Weather-Based Logistic Regression Models for Predicting Wheat Head Blast Epidemics.

Wheat head blast is a major disease of wheat in the Brazilian Cerrado. Empirical models for predicting epidemics were developed using data from field trials conducted in Patos de Minas (2013 to 2019) and trials conducted across 10 other sites (2012 to 2020) in Brazil, resulting in 143 epidemics, with each being classified as either outbreak (≥20% head blast incidence) or nonoutbreak. Daily weather variables were collected from the National Aeronautics and Space Administration (NASA) Prediction of Worldwide Energy Resources (POWER) website and summarized for each epidemic. Wheat heading date (WHD) served to define four time windows, with each comprising two 7-day intervals (before and after WHD), which combined with weather-based variables resulted in 36 predictors (nine weather variables × four windows). Logistic regression models were fitted to binary data, with variable selection using least absolute shrinkage and selection operator (LASSO) and sequentially best subset analyses. The models were validated using the leave-one-out cross-validation (LOOCV) technique, and their statistical performance was compared. One model was selected, implemented in a 24-year series, and assessed by experts and literature. Models with two to five predictors showed accuracies between 0.80 and 0.85, sensitivities from 0.80 to 0.91, specificities from 0.72 to 0.86, and area under the curve (AUC) from 0.89 to 0.91. The accuracy of LOOCV ranged from 0.76 to 0.81. The model applied to a historical series included temperature and relative humidity in preheading date, as well as postheading precipitation. The model accurately predicted the occurrence of outbreaks, aligning closely with real-world observations, specifically tailored for locations with tropical and subtropical climates.

New Races with Wider Virulence Indicate Rapid Evolution of Puccinia striiformis f. sp. tritici in the Southern Cone of America.

Wheat yellow (stripe) rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases of wheat worldwide. Pst populations are composed of multiple genetic groups, each carrying one or more races characterized by different avirulence/virulence combinations. Since the severe epidemics in 2017, yellow rust has become the most economically important wheat foliar disease in Uruguay. A set of 124 Pst isolates collected from wheat fields in Uruguay between 2017 and 2021 were characterized phenotypically, and 27 of those isolates were subsequently investigated in-depth by additional molecular genotyping and race phenotyping analyses. Three genetic groups were identified, PstS7, PstS10, and PstS13, with the latter being the most prevalent. Two races previously reported in Europe, Warrior (PstS7) and Benchmark (PstS10), were detected in four and two isolates, respectively. A third race, known as Triticale2015 (PstS13), that was first detected in Europe in 2015 and in Argentina in 2017 was detected at several locations. Additional virulence to Yr3, Yr17, Yr25, Yr27, or Yr32 was detected in three new race variants within PstS13. The identification of these new races, which have not been reported outside South America, provides strong evidence of the local evolution of virulence in Pst during the recent epidemic years.

Genomic characterization of Puccinia triticina using molecular marker technology / Caracterização genômica de Puccinia triticina usando tecnologia de marcadores moleculares

Leaf rust, caused by Puccinia triticina, is the most common rust disease of wheat. The fungus is an obligate parasite capable of producing infectious urediniospores. To study the genetic structure of the leaf rust population 20 RAPD primers were evaluated on 15 isolates samples collected in Pakistan. A total of 105 RAPD fragments were amplified with an average of 7 fragments per primer. The number of amplified fragments varied from 1 to 12. GL Decamer L-07 and GL Decamer L-01 amplified the highest number of bands (twelve) and primer GL Decamer A-03 amplified the lowest number of bands i.e one. Results showed that almost all investigated isolates were genetically different that confirms high genetic diversity within the leaf rust population. Rust spores can follow the migration pattern in short and long distances to neighbor areas. Results indicated that the greatest variability was revealed by 74.9% of genetic differentiation within leaf rust populations. These results suggested that each population was not completely identical and high gene flow has occurred among the leaf rust population of different areas. The highest differentiation and genetic distance among the Pakistani leaf rust populations were detected between the leaf rust population in NARC isolate (NARC-4) and AARI-11and the highest similarity was observed between NARC isolates (NARC-4) and (NARC-5). The present study showed the leaf rust population in Pakistan is highly dynamic and variable.

