Tropical Plant Pathology, Volume: 37, Issue: 4, Published: 2012
  • Activity of extracellular compounds of Pseudomonas sp. against Xanthomonas axonopodis in vitro and bacterial leaf blight in eucalyptus Articles

    Lopes, Lucilene P.; Oliveira Jr, Admiltom G.; Beranger, Jamile P.O.; Góis, Cíntia G.; Vasconcellos, Fernanda C.S.; Martin, Juca A.B. San; Andrade, Célia G.T.J.; Mello, João C.P.; Andrade, Galdino

    Abstract in English:

    Bacterial leaf blight caused by Xanthomonas axonopodis is a major problem in the production of eucalyptus seedlings. The pathogen causes leaf lesions that reduce the photosynthetic area and limit plant growth. The objective of this study was to evaluate the antibiotic activity of secondary metabolic compounds of a Pseudomonas sp. against X. axonopodis, following extraction with dichloromethane and fractionation by vacuum liquid chromatography. The antibiotic activity of an ethyl acetate phase (F3 fraction) was determined by agar diffusion tests and bioautography. The minimum inhibitory concentration of F3 fraction and the action of F3 on the cell morphology of X. axonopodis was determined by scanning electron microscopy. Electron microscopy revealed changes in exopolysaccharides and morphology of treated cells. When eucalyptus seedlings were sprayed with the F3 fraction before or after inoculation with X. axonopodis in a greenhouse experiment the number of leaf lesions was respectively 93.9% and 89.7% lower than in untreated control plants. High antibiotic activity of the F3 fraction against X. axonopodis and leaf blight suggests that it has potential to control the disease in eucalyptus seedlings.
  • Determination of optimal conditions for Spongospora subterranea zoospore release on bioassays

    Puerta, Carolina Corrales; Amaya, Catalina Zuluaga; Torres, José Miguel Cotes; González-Jaimes, Elena Paola

    Abstract in Spanish:

    La sarna polvosa de la papa es causada por Spongospora subterranea f. sp. subterranea, parasito obligado y patógeno del suelo, que afecta el sistema radicular y tubérculos de papa. Igualmente es vector del pomovirus Potato mop-top virus (PMTV). Este organismo posee quistosoros como estructuras de resistencia las cuales le confieren la posibilidad de permanecer en el suelo por años. Este estudio busca determinar bajo que condiciones de temperatura, fuentes de inóculo y sustratos se obtiene una máxima liberación de zoosporas con el fin de utilizar esta metodología en pruebas de infección de S. subterranea. Así se realizaron tres ensayos donde se evaluaron tres fuentes de inóculo (suelo, raíz, tubérculo), tres medios líquidos (agua, extracto de raíz y solución nutritiva) y diferentes temperaturas. Las observaciones fueron realizadas en microscopio con cámara de Neubauer por conteo de zoosporas móviles, con lecturas en el tiempo a partir de las 24 hasta las 120 horas. Se encontró como resultado diferencias significativas en los sustratos empleados para liberación manifestándose mayor liberación de zoosporas en extracto de raíz en temperatura fluctuante de 20-15°C a partir de las 24 horas de inoculación hasta las 96 horas.

    Abstract in English:

    Potato powdery scab is caused by Spongospora subterranea f. sp. subterranea, an obligate parasite and soil-borne pathogen which affects the root system and tubers. It is also a vector of the pomovirus Potato mop-top virus (PMTV). This organism has resistance structures called cystosori which allows it to remain in the soil for years. This study aimed to determine the optimal conditions of temperature, inoculum sources and substrate for zoospore release, for future use in infectivity assays. Three experiments were conducted in which three inoculum sources (soil, roots and tubers), three liquid substrates (water, root extract and nutrient solution) and different temperatures were tested. Observations of mobile zoospores were made in a light microscope equipped with a Neubauer chamber, from 24 until 120 hours after inoculation. Significant differences were found among the different treatments, with the optimal conditions using root extract as inoculum source, temperature between 15 and 20°C, from 24 until 96 hours after inoculation.
  • Technical and economic feasibility of strobilurin fungicides application on maize Artigos

