Fitopatologia - Artigos
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11741
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Item Hipersensibilidade e necrose sistêmica em Nicotiana benthamiana transformada com o gene de resistência Sw- 5 de tomateiro(Fitopatologia Brasileira, 2006-05) Lau, Douglas; Oliveira, Julio Cezar F. de; Lau, Elene Y.; Brommonschenkel, Sérgio H.O gene Sw-5 do tomateiro confere resistência a várias espécies de tospovírus e codifica uma proteína contendo domínios de ligação a nucleotídeos e repetições ricas em leucina. Tomateiros com Sw-5 exibem reações necróticas nas folhas inoculadas com tospovírus. Estas reações e a estrutura da proteína Sw-5 indicam que a resistência ocorre por meio do reconhecimento do patógeno e desencadeamento da resposta de hipersensibilidade. A capacidade de Sw-5 de conferir resistência a tospovírus em tabaco selvagem (Nicotiana benthamiana Domin.) foi avaliada em plantas transgênicas. Uma construção com a seqüência aberta de leitura de Sw-5 e sua região 3 não-traduzida sob controle do promotor 35S do CaMV foi utilizada para transformação de N. benthamiana via Agrobacterium tumefaciens. Plantas de progênies R1 foram inoculadas com um isolado de tospovírus e avaliadas quanto à ocorrência de reação de hipersensibilidade e resistência à infecção sistêmica. Em uma progênie com segregação 3:1 (resistente:suscetível), foi selecionada uma planta homozigota e sua progênie avaliada quanto ao espectro da resistência a tospovírus. Plantas com o transgene exibiram resposta de hipersensibilidade 48 h após a inoculação, sendo resistentes à infecção sistêmica. O fenótipo da resistência foi dependente do isolado viral e um isolado de Tomato chlorotic spot virus (TCSV) causou necrose sistêmica em todas as plantas inoculadas, enquanto que isolados de Groundnut ringspot virus (GRSV) e um isolado relacionado a Chrysanthemum stem necrosis virus (CSNV) ficaram restritos ao sítio de infecção. Comparações do espectro da resistência obtido neste trabalho com aquele observado em outros membros da família Solanaceae indicam que as vias de transdução de sinais e as respostas de defesa ativadas por Sw-5 são conservadas dentro desta família e polimorfismos genéticos nas vias de transdução de sinais ou em componentes das respostas de defesa podem resultar em diferentes níveis de resistência.Item Etiology of bacterial leaf blight of eucalyptus in Brazil(Tropical Plant Pathology, 2008-05) Oliveira, José R.; Maffia, Luiz A.; Alfenas, Acelino C.; Gonçalves, Rivadalve C.; Lau, Douglas; Cascardo, Júlio C. M.Bacterial leaf blight of eucalyptus is initially characterized by water soaked, angular, amphigenous and interveinal lesions, concentrated along the main vein, at the edges or scattered on the leaf blade. As the disease progresses, the lesions become brown to pale, and when young leaves are infected leaf cut areas at the edges or perforations at the center of the lesions may appear due to abortion of the necrotic area. Eventually, necrosis may be found on petiole and twigs. Leaf fall commonly occurs on highly susceptible genotypes due to the early senescence of diseased leaves. Precise diagnosis is accomplished by bacterial exudation from leaf sections placed in a water drop under light microscope (200 x). Twenty-five bacterial isolates from Amapá (2), Bahia (4), Minas Gerais (2), São Paulo (9), Pará (3), Mato Grosso do Sul (1), and Rio Grande do Sul (4) States, which induced hypersensitive reaction (HR) in non-host plants and were pathogenic to eucalyptus, when inoculated by inoculum injection, were identified by biochemical assays, using carbon sources (MicroLogTM BIOLOG) and sequence analysis (16S rDNA). Ten isolates were identified as Xanthomonas axonopodis, four as X. campestris, four as Pseudomonas syringae, two as P. putida, two as P. cichorii, one as Erwinia sp., and two were similar to bacterial genera of Rhizobiaceae. When spray inoculated on intact plants of eucalyptus, only X. axonopodis, P. cichorii and isolates of the Rhizobiaceae family induced typical symptoms of the disease and were considered pathogenic. In Brazil, X. axonopodis seems to be the most widespread species causing the bacterial leaf blight of Eucalyptus spp.Item Etiology of bacterial leaf blight of eucalyptus in Brazil(Tropical Plant Pathology, 2008-05) Oliveira, José R.; Maffia, Luiz A.; Cascardo, Júlio C. M.; Alfenas, Acelino C.; Gonçalves, Rivadalve C.; Lau, DouglasBacterial leaf blight of eucalyptus is initially characterized by water soaked, angular, amphigenous and interveinal lesions, concentrated along the main vein, at the edges or scattered on the leaf blade. As the disease progresses, the lesions become brown to pale, and when young