A ferrugem da folha, causada por Puccinia triticina, é a ferrugem mais comum do trigo. O fungo é um parasita obrigatório, capaz de produzir urediniósporos infecciosos. Para estudar a estrutura genética da população de ferrugem da folha, 20 primers RAPD foram avaliados em 15 amostras de isolados coletadas no Paquistão. Um total de 105 fragmentos RAPD foram amplificados com uma média de 7 fragmentos por primer. O número de fragmentos amplificados variou de 1 a 12. GL Decamer L-07 e GL Decamer L-01 amplificaram o maior número de bandas (doze), e o primer GL Decamer A-03 amplificou o menor número de bandas, ou seja, um. Os resultados mostraram que quase todos os isolados investigados eram geneticamente diferentes, o que confirma a alta diversidade genética na população de ferrugem da folha. Os esporos de ferrugem podem seguir o padrão de migração em distâncias curtas e longas para áreas vizinhas. Os resultados indicaram que a maior variabilidade foi revelada por 74,9% da diferenciação genética nas populações de ferrugem. Esses resultados sugeriram que cada população não era completamente idêntica e um alto fluxo gênico ocorreu entre a população de ferrugem da folha de diferentes áreas. A maior diferenciação e distância genética entre as populações de ferrugem da folha do Paquistão foram detectadas entre a população de ferrugem da folha no isolado NARC (NARC-4) e AARI-11 e a maior similaridade foi observada entre os isolados NARC (NARC-4) e (NARC-5). O presente estudo mostrou que a população de ferrugem da folha no Paquistão é altamente dinâmica e variável.

Mapping of leaf rust resistance genes in common wheat 'Guinong08-6' / Mapa de genes de resistência à ferrugem da folha em trigo 'Guinong08-6'

Wheat leaf rust (Puccinia triticina Eriks.), a devastating disease of wheat in the world, causes severe yield losses and therefore the development of resistant cultivars is very important. Here, a Chinese wheat line (Guinong08-6) showed adult-plant resistance against mixed fungal isolates of leaf rust, which is common in Guiyang region. It was crossed with a susceptible wheat line (Guinong19) to develop F1, F2, and F3 hybrids. Combined SSR and STS markers were used to map leaf rust resistance genes in Guinong08-6, and the resistance phenotype of Guinong08-6 was co-regulated by two complementary dominant genes, named LrGn08-6A and LrGn08-6B. LrGn08-6A was mapped to chromosome 2AS with markers URIC-LN2 and Xgpw2204, which flanked the gene at distances of 1.8 centimorgan (cM) and 14.83 cM, respectively. LrGn08-6B was mapped to chromosome 4DL with markers Xgpw342 and Xbarc93, which both flanked the gene at a distance of 26.57 cM. Genetic and molecular marker analyses demonstrated that LrGn08-6A, which was inherited from Aegilops ventricosa may be the resistance gene Lr37, while LrGn08-6B may be a newly discovered leaf rust resistance gene.(AU)

A ferrugem da folha do trigo (Puccinia triticina Eriks.), importante doença do trigo em todo o mundo, causa graves perdas de rendimento e, portanto, o desenvolvimento de cultivares resistentes é muito importante. Nesta pesquisa, uma linhagem chinesa de trigo (Guinong08-6) mostrou resistência de plantas adultas a uma mistura de isolados do patógeno, na região de Guiyang, China. Essa linhagem foi cruzada com uma linhagem suscetível de trigo (Guinong19) para desenvolver híbridos F1, F2 e F3. Combinados de marcadores SSR e STS foram usados para mapear genes de resistência à ferrugem da folha em Guinong08-6, e o fenótipo de resistência de Guinong08-6 foi co-regulado por dois genes dominantes complementares, chamados LrGn08-6A e LrGn08-6B. LrGn08-6A foi mapeado para o cromossomo 2AS com marcadores URIC-LN2 e Xgpw2204, que flanquearam o gene em distâncias de 1,8 centimorgano (cM) e 14,83 cM, respectivamente. LrGn08-6B foi mapeado para o cromossomo 4DL com marcadores Xgpw342 e Xbarc93, e ambos flanquearam o gene a uma distância de 26,57 cM. As análises genéticas e moleculares de marcadores demonstraram que LrGn08-6A, que foi herdado de Aegilops ventricosa, pode ser o gene de resistência Lr37, enquanto LrGn08-6B pode ser um gene recentemente descoberto de resistência à ferrugem da folha do trigo.(AU)

Genomic characterization of Puccinia triticina using molecular marker technology.

