Tropical Plant Pathology, Volume: 36, Issue: 3, Published: 2011
  • Comparison of inoculation methods for characterizing relative aggressiveness of two soybean sudden-death syndrome pathogens, Fusarium virguliforme and F. tucumaniae Articles

    Scandiani, María Mercedes; Ruberti, Delma S.; Giorda, Laura M.; Pioli, Rosanna N.; Luque, Alicia G.; Bottai, Hebe; Ivancovich, Juan J.; Aoki, Takayuki; O'Donnell, Kerry

    Abstract in Portuguese:

    Fusarium tucumaniae e F. virguliforme são agentes etiológicos primários da síndrome da morte súbita (sudden death syndrome - SDS) de soja na Argentina e nos Estados Unidos, respectivamente. Cinco isolados de F. tucumaniae e quatro isolados de F. virguliforme foram testados para agressividade relativa à soja, usando-se o método de ponta de palito de dente e duas versões do método de inoculação com solo infestado. A cultivar de soja parcialmente resistente RA629 e a cultivar suscetível A6445RG foram inoculadas separadamente com cada um dos nove isolados. Dois experimentos para cada método de inoculação foram realizados. A análise da variância identificou uma interação tripla significativa entre cultivar*experimento*patógeno SDS (P = 0,01), usando-se os três métodos. Quando os métodos de infestação de solo foram utilizados, F. virguliforme foi mais agressivo que F. tucumaniae. Entretanto, quando foi usado o método do palito de dente, isolados de F. virguliforme e F. tucumaniae foram igualmente agressivos. Embora os três métodos testados tenham discriminado níveis de resistência parcial dos genótipos à SDS, resultados do presente estudo indicam que inoculações no solo com grãos de sorgo infestados representam o melhor método para avaliação de resistência de cultivares de soja à SDS. A existência de interações entre o hospedeiro, patógeno e condições de ambiente destaca a necessidade de estudos adicionais para melhorar a reprodutibilidade de testes de seleção de germoplasmas de soja para resistência à SDS.

    Abstract in English:

    Fusarium tucumaniae and F. virguliforme are the primary etiological agents of sudden-death syndrome (SDS) of soybean in Argentina and the United States, respectively. Five isolates of F. tucumaniae and four isolates of F. virguliforme were tested for relative aggressiveness to soybean, using a toothpick inoculation method and two versions of a soil infestation inoculation method. Partially resistant soybean cultivar RA629 and susceptible cultivar A6445RG were inoculated separately with each of the nine isolates. Two experiments for each inoculation method were performed. Analysis of variance identified a significant three-way interaction of soybean cultivar*experiment*SDS pathogen (P = 0.01) using the different methods. When the two soil infestation methods were used, F. virguliforme was more aggressive than F. tucumaniae; however, when using the toothpick method, isolates of F. virguliforme and F. tucumaniae were equally aggressive. Although all three methods discriminated levels of partial resistance of the genotypes to SDS, results of the present study indicated that soil inoculations with sorghum infested grain represent the best method for evaluating soybean cultivar resistance to SDS. The existence of interactions among the host, pathogen and environmental conditions highlights the need for additional studies to improve the reproducibility of tests for screening soybean germplasm for resistance to SDS.
  • Evaluation of host susceptibility, pathogen aggressiveness and sporangial survival in soil as factors affecting incidence of potato tuber infection by Phytophthora infestans in Ecuador Articles

    Oyarzún, Pedro J.; Krijger, Anna-Karin; Garzón, Carla D.; Leon, Diego; Kromann, Peter; Yuen, Jonathan E.; Forbes, Gregory A.

