGT1 protein is essential for R protein-mediated and PAMPs-triggered resistance in many plant species. Here we reported the isolation and characterization of the Hv-SGT1 gene from Haynaldia villosa (2n = 14, VV). Analysis of the subcellular location of Hv-SGT1 by transient expression of a fusion to GFP indicated its presence in the cytoplasm and nucleus. Levels of Hv-SGT1 transcripts were increased by inoculation with either the biotrophic pathogen Blumeria graminis DC. f. Sp. tritici (Bgt) or the hemi-biotrophic pathogen Fusarium graminearum (Fg). Levels of Hv-SGT1 showed substantial increase following treatment with H2O2 and methyl jasmonate (MeJA), only slightly induced following exposure to ethephon or abscisic acid, but not changed following exposure to salicylic acid. The demonstration that silencing of Hv-SGT1 substantially reduced resistance to Bgt indicated that Hv-SGT1 was an essential component of disease resistance in H . villosa . The over-expression of Hv-SGT1 in Yangmai 158 enhanced resistance to powdery mildew, and this correlated with increased levels of whole-cell reactive oxygen intermediates at the sites of penetration by the pathogens. Compared with wild-type plants, the expression levels of genes related to the H2O2 and JA signaling pathways were lower in the Hv-SGT1 silenced plants and higher in the Hv-SGT1 over-expressing plants. Therefore, the involvement of Hv-SGT1 in H2O2 production correlates with the hypersensitive response and jasmonic acid signaling. Our novel demonstration that wheat with over-expressed Hv-SGT1 showed enhanced resistance to both powdery mildew and FHB suggests that it could served as a transgenic genetic resource in wheat breeding for multiple disease resistance.