    Costa, Rodrigo Véras da; Cota, Luciano Viana; Silva, Dagma Dionísia da; Meirelles, Walter Fernandes; Lanza, Fabrício Eustáquio

    Abstract in Portuguese:

    Nos últimos anos, grande ênfase tem sido dada ao uso de fungicidas para o manejo de doenças foliares na cultura do milho no Brasil. Esse trabalho teve como objetivo a realização de uma análise da viabilidade técnica e econômica da aplicação de fungicidas no rendimento de cultivares de milho em diferentes regiões produtoras. Foram conduzidos experimentos para avaliação do efeito da aplicação de fungicidas no rendimento de diferentes cultivares de milho, em três localidades: Sete Lagoas (MG), Londrina (PR) e Rio Verde (GO). Foram consideradas a não aplicação, uma e duas aplicações de fungicidas em cada cultivar. Foram avaliadas a severidade das doenças foliares e o rendimento de cada cultivar. Os resultados de rendimento das cultivares tratadas com fungicidas apresentaram elevada inconsistência em condições de baixa severidade de doenças. Maior frequência de rendimentos positivos e benefício econômico ocorreu quando as aplicações de fungicida foram realizadas em condição de elevada pressão de doença. Mais estudos são necessários para o melhor entendimento do efeito dos fungicidas do grupo das estrobilurinas na fisiologia e na produção de plantas de milho.

    Abstract in English:

    In recent years, great emphasis has been given to the use of fungicides for managing foliar diseases in corn in Brazil. This study aimed to conduct an analysis of technical and economic feasibility of application of fungicides on maize in different growing regions. Trials were conducted to evaluate the effect of fungicides on the yield of different maize cultivars at three locations: Sete Lagoas (state of Minas Gerais), Londrina (state of Paraná) and Rio Verde (state of Goiás). The effect of one and two fungicide applications on each cultivar was evaluated. For each trial, the difference in mean yield and disease severities between treated and untreated plots for each cultivars was compared. For all trials, yield response of cultivars treated with fungicides was highly inconsistent under low disease severity. A higher frequency of positive yields and economic benefit occurred when fungicide applications were made under conditions of high disease pressure. More studies are needed to better clarify the effect of strobilurin fungicides on the physiology and production of corn plants.
  • Yield loss caused by rust in soybean cultivars sown in different periods in the western region of Bahia, Brazil Artigos

    Cruz, Thyane V. da; Peixoto, Clovis P.; Martins, Mônica C.; Laranjeira, Francisco F.; Lopes, Pedro V. Lima; Andrade, Newton S.; Ledo, Carlos A. da Silva

    Abstract in Portuguese:

    Este trabalho teve como objetivo quantificar os danos causados pela ferrugem-asiática em três cultivares de soja, semeadas em diferentes épocas, na região Oeste da Bahia. Os experimentos foram instalados no município de São Desidério, BA, nas safras 2007/2008 e 2008/2009. O delineamento experimental foi em blocos casualizados com quatro repetições, no esquema de parcelas subdivididas no espaço. A parcela foi representada pelos tratamentos de controle da ferrugem (com ou sem aplicação de fungicida) e as subparcelas foram representadas pelas cultivares (Monsoy 8411, BRS Corisco e BRS Barreiras). Avaliou-se a severidade da ferrugem para o cálculo da área abaixo da curva de progresso da doença padronizada (AACPDp), o número de folhas ao longo do ciclo e a produtividade de grãos. O modelo logístico foi o que melhor se ajustou aos dados da severidade. A variação temporal do número de folhas foi ajustada pela função polinomial exponencial Ln (y) = a + bx1,5 + cx0,5. As médias da AACPDp e a da produtividade foram comparadas pelo teste de Tukey a 5% de probabilidade. Os danos causados pela ferrugem-asiática da soja na região foram potencializados na época de semeadura tardia, ocorrendo desfolha antecipada e redução na produtividade de grãos.