Leaf rust, caused by Puccinia triticina, is the most common rust disease of wheat. The fungus is an obligate parasite capable of producing infectious urediniospores. To study the genetic structure of the leaf rust population 20 RAPD primers were evaluated on 15 isolates samples collected in Pakistan. A total of 105 RAPD fragments were amplified with an average of 7 fragments per primer. The number of amplified fragments varied from 1 to 12. GL Decamer L-07 and GL Decamer L-01 amplified the highest number of bands (twelve) and primer GL Decamer A-03 amplified the lowest number of bands i.e one. Results showed that almost all investigated isolates were genetically different that confirms high genetic diversity within the leaf rust population. Rust spores can follow the migration pattern in short and long distances to neighbor areas. Results indicated that the greatest variability was revealed by 74.9% of genetic differentiation within leaf rust populations. These results suggested that each population was not completely identical and high gene flow has occurred among the leaf rust population of different areas. The highest differentiation and genetic distance among the Pakistani leaf rust populations were detected between the leaf rust population in NARC isolate (NARC-4) and AARI-11and the highest similarity was observed between NARC isolates (NARC-4) and (NARC-5). The present study showed the leaf rust population in Pakistan is highly dynamic and variable.

Molecular Characterization of Wheat Stripe Rust Pathogen (Puccinia striiformis f. sp. tritici) Collections from Nine Countries.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases of wheat worldwide. To understand the worldwide distribution of its molecular groups, as well as the diversity, differentiation, and migration of the Pst populations, 567 isolates collected from nine countries (China, Pakistan, Italy, Egypt, Ethiopia, Canada, Mexico, Ecuador, and the U.S.) in 2010-2018 were genotyped using 14 codominant simple sequence repeat markers. A total of 433, including 333 new multi-locus genotypes (MLGs), were identified, which were clustered into ten molecular groups (MGs). The MGs and country-wise populations differed in genetic diversity, heterozygosity, and correlation coefficient between the marker and virulence data. Many isolates from different countries, especially the isolates from Mexico, Ecuador, and the U.S., were found to be identical or closely related MLGs, and some of the MGs were present in all countries, indicating Pst migrations among different countries. The analysis of molecular variance revealed 78% variation among isolates, 12% variation among countries, and 10% variation within countries. Only low levels of differentiation were found by the pairwise comparisons of country populations. Of the 10 MGs, 5 were found to be involved in sexual and/or somatic recombination. Identical and closely related MLGs identified from different countries indicated international migrations. The study provides information on the distributions of various Pst genetic groups in different countries and evidence for the global migrations, which should be useful in understanding the pathogen evolution and in stressing the need for continual monitoring of the disease and pathogen populations at the global scale.

High frequency of fungicide resistance-associated mutations in the wheat yellow rust pathogen Puccinia striiformis f. sp. tritici.

BACKGROUND: Reliance on fungicides to manage disease creates selection pressure for the evolution of resistance in fungal and oomycete pathogens. Rust fungi (Pucciniales) are major pathogens of cereals and other crops and have been classified as low-risk for developing resistance to fungicides; no case of field failure of fungicides in a cereal rust disease has yet been recorded. Recently, the Asian soybean rust pathogen, Phakopsora pachyrhizi evolved resistance to several fungicide classes, prompting us to screen a large sample of the globally widespread wheat yellow rust pathogen, Puccinia striiformis f. sp. tritici (Pst), for mutations associated with fungicide resistance. RESULTS: We evaluated 363 Pst isolates from Europe, the USA, Ethiopia, Chile, China and New Zealand for mutations in the target genes of demethylase inhibitor (DMI; Cyp51) and succinate dehydrogenase inhibitor (SDHI; SdhB, SdhC and SdhD) fungicides. A high proportion of Pst isolates carrying a Y134F DMI resistance-associated substitution in the Cyp51 gene was found among those from China and New Zealand. A set of geographically diverse Pst isolates was also found to display a substitution in SdhC (I85V) that is homologous to that reported recently in P. pachyrhizi and linked to SDHI resistance. CONCLUSION: The identification of resistance-associated alleles confirms that cereal rusts are not immune to fungicide resistance and that selection for resistance evolution is operating at high levels in certain locations. It highlights the need to adopt fungicide resistance management practices and to monitor cereal rust species for development of resistance. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Genome-wide mapping and allelic fingerprinting provide insights into the genetics of resistance to wheat stripe rust in India, Kenya and Mexico.

