Emerson Medeiros Del Ponte

A New View of Sooty Blotch and Flyspeck

Sooty blotch and flyspeck (SBFS) fungi colonize the surface wax layer of the fruit of apple, pear, persimmon, banana, orange, papaya, and several other cultivated tree and vine crops. In addition to colonizing cultivated fruit crops, SBFS fungi also grow on the surfaces of stems, twigs, leaves, and fruit of a wide range of wild plants. The disease occurs worldwide in regions with moist growing seasons. SBFS is regarded as a serious disease by fruit growers and plant pathologists because it can cause substantial economic damage. The smudges and stipples of SBFS often result in downgrading of fruit from premium fresh-market grade to processing use. This review describes the major shifts that have occurred during the past decade in understanding the genetic diversity of the SBFS complex, clarifying its biogeography and environmental biology, and developing improved management strategies.

Regional and Field-Specific Factors Affect the Composition of Fusarium Head Blight Pathogens in Subtropical No-Till Wheat Agroecosystem of Brazil

A multiyear survey of >200 wheat fields in Paraná (PR) and Rio Grande do Sul (RS) states was conducted to assess the extent and distribution of Fusarium graminearum species complex (FGSC) diversity in the southern Brazilian wheat agroecosystem. Five species and three trichothecene genotypes were found among 671 FGSC isolates from Fusarium head blight (FHB)-infected wheat heads: F. graminearum (83%) of the 15-acetyldeoxynivalenol (15-ADON) genotype, F. meridionale (12.8%) and F. asiaticum (0.4%) of the nivalenol (NIV) genotype, and F. cortaderiae (2.5%) and F. austroamericanum (0.9%) with either the NIV or the 3-ADON genotype. Regional differences in FGSC composition were observed, with F. meridionale and the NIV type being significantly (P<0.001) more prevalent in PR (>28%) than in RS (≤9%). Within RS, F. graminearum was overrepresented in fields below 600 m in elevation and in fields with higher levels of FHB incidence (P<0.05). Species composition was not significantly influenced by previous crop or the stage of grain development at sampling. Habitat-specific differences in FGSC composition were evaluated in three fields by characterizing a total of 189 isolates collected from corn stubble, air above the wheat canopy, and symptomatic wheat kernels. Significant differences in FGSC composition were observed among these habitats (P<0.001). Most strikingly, F. meridionale and F. cortaderiae of the NIV genotype accounted for the vast majority (>96%) of isolates from corn stubble, whereas F. graminearum with the 15-ADON genotype was dominant (>84%) among isolates from diseased wheat kernels. Potential differences in pathogenic fitness on wheat were also suggested by a greenhouse competitiveness assay in which F. graminearum was recovered at much higher frequency (>90%) than F. meridionale from four wheat varieties inoculated with an equal mixture of F. graminearum and F. meridionale isolates. Taken together, the data presented here suggest that FGSC composition and, consequently, the trichothecene contamination in wheat grown in southern Brazil is influenced by host adaptation and pathogenic fitness. Evidence that F. meridionale and F. cortaderiae with the NIV genotype are regionally significant contributors to FHB may have significant implications for food safety and the economics of cereal production.

Inhibition of Fusarium graminearum growth and mycotoxin production by phenolic extract from Spirulina sp.

Fusarium graminearum is a fungal species complex pathogenic occurring worldwide, mainly associated with cereal crops. The most important Fusarium mycotoxins are fumonisins, zearalenone and trichothecenes. The availability of efficient control measures that are less harmful to both the environment and the consumers is urgent. For such, phenolic acids (PAs) from natural sources are known to reduce fungal contaminations. This work aimed to identify the PAs present in a culture extract of Spirulina algae (strain LEB-18) and evaluate its effect on mycelial growth rate, glucosamine level, amylase activity and mycotoxin production by four strains of two lineages of F. graminearum. Results showed that amendment of potato dextrose media with LEB-18 extract (3% w/v), which was mainly composed by gallic acid, greatly reduced radial growth of fungal colonies compared to media containing a single PA and the control. Also, average reductions of 40% and 62% in the glucosamine levels and the amylase activity were observed. In general, the LEB-18 extract and the PAs reduced mycotoxin concentration, with an average reduction of 68% for the trichothecene mycotoxins deoxynivalenol and nivalenol.

