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2.
Phytopathology ; 113(10): 1979-1984, 2023 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-37160671

RESUMO

Powdery mildew is caused by the highly adaptive biotrophic fungus Blumeria graminis f. sp. tritici infecting wheat worldwide. Novel powdery mildew resistance genes are urgently needed that can be used rapidly in wheat cultivar development with minimal disruption of trait advances elsewhere. PI 351817 is a German cultivar exhibiting a wide spectrum of resistance to B. graminis f. sp. tritici isolates collected from different wheat-growing regions of the United States. Evaluation of an F2 population and 237 F2:3 lines derived from OK1059060-2C14 × PI 351817 for responses to B. graminis f. sp. tritici isolate OKS(14)-B-3-1 identified a single dominant gene, designated Pm351817, for powdery mildew resistance in PI 351817. Using bulked segregant analysis (BSA) and simple sequence repeat (SSR) markers, Pm351817 was mapped in the terminal region of the long arm of chromosome 2A. Deep sequencing of the genotyping-by-sequencing libraries of the two parental lines identified a set of single-nucleotide polymorphism (SNP) markers in the 2AL candidate gene region. Those SNP markers was subsequently converted to Kompetitive allele-specific PCR (KASP) markers for genotyping the mapping population. Linkage analysis delimited Pm351817 to a 634-kb interval between Stars-KASP656 (771,207,512 bp) and Stars-KASP662 (771,841,609 bp) on 2AL, based on the Chinese Spring reference sequence IWGSC RefSeq v 2.1. Tests of allelism indicated that Pm351817 is located at the Pm65 locus. Pm351817 shows resistance to all B. graminis f. sp. tritici isolates used in this study and can be used to enhance powdery mildew resistance in the United States. KASP markers flanking Pm351817 can be used to select Pm351817 in wheat breeding programs after further tests for polymorphism.


Assuntos
Resistência à Doença , Triticum , Mapeamento Cromossômico , Triticum/genética , Triticum/microbiologia , Marcadores Genéticos , Alelos , Resistência à Doença/genética , Melhoramento Vegetal , Genes de Plantas/genética , Doenças das Plantas/microbiologia , Erysiphe
3.
Phytopathology ; 113(10): 1898-1907, 2023 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-37147578

RESUMO

Septoria nodorum blotch (SNB), caused by Parastagonospora nodorum, is a major disease of winter wheat that occurs frequently in the central and southeastern United States. Quantitative resistance to SNB in wheat is determined by various disease resistance components and their interaction with environmental factors. A study was conducted in North Carolina from 2018 to 2020 to characterize SNB lesion size and growth rate and to quantify the effects of temperature and relative humidity on lesion expansion in winter wheat cultivars with different levels of resistance. Disease was initiated in the field by spreading P. nodorum-infected wheat straw in experimental plots. Cohorts (groups of foliar lesions arbitrarily selected and tagged as an observational unit) were sequentially selected and monitored throughout each season. Lesion area was measured at regular intervals, and weather data were collected using in-field data loggers and the nearest weather stations. Final mean lesion area was approximately seven times greater on susceptible than on moderately resistant cultivars, and lesion growth rate was approximately four times higher on susceptible than on moderately resistant cultivars. Across trials and cultivars, temperature had a strong effect of increasing lesion growth rates (P < 0.001), while relative humidity had no significant effect (P = 0.34). Lesion growth rate declined slightly and steadily over the duration of cohort assessment. Our results demonstrate that restricting lesion growth is an important component of SNB resistance in the field and suggest that the ability to limit lesion size may be a useful breeding goal.


Assuntos
Doenças das Plantas , Triticum , Humanos , Estações do Ano , Melhoramento Vegetal , Tempo (Meteorologia) , North Carolina
4.
Plant Dis ; 107(7): 2054-2060, 2023 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-37039843