    Abstract in English:

    Incidence of potato tuber infection by Phytophthora infestans is low in Ecuador. Factors considered to potentially affect the incidence of tuber infection include pathogen aggressiveness, host resistance, direct suppression from biological and chemical characteristics of soil acting on pathogen propagules, and exclusion resulting from soil structure and high ridging. In this study, we tested the hypothesis that low incidence could be due to reduced pathogen aggressiveness and/or low host susceptibility by comparing several pathogen isolates and commonly grown potato cultivars from Ecuador with isolates and cultivars from Europe, where tuber blight is known to be a problem. Additionally, in Ecuador, whole tubers and slices of common varieties were inoculated with local isolates of P. infestans to test for potential infection under Ecuadorian conditions. All isolates, regardless of origin, caused tuber infection. The aggressiveness of isolates varied, but this was both between and among Ecuadorian and Swedish isolates and it was not possible to establish a clear difference in the degree of infection based on isolate origin, or origin of potato variety. In general, we found no evidence to suggest that low aggressiveness of the pathogen or extreme resistance of the host explains low incidence of tuber blight in Ecuador. Therefore, we conclude that low incidence of tuber blight in Ecuador is probably caused by soil factors. Furthermore, exclusion due to soil structure and high hilling may play an important role as a preliminary soil infectivity study demonstrated that P. infestans sporangia were infective in six Ecuadorian field soils for at least 15 days.
  • Detection of a complex of viruses in tamarillo (Solanum betaceum) orchards in the Andean region of Colombia Articles

    Jaramillo, Margarita; Gutiérrez, Pablo Andrés; Lagos, Luz Estela; Cotes, José Miguel; Marín, Mauricio

    Abstract in Portuguese:

    Tomate de árvore (Solanum betaceum) é uma das principais fruteiras da região dos Andes da Colômbia. No entanto, devido à expansão de doenças virais, a área cultivada diminuiu-se rapidamente nos últimos anos. Neste trabalho, nós relatamos a identificação taxonômica de alguns dos vírus presentes nas principais regiões produtoras tomate de árvore na Colômbia. A presença de AMV, CMV, PLRV, Potyvirus, ToMV, TSWV e ToRSV foi avaliada pelo ELISA, nos estados de Antioquia, Boyacá, Cundinamarca, Nariño e Putumayo. Estes resultados foram complementados com RT-PCR e seqüenciamento do DNA das regiões correspondentes ao gene da proteína capsidial. Potyvirus, CMV e PLRV foram os vírus mais prevalentes, tendo sido cada um deles detectado em pelo menos uma amostra. Resultados do seqüenciamento mostram altos níveis de identidade dos isolado de PVY e PLRV obtidos de S. betaceum com isolados do vírus da batata, sugerindo a possibilidade de infecção cruzada. Os resultados confirmam a proposta de um complexo de vírus como responsável pela redução na produção do tomate de árvore na Colômbia.

    Abstract in English:

    Tamarillo is one of the main fruit crops in the Andean region of Colombia. However, due to expansion of viral diseases, the cultivated area has undergone a rapid decline during recent years. In this work, we report the taxonomical identity of some of the viruses present in the main tamarillo producing regions in Colombia. The presence of AMV, CMV, PLRV, Potyvirus, ToMV, ToRSV and TSWV was evaluated by ELISA in the provinces of Antioquia, Boyacá, Cundinamarca, Nariño and Putumayo. These results were complemented with RT-PCR and cDNA sequencing of the corresponding coat regions. Potyvirus, CMV and PLRV are the most predominant viruses, each virus being detected in at least one sample. Sequencing results revealed high levels of identity of PVY and PLRV from tamarillo with virus strains from potato crops, suggesting the possibility of cross infection. Our findings confirm that a virus complex is responsible for the decline of tamarillo productivity in Colombia.
  • Predicting population level of Delphacodes kuscheli, vector of Mal de Río Cuarto virus, and climate risk in the Argentine Pampas using meteorological models Articles

    Ornaghi, José A.; March, Guillermo J.; Moschini, Ricardo C.; Martínez, Malvina I.; Boito, Graciela T.