Stripe or yellow rust (YR) caused by Puccinia striiformis Westend. f. sp. tritici Erikss. is a persistent biotic-stress threatening global wheat production. To broaden our understanding of the shared genetic basis of YR resistance across multi-site and multi-year evaluations, we performed a large genome-wide association study using 43,706 YR observations on 23,346 wheat lines from the International Maize and Wheat Improvement Center evaluated between 2013 and 2019 at sites in India, Kenya and Mexico, against predominant races prevalent in the countries. We identified 114 repeatable markers tagging 20 quantitative trait loci (QTL) associated with YR on ten chromosomes including 1D, 2A, 2B, 2D, 3A, 4A, 4D, 5A, 5B and 6B, among which four QTL, QYr.cim-2DL.2, QYr.cim-2AS.1, QYr.cim-2BS.2 and QYr.cim-2BS.3 were significant in more than ten datasets. Furthermore, we report YR-associated allelic fingerprints for the largest panel of wheat breeding lines (52,067 lines) till date, creating substantial opportunities for YR favorable allele enrichment using molecular markers. Overall, the markers and fingerprints reported in this study provide excellent insights into the genetic architecture of YR resistance in different geographical regions, time-periods and wheat germplasm and are a huge resource to the global wheat breeding community for accelerating YR resistance breeding efforts.

Alteraciones histopatológicas causadas por la roya Puccinia nakanishikii (Pucciniales: Pucciniaceae) en plantas de Cymbopogon citratus (Poaceae) / Histopathological alterations caused by Puccinia nakanishikii rust (Pucciniales: Pucciniaceae) in Cymbopogon citratus (Poaceae) plants

Introducción: Los aspectos histopatológicos e histoquímicos relacionados con el ataque de royas en plantas, así como su relación con los diferentes estados espóricos, son escasos en la literatura científica. Objetivos: Describir y analizar los aspectos histopatológicos e histoquímicos en Cymbopogon citratus y su relación con los diferentes estados espóricos de la roya Puccinia nakanishikii. Métodos: Durante abril y agosto 2013 se recolectaron hojas sanas e infectadas con Puccinia nakanishikii en la escarpa noroccidental de la meseta de Bucaramanga-Colombia. Las muestras con lesiones en diferentes etapas del desarrollo se fijaron y procesaron de acuerdo a protocolos estándar para la inclusión y corte en parafina y resina. Las secciones obtenidas en parafina (5-7 µm) fueron teñidas con Safranina-azul de Alcian y azul de Alcian-Hematoxilina. En tanto que las secciones obtenidas en resina (0.5 µm) se tiñeron con azul de Toluidina. También se elaboraron secciones a mano alzada para análisis de autofluorescencia. Las observaciones y registro fotográfico se efectuaron con microscopio fotónico y microscopía de epifluorescencia. Para observaciones con microscopía electrónica de barrido (MEB), las muestras se fijaron en Glutaraldehído, se deshidrataron con 2,2 dimetoxipropano, se desecaron a punto crítico y se metalizaron con oro. Resultados: Las hojas son por lo general hipostomáticas, con células epidérmicas largas y cortas formando filas paralelas y con la presencia de tricomas unicelulares espinosos y microtricomas. La superficie abaxial está cubierta por una densa capa de ceras epicuticulares y la adaxial está formada por agrupaciones de células buliformes y células epidérmicas de contorno rectangular o cuadrado. En el mesófilo no hay diferenciación entre parénquima de empalizada y esponjoso y su anatomía refleja el metabolismo C4 presente en esta gramínea. Se observó la formación de urediosoros y teliosoros hipófilos. Las urediosporas son la fase de reinfección y estas tienen de 4-5 poros germinativos ecuatoriales y su pared es equinulada. Las teliosporas son de pared lisa y de pedicelo persistente. Las urediosporas forman tubos de geminación por lo general sobre la superficie abaxial de la hoja y se desarrollan en dirección de los estomas, por donde penetran al interior del mesófilo. No se observó la presencia de apresorios. La epidermis se desprende y levanta por del desarrollo de las urediosporas y las paráfisis capitadas, a medida que el urediosoro crece. Con el avance de la infección, los tejidos fotosintéticos se desorganizan, pierden la autofluorescencia de la clorofila y las células sufren necrosis. Posteriormente, los tejidos vasculares se fragmentan y colapsan. Para este momento, la infección se ha extendido sobre toda la lámina foliar llevando a la muerte de la hoja y defoliación de la planta. Durante etapas avanzadas de la infección en los urediosoros se observaron picnidios, probablemente del hiperparásito Sphaerellopsis, asociados estrechamente a los tejidos infectados por la roya. Conclusiones: Puccinia nakanishikii se desarrolla sobre las hojas de Cymbopogon citratus produciendo urediosoros y teliosoros. Las urediosporas son la fase de reinfección, y las teliosporas solo se observaron en etapas avanzadas de la infección. La epidermis y los tejidos fotosintéticos son severamente afectados por la necrosis celular. En etapas avanzadas de la infección los tejidos vasculares se ven afectados.