    Abstract in English:

    The objective of this work was to quantify the yield loss caused by Asian soybean rust in three cultivars sown in different periods in the western region of Bahia. The experiments were installed in São Desidério, BA, in the growing seasons 2007/2008 and 2008/2009. The experimental design was carried out in random blocks with four replicates and subdivided plot scheme in time. The plot was represented by the rust control treatments (with and without chemical control) and the subplots represented by cultivars (Monsoy 8411, BRS Corisco and BRS Barreiras). The severity, number of leaves throughout the cycle and yield were evaluated. The logistic model was the one that better fitted the severity data whereas the polynominal exponential function Ln (y) = a + bx1, 5 + cx0,5 fitted the temporal variation of number of leaves better. The means of the area under the disease progress curve and yield were compared by Tukey test. Yield loss increased during later sowing periods due to greater inoculum pressure hindering disease control and decreasing grain yield.
  • Comparison of two methods for in vitro multiplication of Radopholus similis and Pratylenchus brachyurus in carrot cylinders Short Communications

    Santos, Jansen R.P.; Andrade, Ednalva P.; Costa, Dilson C.; Gonzaga, Vilmar; Cares, Juvenil E.

    Abstract in English:

    The use of in vitro mass multiplication of nematodes under axenic conditions allows intensification of studies on taxonomy, biology, epidemiology and control of these pathogens. In the present study, two methods were compared for in vitro multiplication of two species of plant-parasitic nematodes, Radopholus similis and Pratylenchus brachyurus in 20, 40 and 60 day-periods. Both techniques involved the use of carrot cylinders placed in jars with lids, with water-agar in the bottom of the flasks (WA+) or without (WA-). In WA- the nematodes were treated with a 1% solution of ampicillin whilst for WA+ the axenization was carried out with a solution of mercuric chloride (0.01%), and streptomycin sulfate 0.02%. The WA+ condition was the most favorable for multiplication of both species of nematodes, resulting in a population increase of about 280 times for R. similis and 226 times for P. brachyurus in relation to the founding population of 25 individuals. For WA- a population increase of only five times after 60 days for R. similis and a duplication of the population after 60 days for P. brachyurus was obtained. Overall, the largest amount of nematodes occurred at 60 days after inoculation.
  • Survival of Diaporthe phaseolorum var. caulivora (causal agent of soybean stem canker) artificially inoculated in different crop residues Short Communications

    Grijalba, Pablo; Ridao, Azucena del C.

    Abstract in English:

    Stem canker caused by Diaporthe phaseolorum var. caulivora is an important disease of soybean in Argentina. The objective of this study was to determine its survival ability in artificially infested straw under laboratory and field conditions. In laboratory, stem pieces of soybean, maize, sorghum, sunflower, potato and wheat were autoclaved, placed in petri dishes on Potato Dextrose Agar and Water Agar, and inoculated with a 7-day-old pathogen culture. All crop residues were colonized and produced perithecia. Debris artificially infested with D. phaseolorum var. caulivora were placed in plastic net bags and transferred to an un-cropped area in a field plot at the University of Buenos Aires. Straws were left on the ground from winter to spring season in both 2007 and 2008 years. After 6 months abundant perithecia were developed in all straws. However, a higher number of perithecia on soybean and sunflower compared to maize, sorghum and potato was determined. These findings suggest that other crops, besides soybean, could maintain alive the inoculum of Diaporthe phaseolorum var. caulivora from soybean for at least 6-7 months.
  • Local protection, not systemic, of potassium silicate to decrease coffee leaf rust symptoms Comunicações