    Abstract in English:

    The planthopper Delphacodes kuscheli Fennah (Hemiptera: Delphacidae), principal insect vector of Mal de Río Cuarto virus on corn in Argentina, produces severe disease outbreaks when migration of large macropterous populations coincides with early corn growth stages. Linear models based on winter environmental variables were developed to explain variation of macropterous populations accumulated on oat until November 30 (1993-2001) in La Aguada (department of Río Cuarto, Córdoba, Argentina). Using daily records of maximum and minimum temperatures and precipitation, variables were generated and processed in different periods from June 1 to September 20. The best bivariate model (R²=0.97) had the lowest mean square error, was selected by Stepwise procedure, and its validation was highly satisfactory. It included the variable DDTxn, which accumulates mean temperature values exceeding 10°C on days with maximum and minimum temperature >24.5°C and 11°C, respectively, and DPr, which counts days with precipitation (>0mm). These variables were processed from July 1 to September 19. Using this model (correctly validated against independent observations in Chaján, Sol de Mayo and Espinillo -department of Río Cuarto- for 2, 3 and 7 years, respectively), climate risk in the Pampas region was evaluated relative to insect population levels in the endemic area.
  • Analysis of tomato seedling cell death in response to copper and paraquat induction Articles

    Rueda, Antoni; Roman, Yony; Lobo, Mario; Pelaez, Carlos

    Abstract in Portuguese:

    A pesquisa relacionada com a resposta inata das plantas á estresses tem atraído muito interesse por a similitude com as respostas reportadas nos mamíferos. Assim, foi proposta uma aproximação ás respostas de defesa aos estresses abióticos através da avaliação no modelo biológico Lycopersicon spp. da atividade enzimática caspase 10 em resposta da indução com CuCl2 y paraquat. Os ensaios da atividade caspase 10 mostraram um máximo de atividade na concentração 40 mM, 9 horas depois da elicitação, com uma pendente de 0,0054 e 0,0022 para L. hirsutum y L. esculentum respectivamente. A atividade comparativa dos genótipos sugere que, embora os dois genótipos presenteassem atividade, a resposta é menos variável de maior magnitude para L. hirsutum. A elicitação com paraquat presenteou a maior atividade caspase 10 em torno das 2 horas depois do estímulo, com uma pendente de 0,013 e 0,0012 para L. hirsutum y L. esculentum respectivamente. A determinação direita da atividade caspase 10 nas plântulas de tomate tratadas com cobre e paraquat, usando um substrato específico para mamíferos, mostrou que estes mecanismos estão relacionados provavelmente com processos de apoptose depois da indução abiótica.

    Abstract in English:

    Plant defense responses to stress have attracted interest because of their similarity to reported mammalian stress responses. To investigate plant responses to abiotic stress, caspase 10-like enzymatic activities of Lycopersicon hirsutum and Lycopersicon esculentum were assayed in response to copper chloride and paraquat induction. Caspase 10-like activity was greatest at 40 mM CuCl2 at 9 h after elicitation in both L. hirsutum and L. esculentum, for which respective response slopes (Δ absorbance per Δ minute) were 0.0054 and 0.0022 . The response for L. hirsutum was less variable and significantly greater than for L. esculentum. Elicitation of caspase 10-like activity by paraquat was greatest at around 2 h after treatment in both species with slopes of 0.013 and 0.0012, respectively for L. hirsutum and L. esculentum. The direct determination of caspase 10-like activity in tomato seedlings treated with copper and paraquat, using a specific substrate for mammals, suggested that the observed responses were related to apoptosis processes under abiotic induction.
  • Crop rotation in center-pivot for phytonematode control: density variation, pathogenicity and crop loss estimation Artigos

    Inomoto, Mário M.; Siqueira, Kércya M.S.; Machado, Andressa C.Z.

    Abstract in Portuguese:

    Estudo de campo realizado em três anos consecutivos, em propriedade agrícola com sucessão de cultura, irrigada por pivô central e infestada pelos nematoides Pratylenchus brachyurus, P. zeae, Meloidogyne incognita, Paratrichodorus minor, Helicotylenchus dihystera, Mesocriconema ornata e M. onoense, comprovou que o controle dos nematoides polífagos é muito difícil. Dentre as culturas implantadas durante o período (algodão, milho, soja e caupi), o algodão se destacou pelas perdas causadas por M. incognita e a soja por P. brachyurus. A exclusão do milho, por ser suscetível a ambos os nematóides, porém tolerante a M. incognita, beneficiaria as culturas de algodão, soja e caupi. Resultados obtidos em condições controladas confirmaram a patogenicidade de P. brachyurus a algodoeiro. O uso da resistência genética como componente do manejo mostrou-se válido para o binômio soja/M. incognita, embora prejudicado pela baixa resistência da soja a P. brachyurus. Concluiu-se que a sucessão de cultura precisa ser cuidadosamente planejada em áreas infestadas com nematoides polífagos, principalmente naquelas em que ocorrem mais de duas espécies patogênicas às culturas utilizadas.

