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Leaf rust, caused by Puccinia triticina (Pt), is a major disease of wheat and a significant problem for wheat production in Brazil. The Brazilian variety Toropi, released in 1965, has maintained high levels of field, adult plant resistance (APR) to leaf rust across global locations, while microscopic studies have indicated prehaustorial resistance mechanisms. Analyses of gene expression in flag leaves of Toropi, during the early stages of Pt infection, were undertaken to explore the mechanisms behind the APR in Toropi. Differential expression of wheat genes was undertaken, comparing Pt‐ to mock‐inoculated and Pt‐ to Pt‐inoculated time points. Analysis of gene expression indicated a strong response to Pt, which was fully active by 6 h after inoculation (hai). More genes were downregulated than upregulated, particularly at 6 and 12 hai. Gene Ontology enrichment analysis indicated a shutting down of RNA and protein synthesis and an early effect on photosynthesis, with disruption of the electron transfer chain. Analyses of upregulated genes identified genes involved in ATP‐binding and protein kinase activity at 6 hai, supporting a rapid metabolic response to Pt infection. A general upregulation of genes involved in transport and metabolism indicated the need to relocate protein and organic‐based resources. Alignment of differentially expressed genes with the genomic regions defining four leaf rust APR quantitative trait loci (QTLs) in Toropi identified candidate resistance genes, including a sugar transporter, a receptor kinase and a seven‐transmembrane MLO family protein. In addition, 60 Pt genes were identified, 11 being annotated as potential effector proteins. [ABSTRACT FROM AUTHOR]

Wheat stripe mosaic virus (WhSMV) is the causal agent of soilborne wheat mosaic disease (SBWMD) in Brazil, which is a serious threat to wheat production in the southern part of the country. WhSMV also occurs in Paraguay and South Africa. The virus is soilborne, transmitted by Polymyxa graminis, and management strategies are mainly based on genetic resistance. Variation in the reaction (type and severity of symptoms) of cultivars has been reported depending on the region and/or year of cultivation, leading wheat breeding programmes to test their materials in several locations, which increases costs and is time‐consuming. One hypothesis is that this variation in symptoms is a result of the genetic variability of WhSMV. We assessed the genetic variability and population structure of WhSMV infecting wheat in Brazil and South Africa. In field experiments conducted in different locations in southern Brazil, a consistent reproducibility of symptoms was observed in a set of cultivars, and molecular analysis showed a low degree of genetic variability of the Brazilian viral population. The hypothesis that the variation in SBWMD symptoms in Brazil is due to genetic variability of the virus was thus rejected. Comparison of the Brazilian and South African WhSMV isolates indicated that they comprise distinct subpopulations and that the Brazilian subpopulation is more variable than the South African subpopulation. The lower genetic variability of the South African subpopulation suggests genetic stability or a recent emergence of WhSMV in that region. [ABSTRACT FROM AUTHOR]

Fungicides play an important role in wheat blast management in Brazil. To determine whether the reported patterns of fungicide resistance are present in Pyricularia oryzae populations from wheat and signal grass grown in Minas Gerais state, Brazil, we characterized the sensitivity of a contemporary collection (2018 and 2019) of 64 fungal isolates to seven fungicides belonging to DMI (tebuconazole and epoxiconazole), QoI (azoxystrobin and pyraclostrobin) and SDHI (bixafen, fluxapyroxad and benzovindiflupyr) groups. We further assessed if the differential sensitivity of selected isolates affected disease control using commercial doses of the fungicides applied protectively (prior to inoculation) on the heads of potted plants. Despite finding relatively low levels of in vitro sensitivity to some of the fungicides (e.g., azoxystrobin, fluxapyroxad and bixafen), control efficacies (percentage reductions in head blast severity) were significantly higher than the untreated plants and not affected by the sensitivity of the strain to all fungicides but azoxystrobin. The levels of head blast control for some of the fungicides (>70%) in the greenhouse were similar to or higher than previously reported in the field. The molecular data for a set of isolates representing different fungicide sensitivity levels were generally not predictive of the phenotype. The wheat‐infecting isolates were less sensitive than signal grass‐infecting isolates to all fungicides including azoxystrobin. Our study not only confirms previous reports of low sensitivity to some fungicides, but it also suggests options among site‐specific fungicides, most notably tebuconazole and benzovindiflupyr, that can still be used under an antiresistance strategy such as coformulation with multisite fungicides. [ABSTRACT FROM AUTHOR]