    Carré-Missio, Vivian; Rodrigues, Fabrício Ávila; Schurt, Daniel Augusto; Moreira, Wiler Ribas; Rezende, Dalilla Carvalho; Korndörfer, Gaspar Henrique; Zambolim, Laércio

    Abstract in Portuguese:

    No primeiro experimento, plantas de cafeeiro com três pares de folhas foram pulverizadas com silicato de potássio (K2SiO3), epoxiconazole, acibenzolar-S-metil (ASM) e água destilada de duas maneiras: pulverização do 3º par de folhas, a partir do ápice, protegendo o 2º par de folhas ou pulverização de um par de folhas da lateral esquerda da planta e protegendo o par de folhas da lateral direita. Após 24 h, a face abaxial dos pares de folhas protegidos foi inoculada com Hemileia vastatrix. No segundo experimento, o 3º par de folhas de plantas, a partir do ápice, foi pulverizado com K2SiO3, ASM e água destilada protegendo o 2º par de folhas. Aos 1, 5, 15, 25 e 35 dias após aplicação dos produtos, a face abaxial do 2º (proteção sistêmica) e do 3º par de folhas (proteção local) de oito plantas de cada tratamento foram inoculadas com H. vastatrix. O K2SiO3 pulverizado no 3º par de folhas ou em um par de folhas da lateral esquerda foi ineficiente em aumentar a concentração de silício e reduzir a intensidade da esporulação (IE), o número total de pústulas (NTP) por folha e a severidade da ferrugem no 2º par de folhas ou no par de folhas da lateral direita, ao contrário do epoxiconazole e do ASM, os quais apresentaram sistemicidade na planta. A pulverização do K2SiO3 no 3º par de folhas também não garantiu, devido a sua natureza não sistêmica, redução da IE, do NTP e da severidade da ferrugem comparado com a proteção local. Os resultados desse trabalho apontam para a possibilidade de se utilizar a pulverização com silicato de potássio para reduzir a intensidade da ferrugem do cafeeiro preventivamente.

    Abstract in English:

    In the first experiment, coffee plants with three pairs of leaves were sprayed with potassium silicate (K2SiO3), epoxiconazole, acibenzolar-S-methyl (ASM), and distilled water in two different ways: spraying the 3rd pair of leaves from the apex and protecting the 2nd pair of leaves or spraying the two pair of leaves on the left side of the plant and protecting the pair of leaves on the right side. After 24 h, the abaxial surface of the protected pair of leaves was inoculated with Hemileia vastatrix. In the second experiment, the 3rd pair of leaves from the apex was sprayed with K2SiO3, ASM, and distilled water and the 2nd pair of leaves was protected. At 1, 5, 15, 25, and 35 days after products application, the abaxial surface of 2nd (systemic protection) and the 3rd pair of leaves (local protection) of eight plants per treatment were inoculated with H. vastatrix. The K2SiO3 spray on the 3rd pair of leaves or on the pair of leaves on the left side was ineffective in increasing silicon concentration and also decreasing the intensity of sporulation (IE), the total number of pustules (TNP) per leaf, and rust severity on the 2nd pair of leaves or in the pair of leaves on the right side, unlike the epoxiconazole and the ASM, which exhibited systemicity in the plant. The K2SiO3 sprayed in the 3rd pair of leaves also did not guarantee, due to its non-systemic action, reduction in the IE, TNP, and rust severity compared to its local protection. The findings of this study show the possibility of using potassium silicate spray to reduce the intensity of coffee leaf rust preventively.
  • Physical resistance of leaf sheaths of rice plants supplied with silicon and infected by Rhizoctonia solani Comunicações

    Schurt, Daniel Augusto; Rodrigues, Fabrício Ávila; Reis, Ricardo Dutra; Moreira, Wiler Ribas; Souza, Naiara Fernandes Abreu; Silva, Washington Azevedo

    Abstract in Portuguese:

    Este trabalho objetivou associar a deposição de silício (Si) nas bainhas de plantas de arroz ao aumento da resistência física à infecção por Rhizoctonia solani. Plantas das cultivares suscetíveis BR-Irga 409 e Labelle foram cultivadas em solução nutritiva contendo (+Si) ou não (-Si) Si. A concentração de Si nas bainhas das plantas supridas com Si e inoculadas com R. solani aumentou significativamente em relação às plantas não supridas com Si reduzindo o comprimento relativo da lesão às 96 horas após inoculação (hai). Houve diferença significativa entre os tratamentos -Si e +Si quanto à força necessária para uma agulha metálica atravessar as bainhas às 48 e 72 hai. A maior resistência física às 24 hai deve-se ao fato de que R. solani estava crescendo sobre o tecido sem destruí-lo, o que pôde ser comprovado pela ausência de sintomas. Após esse período, a resistência diminuiu devido ao rápido crescimento de R. solani. Entretanto, nas bainhas de plantas supridas com Si, a força necessária para a agulha penetrar foi maior às 48 e 72 hai. A resistência das bainhas de plantas supridas com Si à infecção por R. solani pode ser explicada, em parte, pela maior resistência física decorrente da deposição desse elemento.

    Abstract in English:

    This study aimed to associate the silicon (Si) deposition on sheaths of rice plants with an increase in physical resistance against infection by Rhizoctonia solani. Plants from the susceptible cultivars BR-Irga 409 and Labelle were grown in nutrient solution containing (+Si) or not (-Si) Si. Si concentration on sheaths of plants supplied with Si and inoculated with R. solani significantly increased compared to plants non-supplied with Si, reducing the relative lesion length at 96 hours after inoculation (hai). There were significant differences between -Si and +Si treatments for the force required of a metal needle to pass through the sheaths at 48 and 72 hai. The greater physical resistance at 24 hai was due to the fact that R. solani was growing on sheath tissue without destroying it, which could be proved by the absence of symptoms. After this period, the resistance decreased due to the rapid R. solani growth. However, on sheaths of plants supplied with Si, the force required for the needle to penetrate was higher at 48 and 72 hai. The sheath resistance of plants supplied with Si to infection by R. solani can be explained partly by the greater physical resistance due to Si deposition.
  • Occurrence of viruses in cowpea in the State of Paraíba, Brazil Comunicações

    Freitas, Aurivan Soares de; Cezar, Márcia Aparecida; Ambrósio, Márcia Michelle de Queiróz; Silva, Ana Kelly Firmino da; Aragão, Maria do Livramento; Lima, José Albérsio de Araújo

    Abstract in Portuguese:

    Visando verificar a ocorrência de vírus em cultivos de feijoeiro-caupi (Vigna unguiculata), foram realizadas visitas de inspeção a campos de produção dos municípios de Bom Sucesso, Paulista e Pombal, no estado da Paraíba, durante os meses de agosto a dezembro de 2009 e de fevereiro a maio de 2010. Amostras foliares com sintomas típicos de mosaico e deformação foliar foram coletadas e analisadas por "enzyme linked immunosorbent assay" (ELISA) indireto contra anti-soros específicos para Cowpea aphid-borne mosaic virus (CABMV) e Cucumber mosaic virus (CMV) e por dupla difusão em ágar contra anti-soro para Cowpea severe mosaic virus (CPSMV). Cinco amostras coletadas com sintomas de mosaico dourado no município de Pombal na época chuvosa foram submetidas à detecção molecular por meio de "Polymerase Chain Reaction" (PCR) para Begomovirus. A ocorrência de CPSMV e CABMV foi observada nos campos de produção dos três municípios visitados nas duas épocas de cultivo analisadas, em infecções simples e mistas. A presença de vírus do gênero Begomovirus foi confirmada em amostras foliares com sintomas de mosaico dourado. Entretanto, estudos adicionais serão necessários para a identificação da espécie. CMV não foi detectado em nenhum dos municípios analisados.