RESUMO

Fusarium head blight (FHB) is among the chief threats to profitable barley production, and fungicide applications are one of two main strategies for reducing FHB damage to barley crops. However, there is very little published information on optimal timing of such applications. A 4-year field study was conducted with winter barley in Raleigh, North Carolina, to compare three timings for fungicide application: 50% spike emergence (Zadoks growth stage or GS 55), 100% spike emergence (GS 59), and 6 days after GS 59. Three winter barley cultivars with varying levels of FHB resistance were grown for four successive years (2018 to 2021) in a split-plot experiment and inoculated each spring with Fusarium-infected corn spawn. Three fungicides were compared: propiconazole + pydiflumetofen (Miravis Ace), prothioconazole + tebuconazole (Prosaro), and metconazole (Caramba). Correlations among visual symptoms and assays of harvested grain were modest and were weakened by fungicide applications. Across years and cultivars, deoxynivalenol (DON) and percent Fusarium-infected kernels were most reduced relative to the nontreated control by fungicide applications at the latest timing (GS 59 + 6 days). The early (GS 55) timing resulted in DON not significantly different from the nontreated control. Based on these results, it is recommended that to minimize damage from FHB, fungicide should be applied to winter barley several days after GS 59 (100% spike emergence), and not before GS 59.


Assuntos
Fungicidas Industriais , Fusarium , Hordeum , Fungicidas Industriais/farmacologia , Doenças das Plantas/prevenção & controle , Triticum
5.
New Phytol ; 238(4): 1546-1561, 2023 05.
Artigo em Inglês | MEDLINE | ID: mdl-36772855

RESUMO

Blumeria graminis f. sp. tritici (Bgt) is a globally important fungal pathogen of wheat that can rapidly evolve to defeat wheat powdery mildew (Pm) resistance genes. Despite periodic regional deployment of the Pm1a resistance gene in US wheat production, Bgt strains that overcome Pm1a have been notably nonpersistent in the United States, while on other continents, they are more widely established. A genome-wide association study (GWAS) was conducted to map sequence variants associated with Pm1a virulence in 216 Bgt isolates from six countries, including the United States. A virulence variant apparently unique to Bgt isolates from the United States was detected in the previously mapped gene AvrPm1a (BgtE-5612) on Bgt chromosome 6; an in vitro growth assay suggested no fitness reduction associated with this variant. A gene on Bgt chromosome 8, Bgt-51526, was shown to function as a second determinant of Pm1a virulence, and despite < 30% amino acid identity, BGT-51526 and BGTE-5612 were predicted to share > 85% of their secondary structure. A co-expression study in Nicotiana benthamiana showed that BGTE-5612 and BGT-51526 each produce a PM1A-dependent hypersensitive response. More than one member of a B. graminis effector family can be recognized by a single wheat immune receptor, and a two-gene model is necessary to explain virulence to Pm1a.


Assuntos
Estudo de Associação Genômica Ampla , Triticum , Triticum/microbiologia , Virulência/genética , Doenças das Plantas/microbiologia , Resistência à Doença/genética
6.
Plant Dis ; 107(4): 1122-1130, 2023 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-36131496

RESUMO

Prediction models that aid growers in making decisions on timing of fungicide application are important components of integrated management programs for several foliar diseases of wheat. The risk of Septoria nodorum blotch (caused by Parastagonospora nodorum) onset in winter wheat has been reported to be influenced by location, amount of wheat residue in the field, and cumulative daily infection values 2 weeks prior to day of year (DOY) 102. A model previously developed based on these predictor variables was evaluated for its ability to predict disease onset under field conditions. An experiment was conducted at three locations in North Carolina in 2018, 2019, and 2020, where plots were either treated with >20% wheat residue or received no residue treatment. Plots were monitored for disease symptoms, and disease onset was defined to have occurred when mean disease incidence in a plot was 50%. Of the 298 disease cases recorded, disease onset occurred early (i.e., prior to DOY 102) in 257 cases, while onset was late (i.e., on or after DOY 102) in 41 cases. Model accuracy based on correct classification ranged from 0.67 to 0.95, with a mean of 0.87 across the study period. Similarly, sensitivity rates of the model ranged from 0.88 to 1.0 with a mean of 0.98 across all years. However, the model had low specificity, with a mean rate of 0.15 across the study period. Overall, there was no significant difference in the frequency of observed and predicted cases in the study (χ2 = 0.50, P = 0.7788, df = 2). Time to disease onset was significantly correlated with grain yield and explained 26% of variation in yield (P < 0.0001). Results indicated that the disease onset model performs well in predicting early disease onset but requires further evaluation and improvement, particularly in the Piedmont, where it over-predicted early onset in 2 successive years.