Wheat farmers rely on fungicides to protect fields against several foliar and flowering diseases, including Fusarium head blight (FHB). A range of active ingredients is used in isolation or in dual premixes that include a dimethylation inhibitor (DMI) or a quinone outside inhibitor (QoI) fungicide. Comprehensive information about fungicide resistance in F. graminearum is available for DMIs, while for QoIs the data are scarce. We characterized 225 strains obtained from two states in southern Brazil, Rio Grande do Sul (RS) and Paraná (PR), in relation to their response to two QoIs. The median EC50 (effective concentration leading to 50% inhibition of conidial germination) value for azoxystrobin (n = 25 isolates) was 2.20 μg/ml in the PR population and 4.04 μg/ml in the RS population. For pyraclostrobin (n = 50), the median EC50 was 0.28 μg/ml in the PR population and 0.24 μg/ml in the RS population. Evidence of cross‐resistance could not be detected. Screening using a discriminatory dose (DD) for azoxystrobin in a larger number of isolates from PR (n = 75) and RS (n = 100) states allowed the detection of 50% and 28% sensitive strains, respectively. Using the DD for pyraclostrobin, 33% and 18.8% were classified as less sensitive in the PR and RS isolates, respectively. In RS, the frequency of less‐sensitive isolates increased over time (2007–2011). No point mutation at any of the target spots (F129L, G137R, G143A) was detected. Our results represent an important step towards the establishment of a sensitivity profile for two of the most commonly used QoIs in commercial premixes targeting FHB control. [ABSTRACT FROM AUTHOR]

Fungicides have not been effective in controlling the wheat blast disease in Brazil. An earlier analysis of 179 isolates of Pyricularia oryzae Triticum lineage (PoTl) sampled from wheat fields across six populations in central‐southern Brazil during 2012 discovered a high level of resistance to strobilurin fungicides. Here we analysed azole resistance in the same strains based on EC50 measurements for tebuconazole and epoxiconazole. All six Brazilian populations of PoTl exhibited high resistance to both azoles, with in vitro EC50 values that were at least 35 to 50 times higher than the recommended field doses. We sequenced the CYP51A and CYP51B genes to determine if they were likely to play a role in the observed azole resistance. Although we found five distinct haplotypes in PoTl carrying four nonsynonymous substitutions in CYP51A, none of these substitutions were correlated with elevated EC50. CYP51B was sequenced for nine PoTl isolates, three each representing low, medium, and high tebuconazole EC50. Both PoTl CYP51A and CYP51B could complement yeast CYP51 function. All PoTl CYP51A‐expressing yeast transformants were less sensitive to triazoles than the PoTl CYP51B ones. Transformants expressing PoTl CYP51A haplotype H1 carrying the R158K substitution were not more resistant than those expressing PoTl CYP51A haplotype H5, which is synonymous to haplotype H6, found in triazole‐sensitive P. oryzae Oryza isolates from rice blast. Therefore, the reduced triazole sensitivity of wheat blast isolates compared to rice blast isolates appears to be associated with a non‐target‐site related resistance mechanism acquired after higher exposure to triazoles. [ABSTRACT FROM AUTHOR]

We conducted a five‐year survey (2011–2015) of barley and wheat fields in Paraná state, Brazil, obtaining 754 Fusarium isolates from spikes with fusarium head blight (FHB)‐symptoms. Multilocus genotyping and TEF‐1α gene sequence analyses confirmed the dominance of the F. graminearum species complex (FGSC, 75.7%), but F. poae (11.5%), as well as F. avenaceum and related members of the F. tricinctum species complex (FTSC, 8.1%) appeared as substantial contributors to FHB. Within the FGSC, F. graminearum of the 15‐ADON genotype was dominant (63%), followed by F. meridionale of the NIV genotype (23.1%), F. cortaderiae of the NIV (7%) or 3‐ADON (2.6%) genotypes, and F. austroamericanum (3.8%) of the 3‐ADON genotype. Substantial variation in pathogen composition was observed across years, with F. poae and F. meridionale frequencies significantly elevated in some years. Most F. poae strains produced DAS, diANIV, and butenolide, but not neosolaniol, T‐2, or HT‐2. All FTSC species produced moniliformin. Enniatin production was widespread among FTSC species, with the single F. acuminatum strain found to be the strongest producer of enniatins. Our findings confirm FGSC as a major contributor to FHB and expand considerably our knowledge of the presence, frequency, and conditions under which other pathogens may emerge, altering the spectrum of toxins that may accumulate in grain. [ABSTRACT FROM AUTHOR]