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The durum wheat line DT696 is a source of moderate Fusarium head blight (FHB) resistance. Previous analysis using a bi-parental population identified two FHB resistance quantitative trait loci (QTL) on chromosome 5A: 5A1 was co-located with a plant height QTL, and 5A2 with a major maturity QTL. A Genome-Wide Association Study (GWAS) of DT696 derivative lines from 72 crosses based on multi-environment FHB resistance, plant height, and maturity phenotypic data was conducted to improve the mapping resolution and further elucidate the genetic relationship of height and maturity with FHB resistance. The Global Tetraploid Wheat Collection (GTWC) was exploited to identify durum wheat lines with DT696 allele and additional recombination events. The 5A2 QTL was confirmed in the derivatives, suggesting the expression stability of the 5A2 QTL in various genetic backgrounds. The GWAS led to an improved mapping resolution rendering the 5A2 interval 10 Mbp shorter than the bi-parental QTL mapping interval. Haplotype analysis using SNPs within the 5A2 QTL applied to the GTWC identified novel haplotypes and recombination breakpoints, which could be exploited for further improvement of the mapping resolution. This study suggested that GWAS of derivative breeding lines is a credible strategy for improving mapping resolution.

Background Fusarium head blight (FHB) resistance in the durum wheat breeding gene pool is rarely reported. Triticum turgidum ssp. carthlicum line Blackbird is a tetraploid relative of durum wheat that offers partial FHB resistance. Resistance QTL were identified for the durum wheat cv. Strongfield × Blackbird population on chromosomes 1A, 2A, 2B, 3A, 6A, 6B and 7B in a previous study. The objective of this study was to identify the defense mechanisms underlying the resistance of Blackbird and report candidate regulator defense genes and single nucleotide polymorphism (SNP) markers within these genes for high-resolution mapping of resistance QTL reported for the durum wheat cv. Strongfield/Blackbird population. Results Gene network analysis identified five networks significantly (P Fusarium graminearum-inoculated and mock-inoculated plants, supporting their involvement in constitutive defense. The candidate regulator genes have been implicated in various layers of plant defense including pathogen recognition (mainly Nucleotide-binding Leucine-rich Repeat proteins), signaling pathways including the abscisic acid and mitogen activated protein (MAP) kinase, and downstream defense genes activation including transcription factors (mostly with dual roles in defense and development), and cell death regulator and cell wall reinforcement genes. The expression of five candidate genes measured by quantitative real-time PCR was correlated with that of RNA-seq, corroborating the technical and analytical accuracy of RNA-sequencing. Conclusions Gene network analysis allowed identification of candidate regulator genes and genes associated with constitutive resistance, those that will not be detected using traditional differential expression analysis. This study also shed light on the association of developmental traits with FHB resistance and partially explained the co-localization of FHB resistance with plant height and maturity QTL reported in several previous studies. It also allowed the identification of candidate hub genes within the interval of three previously reported FHB resistance QTL for the Strongfield/Blackbird population and associated SNPs for future high resolution mapping studies.

Breeding for Fusarium head blight (FHB) resistance in durum wheat is complicated by the quantitative trait expression and narrow genetic diversity of available resources. High-density mapping of the FHB resistance quantitative trait loci (QTL), evaluation of their co-localization with plant height and maturity QTL and the interaction among the identified QTL are the objectives of this study. Two doubled haploid (DH) populations, one developed from crosses between Triticum turgidum ssp. durum lines DT707 and DT696 and the other between T. turgidum ssp. durum cv. Strongfield and T. turgidum ssp. carthlicum cv. Blackbird were genotyped using the 90K Infinium iSelect chip and evaluated phenotypically at multiple field FHB nurseries over years. A moderate broad-sense heritability indicated a genotype-by-environment interaction for the expression of FHB resistance in both populations. Resistance QTL were identified for the DT707 × DT696 population on chromosomes 1B, 2B, 5A (two loci) and 7A and for the Strongfield × Blackbird population on chromosomes 1A, 2A, 2B, 3A, 6A, 6B and 7B with the QTL on chromosome 1A and those on chromosome 5A being more consistently expressed over environments. FHB resistance co-located with plant height and maturity QTL on chromosome 5A and with a maturity QTL on chromosome 7A for the DT707 × DT696 population. Resistance also co-located with plant height QTL on chromosomes 2A and 3A and with maturity QTL on chromosomes 1A and 7B for the Strongfield × Blackbird population. Additive × additive interactions were identified, for example between the two FHB resistance QTL on chromosome 5A for the DT707 × DT696 population and the FHB resistance QTL on chromosomes 1A and 7B for the Strongfield × Blackbird population. Application of the Single Nucleotide Polymorphic (SNP) markers associated with FHB resistance QTL identified in this study will accelerate combining genes from the two populations.

The aim of this study was to verify that wheat seedlings treated with Pseudomonas fluorescens CHA0 (CHA0 hereafter) before inoculation with Gaeumannomyces graminis var. tritici (Ggt), a pathogen of take-all, acquire induced resistance to Ggt. The soil with wheat seedlings growing on it was drenched with a suspension of CHA0 cells and inoculated with Ggt 24 h later. Then, the seedlings were grown in a glasshouse, and severity of take-all disease, fresh weights of root and shoot and lengths of root and shoot, and also the activities of soluble peroxidase (SPOX), ionically cell-wall-bound peroxidase (CWPOX), β-1,3-glucanase, β-1,4-glucanase and the concentration of total phenolic compounds in the root of the seedlings were examined. The results indicated that the treatment with CHA0 before inoculation with Ggt mitigated the disease severity significantly, and increased the root and shoot lengths and root and shoot fresh weights. The treatment with CHA0 increased the activities of SPOX, CWPOX, β-1-3-glucanase, β-1,4-glucanase and phenolic compounds in the wheat roots and the activities of SPOX and β-1,4-glucansee activities were highest at day 4 and those of CWPOX and β-1,3-glucanase at day 6 after inoculation with Ggt. The concentration of total phenolic compounds was also highest at day 6 after the inoculation with Ggt. The results suggest that the take-all suppressing effect of CHA0 may be related to enhanced defense response of the wheat roots.

The aim of this study was to verify that induced resistance was another mechanism through which Bacillus pumilus 7 km can suppress Gaeumannomyces graminis (Sacc.) Von Arx and Oliver var. tritici Walker (Ggt). Also, plant growth-promotion activity of B. pumilus 7 km and its effect on disease severity of take-all were evaluated. Soil was drenched with B. pumilus 7 km and disease severity, root and shoot fresh weights and root and shoot heights were evaluated. The activities of soluble peroxidase (SPOX), ionically cell wall-bound peroxidase (CWPOX), β-1,3-glucanase, β-1,4-glucanase and the contents of total phenolic compounds were also determined. The results indicated that disease severity in the bacterized roots was significantly less than the pathogen control roots. Also this isolate promoted root height, root and shoot fresh weights, compared with the healthy control plants. Wheat plants treated with B. pumilus 7 km showed increased presence of SPOX, CWPOX, β-1,3-glucanase, β-1,4-glucanase and phenolic compounds in bacterized roots challenged with the pathogen. In this treatment, maximum SPOX, β-1,3-glucanase and β-1,4-glucanase activities on day 4 and CWPOX activity on day 8 were recorded. Also, maximum total phenolic concentration on day 6 was recorded. The results suggest that the inhibitory effect of B. pumilus 7 km on the take-all may be related to its ability to enhance defense responses in the wheat roots.