Assuntos
Ascomicetos , Triticum , Doenças das Plantas , Estações do Ano
8.
Nat Commun ; 13(1): 4315, 2022 07 26.
Artigo em Inglês | MEDLINE | ID: mdl-35882860

RESUMO

The fungus Blumeria graminis f. sp. tritici causes wheat powdery mildew disease. Here, we study its spread and evolution by analyzing a global sample of 172 mildew genomes. Our analyses show that B.g. tritici emerged in the Fertile Crescent during wheat domestication. After it spread throughout Eurasia, colonization brought it to America, where it hybridized with unknown grass mildew species. Recent trade brought USA strains to Japan, and European strains to China. In both places, they hybridized with local ancestral strains. Thus, although mildew spreads by wind regionally, our results indicate that humans drove its global spread throughout history and that mildew rapidly evolved through hybridization.


Assuntos
Doenças das Plantas , Triticum , Genômica , Migração Humana , Humanos , Doenças das Plantas/microbiologia , Poaceae , Triticum/genética , Triticum/microbiologia
9.
J Sci Food Agric ; 102(14): 6358-6372, 2022 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-35535556

RESUMO

BACKGROUND: Fusarium poae is one of the most common Fusarium head blight (FHB) causal agents in wheat. This species can biosynthesize a wide range of mycotoxins, in particular nivalenol (NIV). In FHB epidemiology, infection timing is important for disease occurrence, kernel development, symptom appearance and mycotoxin accumulation in grain. The present study explored, both in a controlled environment and in a 2-year field plot experiment in Central Italy, the influence of five infection timings (from beginning of flowering to medium milk growth stage) on F. poae colonization and mycotoxin accumulation in bread wheat spikes (spring cv. A416 and winter cv. Ambrogio). RESULTS: Both climate chamber and field experiments showed that early infection timings (from beginning of flowering to full flowering) especially favoured F. poae colonization and accumulation of its mycotoxins (particularly NIV) in grain. By contrast, later infection timings (watery ripe and medium milk) reduced F. poae development and mycotoxin levels. The time window of host susceptibility in the field was shorter than that observed under controlled conditions. Symptom expression in kernels also differed among infection timings. In general, F. poae biomass was higher in the chaff than in the grain. CONCLUSION: These results enhance knowledge of a common member of the FHB complex worldwide, and could be useful in forecasting the risk of F. poae infection and mycotoxin contamination. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.


Assuntos
Fusarium , Micotoxinas , Pão , Grão Comestível/química , Micotoxinas/análise , Doenças das Plantas , Tricotecenos , Triticum/metabolismo
10.
PLoS One ; 17(5): e0268546, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35588401

RESUMO

In humid and temperate areas, Septoria nodorum blotch (SNB) is a major fungal disease of common wheat (Triticum aestivum L.) in which grain yield is reduced when the pathogen, Parastagonospora nodorum, infects leaves and glumes during grain filling. Foliar SNB susceptibility may be associated with sensitivity to P. nodorum necrotrophic effectors (NEs). Both foliar and glume susceptibility are quantitative, and the underlying genetics are not understood in detail. We genetically mapped resistance quantitative trait loci (QTL) to leaf and glume blotch using a double haploid (DH) population derived from the cross between the moderately susceptible cultivar AGS2033 and the resistant breeding line GA03185-12LE29. The population was evaluated for SNB resistance in the field in four successive years (2018-2021). We identified major heading date (HD) and plant height (PH) variants on chromosomes 2A and 2D, co-located with SNB escape mechanisms. Five QTL with small effects associated with adult plant resistance to SNB leaf and glume blotch were detected on 1A, 1B, and 6B linkage groups. These QTL explained a relatively small proportion of the total phenotypic variation, ranging from 5.6 to 11.8%. The small-effect QTL detected in this study did not overlap with QTL associated with morphological and developmental traits, and thus are sources of resistance to SNB.