    Abstract in English:

    A field study conducted over three consecutive years, on a farm using crop rotation system under center-pivot and infested with the nematodes Pratylenchus brachyurus, P. zeae, Meloidogyne incognita, Paratrichodorus minor, Helicotylenchus dihystera, Mesocriconema ornata and M. onoense, demonstrated that intensive crop systems provide conditions for the maintenance of high densities of polyphagous phytonematodes. Of the crops established on the farm (cotton, maize, soybean and cowpea), cotton and soybean suffered the most severe crop losses, caused respectively by M. incognita and P. brachyurus. Since maize is a good host for both nematodes, but tolerant of M. incognita, its exclusion from cropping system would be favorable to the performance of cotton, soybean and cowpea. Results from experiments carried out in controlled conditions confirmed the pathogenicity of P. brachyurus on cotton. Additional management with genetic resistance was useful in fields infested with M. incognita, although the soybean performance was affected by low resistance of the cultivars used for P. brachyurus. In conclusion, crop rotation must be carefully planned in areas infested with polyphagous nematodes, specifically in the case of occurrence of two or more major pathogenic nematodes.
  • Detection of 16SrII Group Phytoplasma in China Aster (Callistephus chinensis) Short Communications

    Win, Nang Kyu Kyu; Kim, Young-Hwan; Chung, Heewon; Jung, Hee-Young

    Abstract in English:

    China aster, Callistephus chinensis, is widely grown in Myanmar as an ornamental plant. Symptoms of flower virescence were observed in diseased China aster plants in Yezin, Myanmar. The presence of a phytoplasma was detected and identified by applying Polymerase Chain Reaction (PCR)/ Restriction Fragment Length Polymorphism (RFLP) techniques and sequencing the 16S ribosomal DNA. The phytoplasma was identified as belonging to ribosomal subgroup 16SrII-A, never reported before in China aster. It showed almost 100 % similarity with a 16S rDNA sequence of sunn hemp witches' broom phytoplasma (AB558143), which belongs to the peanut witches' broom phytoplasma group. This is the first record of China aster as a new host for a subgroup 16SrII-A phytoplasma.
  • Characterization of Meloidogyne incognita populations from São Paulo and Minas Gerais state and their pathogenicity on coffee plants Short Communications

    Oliveira, Dagoberto S.; Oliveira, Rosângela D'Arc Lima; Silva, Débora G.; Silva, Rodrigo V.

    Abstract in Portuguese:

    No Brasil, Meloidogyne incognita é considerado um dos fitonematóides mais agressivos e prejudiciais ao cafeeiro. Entretanto, populações desse nematóide, presentes em Minas Gerais, são incapazes de infectar esse hospedeiro. O objetivo deste trabalho foi caracterizar e avaliar a penetração e o desenvolvimento pós-infectivo de populações de M. incognita que diferem quanto à capacidade de infectar o cafeeiro. As duas populações foram confirmadas como M. incognita pelo fenótipo isoenzimático de esterase, I1, e PCR específico. Foram classificadas como raça 2 pela reação dos hospedeiros diferenciadores. Mudas de cafeeiro suscetível e resistente foram inoculadas com juvenis de segundo estádio (J2) de cada população e avaliadas quanto à penetração e desenvolvimento do nematóide a partir do segundo até o quadragésimo dia após a inoculação. A penetração de J2 da população de M. incognita de São Paulo foi maior do que a da população de Minas Gerais, tanto em cafeeiro suscetível (C. arabica 'Catuaí Vermelho IAC 44') quanto resistente (C. canephora 'Apoatã IAC 2258'). Como esperado, ocorreu maior penetração de J2 das duas populações de M. incognita no cafeeiro suscetível. Nas avaliações posteriores, somente foi observado desenvolvimento pós-infectivo nos indivíduos pertencentes à população de M. incognita de São Paulo em cafeeiro suscetível. Os mecanismos que conferiram incompatibilidade entre as populações de M. incognita de Minas Gerais e o cafeeiro atuaram principalmente na fase de penetração, mas também foi acompanhada pela ação de fatores de resistência pós-penetração que ocasionaram uma significativa emigração de J2 e impediram o estabelecimento do nematóide.

