Article

Ralstonia solanacearum em viveiros clonais de eucalipto no Brasil

Fitopatologia Brasileira 08/2006; 31(4). DOI: 10.1590/S0100-41582006000400005

ABSTRACT

solanacearum em viveiros clonais de eucalipto no Brasil. Fitopatologia Brasileira 31:357-366. 2006. RESUMO A incidência da murcha bacteriana, causada por Ralstonia solanacearum, em viveiros clonais de eucalipto, no período de abril a setembro de 2005, resultou no descarte de cerca de 553.991 minicepas, 6.837.691 propágulos na fase de enraizamento e 11.266.819 mudas, nos Estados da Bahia, do Espírito Santo, do Maranhão, de Minas Gerais e do Pará, totalizando um prejuízo estimado em, no mínimo, seis milhões de reais (US$ 2,7 milhões). Em minijardim clonal, a doença caracteriza-se por necrose foliar, escurecimento anelar ou completo do lenho, murcha e morte de minicepas. Os sintomas na parte aérea são similares à morte gradual de minicepas submetidas a podas drásticas ou com sistema radicular malformado. Na fase de enraizamento, miniestacas infectadas podem apresentar arroxeamento das nervuras do limbo foliar e podridão. No campo, a doença caracteriza-se por bronzeamento e necrose foliar, desfolha basal, ascendente escurecimento interno do lenho e morte da planta, geralmente a partir do quarto mês após o transplantio. Os sintomas geralmente se agravam em árvores com enovelamento de raízes e afogamento de coleto. A etiologia da doença foi confirmada por meio de testes de exsudação, microscopia de varredura, isolamento da bactéria, análises de PCR/RFLP, reação de hipersensibilidade (HR) em mudas de fumo, testes de patogenicidade em plântulas de eucalipto e tomate e re-isolamento da bactéria. Como o sistema de produção de mudas clonais de eucalipto é altamente favorável à multiplicação bacteriana e na falta de conhecimento sobre a resistência genética e de outras estratégias de controle da doença, é essencial evitar a introdução da bactéria em viveiros. Palavras-chave adicionais: murcha bacteriana, murcha vascular, Eucalyptus spp., propagação clonal, PCR/RFLP, DNA. ABSTRACT Ralstonia solanacearum on eucalyptus clonal nurseries in Brazil The occurrence of bacterial wilt caused by Ralstonia solanacearum in eucalyptus clonal hedges in the Brazilian states of Bahia, Espírito Santo, Maranhão, Minas Gerais and Pará, from April to September, 2005 resulted in loss of 553,991 rooted cuttings, 6,837,691 cuttings at rooting stage and 11,266,819 cuttings, with a total loss estimated to be at least six million reais (US$ 2.7 M). In clonal minihedges, the disease is characterized by foliar necrosis, annular or complete wood darkening, wilt and death of rooted-cuttings. Leaf symptoms are similar to those observed during the gradual death of rooted-cuttings subjected to drastic pruning or with malformed root systems. In the rooting phase, infected minicuttings can present redning of leaf blade veins and cutting rot. In the field, the disease is characterized by leaf browning and necrosis, basal leaf loss, internal wood darkening and plant death, with onset generally occurring four months after transplant. Disease severity is generally higher in trees with entangled roots and overplanting. The causal agent of the disease was confirmed through exudate tests, scanning electron microscopy, bacterial isolation, PCR/RFLP analyses, hypersensitive reactions (HR) in tobacco seedlings, pathogenicity tests in eucalyptus and tomato plantlets and reisolation of the bacteria. The production of cuttings offers a highly favorable environment for bacterial multiplication. This, combined with the lack of knowledge on genetic resistance and other disease control strategies, makes it essential to avoid introduction of this bacterium in clonal nurseries. Additional Keywords: bacterial wilt, vascular wilt, Eucalyptus spp., clonal propagation, PCR/RFLP, DNA. PCR/RFLP, DNA.

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    • "In all experiments we used R. solanacearum strain UFV32, which caused high levels of disease intensity on eucalypt in previous experiments. This strain was isolated from E. grandis in the region of Eunápolis, Bahia state (Alfenas et al. 2006) and characterized as belonging to biovar 1 and phylotype IIA (Fonseca et al. 2014). "
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    ABSTRACT: The variation in disease incidence of bacterial wilt caused by Ralstonia solanacearum among eucalypt clones (Eucalyptus spp.) in the field indicates that the disease may be controlled by planting resistant material. However, efficient inoculation methods for bacterial wilt on eucalypt are scarce and have low replicability. In this work, we developed an effective protocol for inoculation of R. solanacearum, which was subsequently validated on different eucalypt clones. Three methods were tested: (i) soil infestation with bacterial cell suspension; (ii) immersion of wounded roots in the bacterial cell suspension; and (iii) injection of bacterial cell suspension in the base of the stem. The injection method proved to be the most efficient for inoculating eucalypt with R. solanacearum. Differentiation between resistant and susceptible clones was observed 30 days after inoculation in independent assays. Base stem inoculation of 21 eucalypt clones showed that four clones, classified as resistant, did not exhibit wilt symptoms or bacterial ooze at the end of the experiment. Although no wilting symptoms were observed, four other clones were considered susceptible because at least one plant showed bacterial ooze from the inoculated tissue. The remaining 13 clones were highly susceptible, presenting typical wilt symptoms and bacterial ooze.
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    • "Considering the lack of knowledge about genetic resistance and strategies for controlling the disease, it is essential to prevent the introduction of new strains of the bacterium into the nurseries (Alfenas et al., 2006). It is therefore important to characterize the pathogen at subspecific level, since these strains could differ in spread rate, virulence, geographic distribution, range of host, and other attributes (Hayward, 1994; Fegan & Prior, 2005; Alfenas et al., 2006). Race 3 biovar 2 (R3bv2), known as the " potato race " , presents a limited range of natural hosts, being found in potato and occasionally in tomato (Solanum lycopersicum L.), eggplant (Solanum melongena L.) and sweet pepper (Capsicum annuum L.). "
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    ABSTRACT: In May 2007, potato plants exhibiting symptoms possibly of brown rot were collected in some potato fields in the Baixo Mondego region (Center), Portugal, as a part of a nationwide programme to monitor Ralstonia solanacearum. All laboratory procedures laid down in Commission Directive 2006/63/EC, including dilution plating on semi-selective medium SMSA, indirect imunofluorescence (UF), polymerase chain reaction (PCR) using specific primers and bioassays on tomato plants, were strictly followed and the causal agent of the disease was identified as Ralstonia solanacearum. The identity of the pure cultures of the isolated organism was confirmed by PCR, UF and pathogenicity tests on several other plant species (eggplant, tobacco, pelargonium and eucalyptus). In biovar determination, the failure of the isolates to utilise/oxidise certain carbon sources indicated that the isolates were all biovar 1. This biovar has a broader host range than biovar 2 strains, and affects several crops of economic importance including ornamental plants and forest trees. Comparative analysis of 16S rRNA and endoglucanase (egl) gene sequences of these isolates with sequences that have been deposited at the GenBank revealed a similarity higher than 99% for several Ralstonia solanacearum isolates from biovar 1, including isolate DAR 64836 (Accession number DQ011551). This is the first report of Ralstonia solanacearum biovar 1 in Portugal. All control measures specified in the Commission Directive are being implemented.
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