Assuntos
Locos de Características Quantitativas , Triticum , Ascomicetos , Resistência à Doença/genética , Fenótipo , Melhoramento Vegetal , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Locos de Características Quantitativas/genética , Triticum/genética , Triticum/microbiologia
11.
Phytopathology ; 112(2): 249-260, 2022 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-34156265

RESUMO

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is managed primarily with cultivar resistance and foliar fungicides. Quinone outside inhibitors (QoIs), which target the mitochondrial cytochrome b (cytb) gene, are one of the two main fungicide classes used on wheat. While European populations of B. graminis f. sp. tritici are widely insensitive to QoIs, largely because of the cytb mutation G143A, the QoI sensitivity of the U.S. B. graminis f. sp. tritici population had never been evaluated despite years of QoI use on U.S. wheat. A total of 381 B. graminis f. sp. tritici isolates from 15 central and eastern U.S. states were screened for sensitivity to QoI fungicides pyraclostrobin and picoxystrobin. A modest range of sensitivities was observed, with maximum resistance factors of 11.2 for pyraclostrobin and 5.3 for picoxystrobin. The F129L, G137R, and G143A cytb mutations were not detected in the U.S. B. graminis f. sp. tritici population, nor were mutations identified in the PEWY loop, a key part of the Qo site. Thus, no genetic basis for the observed quantitative variation in QoI sensitivity of U.S. B. graminis f. sp. tritici was identified. Isolate sporulation was weakly negatively associated with reduced QoI sensitivity, suggesting a fitness cost. In the course of the study, the complete B. graminis f. sp. tritici cytb gene sequence was determined for the first time in the isolate 96224 v. 3.16 reference genome. Contrary to previous reports, the gene has an intron that appears to belong to intron group II, which is unusual in fungi. The study was the first QoI sensitivity screening of a large, geographically diverse set of U.S. B. graminis f. sp. tritici isolates, and while the population as a whole remains relatively sensitive, some quantitative loss of efficacy was observed.


Assuntos
Ascomicetos , Fungicidas Industriais , Ascomicetos/genética , Citocromos b/genética , Fungicidas Industriais/farmacologia , Doenças das Plantas/microbiologia , Estrobilurinas , Triticum/microbiologia
12.
Plant Dis ; 105(4): 986-996, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33210972

RESUMO

In eastern North Carolina, mild to severe stunting and root rot have reduced yields of winter wheat, especially during years with abundant rainfall. Causal agents of root rot of wheat in this region were previously identified as Pythium irregulare, P. vanterpoolii, and P. spinosum. To investigate species prevalence, 114 isolates of Pythium were obtained from symptomatic wheat plants collected in eight counties. Twelve species were recovered, with P. irregulare (32%), P. vanterpoolii (17%), and P. spinosum (16%) the most common. Pathogenicity screens were performed with selected isolates of each species, and slight to severe necrosis of young roots was observed. The aggressiveness of five isolates each of P. irregulare, P. vanterpoolii, and P. spinosum was compared on a single cultivar of wheat at 14°C, and very aggressive isolates were found within all species. In vitro growth of these isolates was measured at 14 and 20°C, and all isolates grew faster at the warmer temperature. The effects of varying temperatures and rates of nitrogen on root rot caused by Pythium spp. alone or in combination were investigated. All inoculation treatments caused severe root rot under all conditions tested, and disease was more severe at 12 and 14°C compared with 18 and 20°C; however, there was no effect of nitrogen application.


Assuntos
Pythium , Transtornos do Crescimento , Humanos , North Carolina , Doenças das Plantas , Triticum
13.
Plant Dis ; 104(11): 2928-2939, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32900293

RESUMO

The duration of wheat susceptibility to Fusarium infection has implications for risk forecasting, fungicide timing, and the likelihood that visible kernel damage may underpredict deoxynivalenol (DON) contamination. A field experiment was conducted to explore the impact of varying infection timings on Fusarium head blight (FHB) development in winter wheat. Trials in four successive years (2010 to 2013) in North Carolina utilized one susceptible and one moderately resistant cultivar possessing similar maturity, stature, and grain quality. Inoculum was applied in the form of sprayed Fusarium graminearum conidia. In the first year, the nine infection timings were from 0 to 21 days after anthesis (daa), whereas in the following 3 years, they ranged from 0 to 13 daa. Infection progression was compared among inoculation timings by sampling spikes five to six times during grain-fill. Based on DON, percent kernel damage and kernel infection, and fungal spread as assayed via qPCR, the moderately resistant cultivar had at least a 2- to 3-day shorter window of susceptibility to damaging FHB infection than the susceptible cultivar. The results suggest that duration of susceptibility is an important aspect of cultivar resistance to FHB. In 2012, the window of susceptibility for both cultivars was extended by cold snaps during anthesis. After debranning in one year, the majority of DON was found to be in the bran fraction of kernels; there was also a trend for later infections to lead to a higher percentage of DON in the nonbran fraction, as well as a higher ratio of DON to FDK.