leaves are infected leaf cut areas at the edges or perforations at the center of the lesions may appear due to abortion of the necrotic area. Eventually, necrosis may be found on petiole and twigs. Leaf fall commonly occurs on highly susceptible genotypes due to the early senescence of diseased leaves. Precise diagnosis is accomplished by bacterial exudation from leaf sections placed in a water drop under light microscope (200 x). Twenty-five bacterial isolates from Amapá (2), Bahia (4), Minas Gerais (2), São Paulo (9), Pará (3), Mato Grosso do Sul (1), and Rio Grande do Sul (4) States, which induced hypersensitive reaction (HR) in non-host plants and were pathogenic to eucalyptus, when inoculated by inoculum injection, were identified by biochemical assays, using carbon sources (MicroLogTM BIOLOG) and sequence analysis (16S rDNA). Ten isolates were identified as Xanthomonas axonopodis, four as X. campestris, four as Pseudomonas syringae, two as P. putida, two as P. cichorii, one as Erwinia sp., and two were similar to bacterial genera of Rhizobiaceae. When spray inoculated on intact plants of eucalyptus, only X. axonopodis, P. cichorii and isolates of the Rhizobiaceae family induced typical symptoms of the disease and were considered pathogenic. In Brazil, X. axonopodis seems to be the most widespread species causing the bacterial leaf blight of Eucalyptus spp.Item Positioning of the major locus for Puccinia psidii rust resistance (Ppr1) on the Eucalyptus reference map and its validation across unrelated pedigrees(Tree Genetics & Genomes, 2010-06-12) Guimarães, Lucio M. S.; Mamani, Eva M. C.; Bueno, Nathalia W.; Faria, Danielle A.; Lau, Douglas; Alfenas, Acelino C.; Grattapaglia, DarioIn this report the major locus for Puccinia psidii rust resistance, Ppr1, was positioned on the reference genetic map for Eucalyptus. Additionally, its position was validated by association genetics in a related and two unrelated pedigrees involving different Eucalyptus grandis resistant trees crossed to individuals of two other species, Eucalyptus tereticornis and Eucalyptus camaldulensis. These results are consistent with the hypothesis that Ppr1 controls a large proportion of the variation for rust resistance, strengthening its role as a major locus in Eucalyptus and providing its unequivocal genomic position on linkage group 3. A localized map with 19 microsatellite loci was built around Ppr1. Multiallelic profiles were observed at several mapped microsatellites suggesting recent tandem duplications in the genomic landscape surrounding Ppr1. Markers EMBRA125 and EMBRA1071 flank Ppr1 at 9.5% and 7% recombination, respectively, and were found to be in linkage equilibrium in a E. grandis breeding population, consistent with the expectations in outcrossed Eucalyptus. Their potential use for MAS will specifically be directed to identifying resistant offspring of P. psidii resistant parent trees that are heterozygous at Ppr1. In these circumstances, a significant amount of LD is expected to occur between specific alleles at flanking microsatellites and the resistance allele at Ppr1. Moreover, the positional information of Ppr1 paves the way for prospective undertakings in this genomic region with the upcoming availability of a draft genome for E. grandis.Item Genetic control of Eucalyptus urophylla and E. grandis resistance to canker caused by Chrysoporthe cubensis(Genetics and Molecular Biology, 2010-09-01) Guimarães, Lúcio Mauro da Silva; Resende, Marcos Deon Vilela de; Lau, Douglas; Rosse, Leonardo Novaes; Alves, Alexandre Alonso; Alfenas, Acelino CoutoChrysophorte cubensis induced canker occurs in nearly all tropical and subtropical regions where eucalypts are planted, causing losses in both wood quality and volume productivity, especially so in the warmer and more humid regions of Brazil. The wide inter and intra-specific genetic variability of resistance to canker among Eucalyptus species facilitates the selection of resistant plants. In this study, we evaluated resistance to this pathogen in five Eucalyptus grandis (G) and 15 E. urophylla (U) trees, as well as in 495 individuals from 27 progenies derived from crosses between the trees. In the field, six-months-old test seedlings were inoculated with C. cubensis. Lesion length in the xylem and bark was measured eight months later. The results demonstrated that xylem lesions could preferentially be used for the selection of resistant clones. Eight trees (7 U and 1 G) were susceptible, and the remainder (8 U and 4 G) resistant. Individual narrow and broad sense heritability estimates were 17 and 81%, respectively, thereby suggesting that canker resistance is quantitative and highly dependent on dominance and epistasis.