Phenotypic and pathogenic traits of two species of the Fusarium graminearum complex possessing either 15-ADON or NIV genotype

Fusarium head blight (FHB) in Brazil is caused mainly by two members of the Fusarium graminearum species complex, each possessing either a DON/15-ADON chemotype (F. graminearum sensu stricto, Fgss) or a NIV chemotype (F. meridionale, Fmer). In this work, we aimed to characterize and compare isolates belonging to each species, obtained either from wheat or barley, in relation to phenotypic traits (mycelial growth, sporulation and germination) and pathogenicity (in vitro glume infection and in vivo central floret inoculation) to two Brazilian wheat cultivars, Guamirim (moderate susceptible) and BRS 194 (susceptible). Results showed significantly higher growth rates, greater spore production and quicker germination for the Fgss isolates compared to the Fmer isolates, which were also more sensitivity to tebuconazole than the Fgss isolates. All isolates were capable of infecting glume tissues of both varieties, with an overall higher infection frequency for Fgss than Fmer isolates when inoculated in cv. Guamirim than in cv. BRS194, which showed similar infection frequency between the species. Accordingly, in the central-floret inoculation assay, Fgss isolates were also more aggressive than Fmer isolates towards cv. Guamirim, but not towards BRS194, based on the mean area under disease progress curves. It is hypothesized that phenotypic traits and host resistance may play a role in the selection of more aggressive populations under field conditions, thus partially explaining the dominance of Fgss populations associated with FHB of wheat in Brazil.

Triazole Sensitivity in a Contemporary Population of Fusarium graminearum from New York Wheat and Competitiveness of a Tebuconazole-Resistant Isolate

A sample of 50 isolates, including 25 each of the 3-acetyldeoxynivalenol and the 15-acetyldeoxynivalenol trichothecene genotype, from a contemporary collection of Fusarium graminearum associated with Fusarium head blight (FHB) of wheat in New York varied in sensitivity to tebuconazole (effective concentration leading to a 50% reduction of mycelial growth [EC50] of 0.28 to 8.09 mg/liter; μ = 1.12 mg/liter) and metconazole (0.05 to 0.86 mg/liter; μ = 0.33). Mean sensitivity did not differ between the trichothecene genotype groups. Isolate Gz448NY11 from Steuben County is the first tebuconazole-resistant field isolate of F. graminearum reported in the Americas and has the lowest sensitivity to tebuconazole (EC50 = 8.09 mg/liter) documented for this species. Suppression of FHB and deoxynivalenol (DON) following application of a commercial rate of tebuconazole was significantly diminished in plants inoculated with the tebuconazole-resistant isolate compared with those inoculated with a tebuconazole-sensitive isolate well documented for its aggressiveness and toxigenicity on wheat. There was no diminution of FHB and DON suppression with either isolate following application of metconazole. Significantly more individuals of the tebuconazole-resistant isolate were recovered from spikes inoculated with an equal mixture of the two isolates and sprayed with tebuconazole. Future studies are needed on the epidemiology and monitoring of triazole-resistant isolates to understand the risk that fungicide resistance poses to disease management and food security.

Improving sooty blotch and flyspeck severity estimation on apple fruit with the aid of standard area diagrams

Sooty blotch and flyspeck is caused by numerous species of fungi that colonize the surface of apple fruit and thereby lower its market value. Although this disease poses a substantial threat to apple growers’ profitability in some regions, reliable and cost-effective methods for epidemiological and disease control studies have not been validated, nor are they widely available. We modified a standard area diagram to aid sooty blotch and flyspeck severity assessments and quantified its impact on accuracy and precision of visual estimates. Samples of ‘Fuji’ and ‘Mutsu’ fruit were photographed both from the top and laterally. Severity was assessed from a sub-sample of 160 images using image analysis software. Validation of the diagram was performed by eight raters who independently assessed severity in two series of selected images representing the lateral view and the top view, initially unaided and subsequently with the aid of the scale. Severity estimates ranged from 0.4% to 98% (most fruit had <10% severity). Accuracy and precision of the estimates were significantly improved when using the diagrammatic scale; concordance correlation coefficient values increased from 0.81 to 0.95. A strong tendency to underestimate severity for the mid-range to high levels was minimized when using the aid, which also improved reproducibility of the estimates among raters. In addition to strengthening evidence that a standard area diagram can be used reliably in sooty blotch and flyspeck studies, we expanded its application to disease assessment in the peduncle region, which enhances the usefulness of the method for evaluating efficacy of management practices.