Assuntos
Fusarium , Tricotecenos , North Carolina , Doenças das Plantas , Triticum
14.
Int J Food Microbiol ; 323: 108594, 2020 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-32229393

RESUMO

Worldwide, while Fusarium graminearum is the main causal species of Fusarium head blight (FHB) in small-grain cereals, a diversity of FHB-causing species belonging to different species complexes has been found in most countries. In the U.S., FHB surveys have focused on the Fusarium graminearum species complex (FGSC) and the frequencies of 3-ADON, 15-ADON, and nivalenol (NIV) chemotypes. A large-scale survey was undertaken across the state of North Carolina in 2014 to explore the frequency and distribution of F. graminearum capable of producing NIV, which is not monitored at grain intake points. Symptomatic wheat spikes were sampled from 59 wheat fields in 24 counties located in three agronomic zones typical of several states east of the Appalachian Mountains: Piedmont, Coastal Plain, and Tidewater. Altogether, 2197 isolates were identified to species using DNA sequence-based methods. Surprisingly, although F. graminearum was the majority species detected, species in the Fusarium tricinctum species complex (FTSC) that produce "emerging mycotoxins" were frequent, and even dominant in some fields. The FTSC percentage was 50-100% in four fields, 30-49% in five fields, 20-29% in five fields, and < 20% in the remaining 45 fields. FTSC species were at significantly higher frequency in the Coastal Plain than in the Piedmont or Tidewater (P < .05). Moniliformin concentrations in samples ranged from 0.0 to 38.7 µg g-1. NIV producing isolates were rare statewide (2.2%), and never >12% in a single field, indicating that routine testing for NIV is probably unnecessary. The patchy distribution of FTSC species in wheat crops demonstrated the need to investigate the potential importance of their mycotoxins and the factors that allow them to sometimes outcompete trichothecene producers. An increased sampling intensity of wheat fields led to the unexpected discovery of a minority FHB-causing population.


Assuntos
Grão Comestível/microbiologia , Fusarium/classificação , Fusarium/fisiologia , Micotoxinas/análise , Micotoxinas/metabolismo , Triticum/microbiologia , Biodiversidade , North Carolina , Doenças das Plantas , Tricotecenos/análise , Tricotecenos/metabolismo
15.
Front Plant Sci ; 11: 155, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32210986

RESUMO

Important advances have been made in understanding the relationship of necrotrophic effectors (NE) and host sensitivity (Snn) genes in the Parastagonospora nodorum-wheat pathosystem. Yet much remains to be learned about the role of these interactions in determining wheat resistance levels in the field, and there is mixed evidence on whether breeding programs have selected against Snn genes due to their role in conferring susceptibility. SNB occurs ubiquitously in the U.S. Atlantic seaboard, and the environment is especially well suited to field studies of resistance to natural P. nodorum populations, as there are no other important wheat leaf blights. Insights into the nature of SNB resistance have been gleaned from multi-year data on phenotypes and markers in cultivars representative of the region's germplasm. In this perspective article, we review the evidence that in this eastern region of the U.S., wheat cultivars have durable quantitative SNB resistance and Snn-NE interactions are of limited importance. This conclusion is discussed in light of the relevant available information from other parts of the world.