Introduction: Histopathological and histochemical aspects linked to the attack of fungal rusts to plants, as well as its relation with the different spore stages are topics rather scarce in the scientific literature. Objective: To describe and analyze the histopathological and histochemical aspects of Cymbopogon citratus and its relation with the different stages of the spores from the rust fungi Puccinia nakanishikii. Methods: During the months April and August 2013, leaves healthy and infected by Puccinia nakanishikii were collected in the Northwestern scarp of the Bucaramanga-Colombia plateau. The samples with injuries on diverse developmental stages were fixated and processed according to the standard protocols for embedding and sectioning in paraffin and resin. Sections obtained from paraffin (5-7 µm) were stained with Safranin-Alcian blue and Alcian blue-Hematoxylin. On the other hand, sections obtained from resin (0.5 µm) were stained with Toluidine blue. Further, freehand sections were obtained for an autofluorescence analysis. The observations and photographic record were done via photonic microscope and epifluorescence microscope. For the observations via scanning electron microscopy (SEM), the samples were fixated in Glutaraldehyde, dehydrated with 2,2 dimethoxypropane, then desiccated to critical point and finally coated with gold. Results: The leaves are generally hypostomatic, with long and short epidermic cell forming parallel rows and showing unicellular prickle trichomes and micro-trichomes. The abaxial surface is covered by epicuticular wax forming a dense layer. The adaxial epidermis is formed by groupings of bulliform cells and epidermal cells with rectangular or squared contour. In the mesophyll, there is no differentiation between palisade and spongy parenchyma, its anatomy reflects the C4 metabolism. The formation of uredosori and teliosori both hypophyllous was observed. Urediniospores are the reinfecting agents phase, they have 4-5 equatorial germ pores and echinulate wall. Teliospores have smooth wall and a persistent pedicel. The urediniospores form a germ tube, generally on the abaxial leaf surface, these tubes develop towards the stomata reaching the mesophyll interior. No appressorium were observed. The epidermis limiting the uredosorus detaches due the development and pressure that exert both the urediniospores and capitate paraphyses. As the infection progresses, autofluorescense of the chlorophyll is lost and the cells undergo necrotic processes. Afterwards, the phloem collapses and the xylem becomes slightly disorganized. At this moment, the infection is extended along the whole leaf blade, resulting in the leaf death and the plant defoliation. On advanced stages of the infection, the uredosori showed pycnidia, probably belonging to the hyperparasite Sphaerellopsis, these structures were closely associated to the rust infected tissues. Conclusions: Puccinia nakanishikii develops on the leaves of Cymbopogon citratus producing uredosori and teliosori. Urediniospores are the reinfective stage, teliospores were only observed at late stages of the infection. The epidermis and photosynthetic tissue are severely affected by cell necrosis. The vascular tissues are deeply affected on the advances stages of the infection.

Time-series expression profiling of sugarcane leaves infected with Puccinia kuehnii reveals an ineffective defense system leading to susceptibility.

KEY MESSAGE: Successful orange rust development on sugarcane can potentially be explained as suppression of the plant immune system by the pathogen or delayed plant signaling to trigger defense responses. Puccinia kuehnii is an obligate biotrophic fungus that infects sugarcane leaves causing a disease called orange rust. It spread out to other countries resulting in reduction of crop yield since its first outbreak. One of the knowledge gaps of that pathosystem is to understand the molecular mechanisms altered in susceptible plants by this biotic stress. Here, we investigated the changes in temporal expression of transcripts in pathways associated with the immune system. To achieve this purpose, we used RNA-Seq to analyze infected leaf samples collected at five time points after inoculation. Differential expression analyses of adjacent time points revealed substantial changes at 12, 48 h after inoculation and 12 days after inoculation, coinciding with the events of spore germination, haustoria post-penetration and post-sporulation, respectively. During the first 24 h, a lack of transcripts involved with resistance mechanisms was revealed by underrepresentation of hypersensitive and defense response related genes. However, two days after inoculation, upregulation of genes involved with immune response regulation provided evidence of some potential defense response. Events related to biotic stress responses were predominantly downregulated in the initial time points, but expression was later restored to basal levels. Genes involved in carbohydrate metabolism showed evidence of repression followed by upregulation, possibly to ensure the pathogen nutritional requirements were met. Our results support the hypothesis that P. kuehnii initially suppressed sugarcane genes involved in plant defense systems. Late overexpression of specific regulatory pathways also suggests the possibility of an inefficient recognition system by a susceptible sugarcane genotype.