    Abstract in English:

    Meloidogyne incognita is one of the most aggressive and harmful plant-parasitic nematodes attacking coffee plantations in Brazil. However, populations from Minas Gerais state (MG) do not incite disease on coffee plants as strongly as populations from São Paulo state (SP). This study aimed to compare the capacity to incite disease on coffee plants from SP and MG-populations based on penetration and post-infective development of second-stage juveniles (J2) stage. Both populations were confirmed as M. incognita by using esterase phenotype I1 and species-specific PCR. Physiologically they were classified as race 2 by differential host test. Susceptible (C. arabica 'Catuaí Vermelho IAC 44') and resistant coffee seedlings (C. canephora 'Apoatã IAC 2258') were inoculated with J2 and assessed for penetration and development from 2nd to 40th day after inoculation. Although the penetration rate of the J2 from both populations was higher in susceptible than in resistant seedlings, the SP-population showed a higher penetration than the MG-population for both variables. Post-infective development proceeded only in individuals of the SP-population in susceptible seedlings. The incompatibility between the MG-population and coffee seedlings was evident at the penetration phase, which was also followed by post-penetration resistance factors leading to significant J2 emigration, impeding nematode establishment.
  • Variability of Puccinia sorghi in the core corn-growing region of Argentina

    Gonzalez, Mirian del Pilar; Eyherabide, Guillermo; Laguna, Irma Graciela

    Abstract in Spanish:

    La roya común causada por Puccinia sorghi es una de de las enfermedades endémicas de maíz (Zea mays) en Argentina. Se presenta cada año con diferentes niveles de severidad dependiendo del genotipo del hospedante, el biotipo del patógeno y las condiciones ambientales. Se estima una pérdida en el peso del grano entre 3 y 8% por cada 10% del total de área afectada. P. sorghi es un hongo heteroico que completa su ciclo en un hospedante alternativo: Oxalis spp. El ciclo completo se produce en las regiones con inviernos favorables. El objetivo de este estudio fue describir los factores involucrados en la virulencia del patógeno en la interacción Zea mays-Puccinia sorghi. Usando isolíneas Rp se identificaron 10 patotipos de P. sorghi, a partir de 16 aislamientos de diferentes localidades de la Provincia de Santa Fe (Oliveros, Venado Tuerto and Zavalla) y Buenos Aires (Pergamino). Se detectaron polimorfismos en el ADN por la metodología de RAPD en los diferentes aislamientos de P. sorghi. Estos experimentos muestran la heterogeneidad genética del patógeno en esta zona. Se determinó un alto consenso (81,4%) entre los resultados obtenidos a través de las isolíneas Rp y RAPD.

    Abstract in English:

    Common rust caused by Puccinia sorghi is one of the endemic diseases of corn in Argentina. It appears every year with different levels of severity depending on the genotype of the host, the biotypes of the pathogen, and the environmental conditions. Estimates of grain weight losses ranged from about 3 to 8% for 10% of the total leaf area affected. P. sorghi is a heteroic fungus that completes its cycle on an alternative host, Oxalis spp. Its complete cycle is feasible in mild winter regions around the world. The objective of this study was to describe the factors involved in the virulence of the pathogen in the interaction Zea mays-Puccinia sorghi. Using Rp isolines, 10 pathotypes of P. sorghi were identified from 16 isolates obtained from different locations in the provinces of Santa Fe (Oliveros, Venado Tuerto and Zavalla) and Buenos Aires (Pergamino). Polymorphisms in the DNA of the different isolates of P. sorghi from this core corn-growing region of Argentina were detected by RAPD methodology. These experiments showed the genetic heterogeneity of the pathogen in this area. A high consensus rate was determined (81.4 %) between the results obtained from the virulence biotypes and the results obtained by RAPD.
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