16.
Plant Dis ; 104(3): 634-648, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31967505

RESUMO

The main techniques for minimizing Fusarium head blight (FHB, or scab) and deoxynivalenol in wheat and barley are well established and generally available: planting of moderately FHB-resistant cultivars, risk monitoring, and timely use of the most effective fungicides. Yet the adoption of these techniques remains uneven across the FHB-prone portions of the U.S. cereal production area. A national survey was undertaken by the U.S. Wheat and Barley Scab Initiative in 17 states where six market classes of wheat and barley are grown. In 2014, 5,107 usable responses were obtained. The highest percentages reporting losses attributable to FHB in the previous 5 years were in North Dakota, Maryland, Kentucky, and states bordering the Great Lakes but across all states, ≥75% of respondents reported no FHB-related losses in the previous 5 years. Adoption of cultivar resistance was uneven by state and market class and was low except among hard red spring wheat growers. In 13 states, a majority of respondents had not applied an FHB-targeted fungicide in the previous 5 years. Although the primary FHB information source varied by state, crop consultants were considered to be an important source or their primary source of information on risk or management of FHB by the largest percentage of respondents. Use of an FHB risk forecasting website was about twice as high in North Dakota as the 17-state average of 6%. The most frequently cited barriers to adopting FHB management practices were weather or logistics preventing timely fungicide application, difficulty in determining flowering timing for fungicide applications, and the impracticality of FHB-reducing rotations. The results highlight the challenges of managing an episodically damaging crop disease and point to specific areas for improvement.


Assuntos
Fusarium , Hordeum , Kentucky , Maryland , North Dakota , Doenças das Plantas , Inquéritos e Questionários , Triticum
17.
PLoS Genet ; 15(10): e1008223, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31626626

RESUMO

Filamentous fungi rapidly evolve in response to environmental selection pressures in part due to their genomic plasticity. Parastagonospora nodorum, a fungal pathogen of wheat and causal agent of septoria nodorum blotch, responds to selection pressure exerted by its host, influencing the gain, loss, or functional diversification of virulence determinants, known as effector genes. Whole genome resequencing of 197 P. nodorum isolates collected from spring, durum, and winter wheat production regions of the United States enabled the examination of effector diversity and genomic regions under selection specific to geographically discrete populations. 1,026,859 SNPs/InDels were used to identify novel loci, as well as SnToxA and SnTox3 as factors in disease. Genes displaying presence/absence variation, predicted effector genes, and genes localized on an accessory chromosome had significantly higher pN/pS ratios, indicating a higher rate of sequence evolution. Population structure analyses indicated two P. nodorum populations corresponding to the Upper Midwest (Population 1) and Southern/Eastern United States (Population 2). Prevalence of SnToxA varied greatly between the two populations which correlated with presence of the host sensitivity gene Tsn1 in the most prevalent cultivars in the corresponding regions. Additionally, 12 and 5 candidate effector genes were observed to be under diversifying selection among isolates from Population 1 and 2, respectively, but under purifying selection or neutrally evolving in the opposite population. Selective sweep analysis revealed 10 and 19 regions that had recently undergone positive selection in Population 1 and 2, respectively, involving 92 genes in total. When comparing genes with and without presence/absence variation, those genes exhibiting this variation were significantly closer to transposable elements. Taken together, these results indicate that P. nodorum is rapidly adapting to distinct selection pressures unique to spring and winter wheat production regions by rapid adaptive evolution and various routes of genomic diversification, potentially facilitated through transposable element activity.


Assuntos
Ascomicetos/genética , Fungos/genética , Doenças das Plantas/genética , Seleção Genética/genética , Triticum/microbiologia , Aclimatação/genética , Ascomicetos/patogenicidade , Evolução Molecular , Proteínas Fúngicas/genética , Fungos/patogenicidade , Genética Populacional , Genômica , Interações Hospedeiro-Patógeno/genética , Doenças das Plantas/microbiologia , Polimorfismo de Nucleotídeo Único/genética , Locos de Características Quantitativas/genética , Triticum/genética , Triticum/crescimento & desenvolvimento , Fatores de Virulência/genética
18.
Plant Dis ; 103(12): 3108-3116, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31657998