Endemic and panglobal genetic groups, and divergence of host-associated forms in worldwide collections of the wheat leaf rust fungus Puccinia triticina as determined by genotyping by sequencing.

The wheat leaf rust fungus, Puccinia triticina, is found in the major wheat growing regions of the world and is a leading cause of yield loss in wheat. Populations of P. triticina are highly variable for virulence to resistance genes in wheat and adapt quickly to resistance genes in wheat cultivars. The objectives of this study were to determine the genetic relatedness of worldwide collections of P. triticina using restriction site associated genotyping by sequencing. A total of 558 isolates of P. triticina from wheat producing regions in North America, South America, Europe, the Middle East, Ethiopia, Russia, Pakistan, Central Asia, China, New Zealand, and South Africa were characterized at 6745 single nucleotide loci. Isolates were also tested for virulence to 20 near-isogenic lines that differ for leaf rust resistance genes. Populations that were geographically proximal were also more closely related for genotypes. In addition, groups of isolates within regions that varied for genotype were similar to groups from other regions, which indicated past and recent migration across regions. Isolates from tetraploid durum wheat in five different regions were highly related with distinct genotypes compared to isolates from hexaploid common wheat. Based on a molecular clock, isolates from durum wheat found only in Ethiopia were the first to diverge from a common ancestor form of P. triticina that is found on the wild wheat relative Aegilops speltoides, followed by the divergence of isolates found worldwide that are virulent to durum wheat, and then by isolates found on common wheat.

Controle da ferrugem da folha do trigo (Puccinia triticina) em diferentes momentos de aplicação de fungicida / Control of wheat leaf rust (Puccinia triticina) at different timings of fungicide application

A aplicação de fungicidas tem importante papel na cultura do trigo e sua eficácia está atrelada principalmente ao momento biológico para o controle. O objetivo deste trabalho foi estudar a influência do momento de aplicação de fungicida nos danos decorrentes da ferrugem da folha do trigo (P. triticina). Um coletor de esporos Siga foi instalado na área experimental a fim de auxiliar na previsão da ocorrência da ferrugem antes da manifestação dos sintomas. O cultivar utilizado foi o CD 104 ­ susceptível à ferrugem ­ e as aplicações foram realizadas aos 7, 14 e 21 dias após a manifestação dos primeiros sintomas de ferrugem nas plantas. Avaliaram-se neste experimento a área abaixo da curva de progresso da doença, obtida pela sua severidade, e os índices de produtividade (kg/ha) e peso hectolitro (g) da cultura. O coletor Siga foi capaz de detectar esporos de ferrugem antes da manifestação sintomática da doença, auxiliando na sua identificação no campo nos primeiros sintomas. O atraso nas aplicações de fungicida aumentou os níveis de severidade, reduzindo significativamente o nível de controle e ocasionando danos consideráveis à produtividade da cultura. Verificaram-se perdas de produtividade na ordem de 80 kg por dia de atraso na aplicação.

The fungicide application is important to the wheat field and its efficacy is related mainly to the biologic timing for the control. The aim of this paper was to study the influence of timing of fungicide application in the damage caused by leaf rust of wheat (P. triticina). A spore trap Siga was installed in the experimental area to assist the prediction of leaf rust before the first symptom. The cultivar used was CD 104 ­ susceptible to the rust ­ and the applications were made at 7, 14 and 21 days after the first symptoms of the leaf rust on the plants. It was evaluated in this experiment the area under the disease progress curve, obtained by the disease severity, and the yield (kg/ha) and hectolitre weight (g) indexes of the field. The trap Siga was able to detect spores of leaf rust before the disease symptoms, supporting its identification in the field in the first symptoms. The delay of the fungicide application increased the level of disease severity, reducing significantly the control level and causing considerable damage to the crop yield. It was verified yield losses approximately of 80 kg per day of delay of the application.