Meteorological factors and Asian soybean rust epidemics: a systems approach and implications for risk assessment

Condicoes meteorologicas e ambientais sao componentes criticos nas epidemias de ferrugem asiatica da soja (FAS), doenca causada pelo fungo Phakopsora pachyrhizi e que causa o maior dano na cultura da soja. Nesta revisao, o conhecimento sobre o efeito de fatores meteorologicos que influenciam nas epidemias foi usado para construir uma abordagem sistemica para compreender o risco de epidemias de FAS. Esta e baseada em uma estrutura hierarquica onde os fatores relevantes que afetam os estagios chave no ciclo da doenca foram delineados, incluindo os componentes aerobiologicos e epidemiologicos. As seguintes caracteristicas epidemiologicas foram avaliadas: liberacao de esporos, dispersao de esporos, deposicao de esporos, eficiencia de infeccao, periodo latente e producao de esporos. O conhecimento sobre os fatores meteorologicos que afetam cada um dos componentes foi revisado, sendo identificados os fatores mais importantes e as falhas de conhecimento, bem como as implicacoes para a previsao da doenca. A informacao e importante para orientar a pesquisa epidemiologica futura e especialmente desenvolver e melhorar modelos de risco da doenca em niveis locais a regionais.

Eficiência do controle da ferrugem asiática da soja em função do momento de aplicação sob condições de epidemia em Londrina, PR

Com o objetivo de estudar a eficiencia do controle da ferrugem asiatica da soja em funcao do momento de aplicacao foram conduzidos ensaios em Londrina, PR, Brasil, durante as safras 2005/06 e 2006/07. A mistura de 60 g azoxistrobina ha-1 + 24 g ciproconazol ha-1 foi aplicada em diferentes estadios fenologicos, iniciando em R2 ate R5.5, em aplicacoes unicas e sequenciais. A severidade foi estimada periodicamente para o calculo da area abaixo da curva de progresso da doenca (AACPD) e a produtividade avaliada no final do ciclo. Nas duas safras, os sintomas iniciais foram observados no final do estadio vegetativo. Na safra 2005/06, o tratamento com aplicacoes sequenciais, em R2 e R5.1, foi o mais eficiente na reducao da severidade e da AACPD e apresentou a maior produtividade. Na safra 2006/07, os tratamentos com aplicacoes sequenciais, em R2 e R5.1, e a aplicacao unica em R3 apresentaram as menores severidades, menores AACPD e maiores produtividades. Correlacoes negativas foram encontradas entre as variaveis severidade em R6 e AACPD e a produtividade (-0,83 e -0,84 em 2005/06 e -0,87 e -0,89 em 2006/07). As aplicacoes realizadas com niveis elevados de severidade, ao redor de 50%, apresentaram produtividade igual a testemunha nao tratada.

Models and applications for risk assessment and prediction of Asian soybean rust epidemics

Asian rust of soybean [Glycine max (L.) Merril] is one of the most important fungal diseases of this crop worldwide. The recent introduction of Phakopsora pachyrhizi Syd. & P. Syd in the Americas represents a major threat to soybean production in the main growing regions, and significant losses have already been reported. P. pachyrhizi is extremely aggressive under favorable weather conditions, causing rapid plant defoliation. Epidemiological studies, under both controlled and natural environmental conditions, have been done for several decades with the aim of elucidating factors that affect the disease cycle as a basis for disease modeling. The recent spread of Asian soybean rust to major production regions in the world has promoted new development, testing and application of mathematical models to assess the risk and predict the disease. These efforts have included the integration of new data, epidemiological knowledge, statistical methods, and advances in computer simulation to develop models and systems with different spatial and temporal scales, objectives and audience. In this review, we present a comprehensive discussion on the models and systems that have been tested to predict and assess the risk of Asian soybean rust. Limitations, uncertainties and challenges for modelers are also discussed.

Fitness Attributes of Fusarium graminearum Isolates from Wheat in New York Possessing a 3-ADON or 15-ADON Trichothecene Genotype

In all, 50 isolates of Fusarium graminearum from wheat spikes in New York, including 25 isolates each of the 15-acetyl-deoxynivalenol (15-ADON) and 3-ADON genotype, were tested to determine whether 3-ADON isolates are more fit for saprophytic survival and pathogenicity on wheat spikes than are 15-ADON isolates. The isolates were characterized and compared for 14 different attributes of saprophytic fitness and pathogenic fitness on a susceptible wheat variety. Isolates of the two genotypes could not be differentiated for most of these traits. Three principle components-ascospore production on corn stalks, total trichothecene amount in wheat kernels, and incidence of diseased spikelets up from the point of inoculation-accounted for 29.4, 18.9, and 10.8% of the variation among the isolates, respectively. A bootstrapping procedure grouped the isolates into two distinct groups, with 27 and 23 isolates each, with isolates from both genotypes represented in similar proportions (15-ADON/3-ADON, n = 14/13 and 11/12). Within the contemporary population of F. graminearum causing wheat head blight in New York, isolates with a 3-ADON genotype did not possess any detectable advantage over isolates with a 15-ADON genotype in saprophytic fitness or in pathogenic fitness on a susceptible wheat cultivar.