RESUMO

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is managed in the United States with cultivar resistance and foliar fungicides. Despite high levels of fungicide sensitivity in other cereal mildew populations, fungicide sensitivity of U.S. B. graminis f. sp. tritici has never been evaluated. Almost 400 B. graminis f. sp. tritici isolates were collected from 15 U.S. states over 2 years and phenotyped for sensitivity to two widely used demethylation inhibitor (DMI) fungicides, tebuconazole and prothioconazole. A large range of sensitivity to both DMIs was observed, with more insensitive isolates originating from the eastern United States (Great Lakes, Mid-Atlantic, and Southeast regions) and more sensitive isolates from central states (Plains region, Arkansas, and Missouri). Cross-resistance was indicated by a positive although weak association between tebuconazole and prothioconazole sensitivities at all levels of analysis (EC50 values, P < 0.0001). A possible fitness cost was also associated with prothioconazole insensitivity (P = 0.0307) when analyzed at the state population level. This is the first assessment of fungicide sensitivity in the U.S. B. graminis f. sp. tritici population, and it produced evidence of regional selection for reduced DMI efficacy. The observation of reduced sensitivity to DMI fungicides in the eastern United States underlines the importance of rotating between chemistry classes to maintain the effectiveness of DMIs in U.S. wheat production. Although cross-resistance was demonstrated, variability in the relationship of EC50 values for tebuconazole and prothioconazole also suggests that multiple mechanisms influence B. graminis f. sp. tritici isolate responses to these two DMI fungicides.


Assuntos
Ascomicetos , Farmacorresistência Fúngica , Fungicidas Industriais , Arkansas , Ascomicetos/efeitos dos fármacos , Fungicidas Industriais/farmacologia , Concentração Inibidora 50 , Missouri , Estados Unidos
19.
Annu Rev Phytopathol ; 57: 253-277, 2019 08 25.
Artigo em Inglês | MEDLINE | ID: mdl-31206351

RESUMO

Quantitative resistance (QR) to crop diseases has usually been much more durable than major-gene, effector-triggered resistance. It has been observed that the effectiveness of some QR has eroded as pathogens adapt to it, especially when deployment is extensive and epidemics occur regularly, but it generally declines more slowly than effector-triggered resistance. Changes in aggressiveness and specificity of diverse pathogens on cultivars with QR have been recorded, along with experimental data on fitness costs of pathogen adaptation to QR, but there is little information about molecular mechanisms of adaptation. Some QR has correlated or antagonistic effects on multiple diseases. Longitudinal data on cultivars' disease ratings in trials over several years can be used to assess the significance of QR for durable resistance in crops. It is argued that published data likely underreport the durability of QR, owing to publication bias. The implications of research on QR for plant breeding are discussed.


Assuntos
Resistência à Doença , Doenças das Plantas , Adaptação Fisiológica , Produtos Agrícolas , Humanos
20.
Plant Dis ; 103(8): 1858-1864, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31242132

RESUMO

Although there has been research on managing Fusarium head blight (FHB) in spring barley, little has been published on cultivar resistance and optimal fungicide timing for FHB management in winter barley. A 3-year (2015 to 2017) field experiment was conducted to measure FHB resistance of winter barley varieties, gauge the potential benefit from a fungicide, and help determine the optimal timing for fungicide application. The split-plot experiment took place in a misted, inoculated nursery in Raleigh, North Carolina using main plots of four winter barley cultivars (Atlantic, Endeavor, Nomini, and Thoroughbred). Three fungicide treatments were applied to subplots: prothioconazole + tebuconazole at full spike emergence, the same fungicide 6 days later, or no fungicide. The late applications significantly reduced FHB index in each of 3 years and significantly reduced deoxynivalenol (DON) in harvested grain in 2 of the 3 years. Applications at full spike emergence also yielded significant benefit in 1 of the 3 years for each parameter. Neither disease symptoms nor DON gave reason to prefer one of the fungicide timings over the other. Across the 3 years, DON ranked the cultivars Endeavor < Nomini = Thoroughbred < Atlantic. Combining the moderate resistance of Endeavor with a fungicide application and averaging the two timings resulted in a 75% DON reduction compared with unsprayed Atlantic. Taken together, our results indicate that barley growers concerned about minimizing DON should both plant moderately resistant varieties and apply fungicide if there is scab risk. During the same period, 16 commercial winter barley cultivars were tested in from three to seven Virginia and North Carolina environments each, and the DON results were compared after standardization across environments. The winter two-row malting barley cultivars Endeavor and Calypso displayed superior and robust DON resistance across environments.


Assuntos
Resistência à Doença , Fungicidas Industriais , Fusarium , Hordeum , Resistência à Doença/genética , Fungicidas Industriais/farmacologia , Fusarium/efeitos dos fármacos , Fusarium/fisiologia , Hordeum/classificação , Hordeum/genética , Hordeum/microbiologia , North Carolina , Doenças das Plantas/microbiologia , Doenças das Plantas/prevenção & controle , Virginia
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