    Abstract in English:

    Visiting inspections were made in cowpea (Vigna unguiculata) fields in the counties Bom Sucesso, Paulista and Pombal, in the State of Paraíba, Brazil, during the period of August to December 2009 and February to May 2010 in order to verify the occurrence of virus. Leaf samples with typical symptoms of mosaic and leaf distortion were collected and tested by indirect "Enzyme linked immunosorbent assay" (ELISA) against antisera specific to Cowpea aphid-borne mosaic virus (CABMV) and Cucumber mosaic virus (CMV), and by double immune diffusion test to Cowpea severe mosaic virus (CPSMV) antiserum. Five samples collected in Pombal county during the rainy season showing golden mosaic were tested by Polymerase Chain Reaction (PCR) with primers to virus from the genus Begomovirus. The occurrence of CPSMV and CABMV was observed in the three counties in the two growing seasons in single and mixed infections. The presence of a virus from the genus Begomovirus was confirmed in leaf samples with golden mosaic, but further studies will be required to identify the species involved. The presence of CMV was not detected in any of the counties.
  • Partial resistance of old apple cultivars to Venturia inaequalis Comunicações

    Blanchet, Florian; Valdebenito-Sanhueza, Rosa Maria; Spolti, Piérri

    Abstract in Portuguese:

    Entre as práticas de manejo recomendadas para o controle da sarna da macieira (Venturia inaequalis), o uso de cultivares geneticamente resistentes assume grande importância em programa de manejo integrado, em que a restrição ao uso de fungicidas é comum. No presente estudo utilizaram-se técnicas de análise multivariada, com o objetivo de selecionar variáveis úteis nos programas de melhoramento e na classificação de cultivares de macieira quanto à resistência parcial a V. inaequalis. Dez cultivares originárias de material propagativo de plantas com idade entre 35 e 50 anos foram avaliadas. As cultivares CNPUV-09 e CNPUV-04 apresentaram nível de resistência similar à da cultivar Prima, padrão de resistência ao patógeno. A formação de estroma + apressório (ST + AP) e a esporulação (ESP) do patógeno após a inoculação com conídios em folhas das cultivares constituíram os maiores autovetores dos dois primeiros componentes principais e contribuíram com 23,9% e 28,5% da variância total, respectivamente. SP + AP e ESP apresentaram alta correlação com os eixos dos componentes principais. Essas variáveis podem ser úteis em programas de melhoramento de macieira para a seleção de cultivares com resistência parcial a V. inaequalis.

    Abstract in English:

    Among the practices recommended for apple scab (Venturia inaequalis) control, the use of genetically resistant cultivars is of great importance in integrated management programs, in which restrictions to fungicide use are common. In this study we used multivariate analysis techniques to identify variables useful in apple breeding programs for detecting partial resistance to V. inaequalis and to rank cultivars for this resistance type. A collection of ten old apple cultivars from propagative material 35 to 50 years old was evaluated for partial resistance to the pathogen. CNPUV-09 and CNPUV-04 had levels of resistance similar to that of cultivar Prima, the standard resistant cultivar. The stroma and apressorium (ST + AP) formation and sporulation (ESP) of the pathogen after a foliar inoculation by conidial suspension were the largest eigenvectors of the first and second principal components, and contributed with 23.9% and 28.5% of the total variance, respectively. ST + AP and ESP were highly correlated with first and second axes. These variables could be useful in apple breeding programs to select cultivars with partial resistance to V. inaequalis.
Sociedade Brasileira de Fitopatologia Sociedade Brasileira de Fitopatologia, SGAS 902 Edifício Athenas - Bl. B, Salas 102/103, 70390-020 Brasília - DF Brasil, Tel: (55 61) 3225-2421 - Brasília - DF - Brazil
E-mail: sbfito@sbfito.com.br