Distribuição de Candidatus Liberibacter americanus e Candidatus Liberibacter asiaticus em plantas cítricas
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Data
2009-11-27
Autores
Sousa, Michele do Carmo de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A severidade dos sintomas provocados pelo Huanglongbing (HLB) ou Greening, a rápida progressão na incidência de plantas afetadas nos pomares e o fato de esta doença afetar indistintamente todas as variedades comerciais de citros, contribuíram para este estudo que visou conhecer o padrão de colonização da bactéria Candidatus Liberibacter americanus (Lam) e Candidatus Liberibacter asiaticus (Las) em plantas cítricas. O PCR convencional é o teste atualmente utilizado na diagnose. Apesar de ser uma técnica reconhecidamente sensível, para o caso do HLB tem sido apenas confirmatório, ou seja, somente permite detecção da presença da bactéria em amostras de folhas sintomáticas. Surgiram aprimoramentos da técnica de PCR, como é o caso do Nested PCR e o PCR quantitativo (qPCR), demonstrado neste trabalho ser o método empregado mais sensível que o PCR convencional. Assim, através deste estudo pode-se concluir que Las e Lam se concentraram prioritariamente nas partes com sintomas de HLB das plantas de campo, naturalmente inoculadas e infectadas por liberibacter, se diferenciando na média do número estimado de cópias de liberibacter por grama de folha de plantas afetadas, sendo Las com 5,63 contra 5,01 em plantas afetadas por Lam (título bacteriano). A proporção de amostras positivas para Lam foram de 21 (19%) contra 12 (11,2%) amostras positivas para Las. A maior parte das amostras foi negativa para ambas as liberibacters (96 – Las e 90 – Lam). O pequeno acréscimo nos resultados positivos obtido pelo método de qPCR, aliado ao seu alto custo, não justifica a substituição do PCR convencional por este método na diagnose laboratorial do HLB, ficando restrito somente a pesquisa
The degree of severity of the symptoms developed by Huanglongbing (HLB) or Greening, the fast incidence of diseased plants at different orchards and the fact that this phytopathogen affects various commercial citrus varieties have contributed to the proposition of the present work, that aimed to know the colonization pattern developed by the bacteria Candidatus Liberibacter americanus (LAM) and Candidatus Liberibacter asiaticus (LAS) on citrus plants. The conventional PCR is the current used assay to detect HLB. Besides being a sensitive and specific technique it is currently seen and a molecular technique that confirms the already symptomatic leaves of diseased plants. Improvements of the PCR technique named the Nested PCR and the quantitative PCR is described in this work as the most sensitive to detect the phytopathogen prior to the development of the symptoms disease. So, based on the results obtained in this work it was possible to conclude that LAS and LAM concentrate showed a tendency to appear mostly on parts of the plants exhibiting symptoms and that are already infected by these bacteria, showing difference when mean number of copies of liberibacter per g of leaf of infected plants, with LAS value of 5.63 as compared to 5.01 for LAM on plants with LAM detectable symptoms (high bacterial titer). The ratio of LAM positive samples was 21 (19%) against 12 (11.2%) positive for LAS. The majority of the samples were detected as negative for both bacteria (96% for LAS and 90% for LAM). The small increase on the positive results obtained when qPCR was used and considering its present high analysis cost, this type of PCR is not seen as adequate to diagnose LAM or LAS
The degree of severity of the symptoms developed by Huanglongbing (HLB) or Greening, the fast incidence of diseased plants at different orchards and the fact that this phytopathogen affects various commercial citrus varieties have contributed to the proposition of the present work, that aimed to know the colonization pattern developed by the bacteria Candidatus Liberibacter americanus (LAM) and Candidatus Liberibacter asiaticus (LAS) on citrus plants. The conventional PCR is the current used assay to detect HLB. Besides being a sensitive and specific technique it is currently seen and a molecular technique that confirms the already symptomatic leaves of diseased plants. Improvements of the PCR technique named the Nested PCR and the quantitative PCR is described in this work as the most sensitive to detect the phytopathogen prior to the development of the symptoms disease. So, based on the results obtained in this work it was possible to conclude that LAS and LAM concentrate showed a tendency to appear mostly on parts of the plants exhibiting symptoms and that are already infected by these bacteria, showing difference when mean number of copies of liberibacter per g of leaf of infected plants, with LAS value of 5.63 as compared to 5.01 for LAM on plants with LAM detectable symptoms (high bacterial titer). The ratio of LAM positive samples was 21 (19%) against 12 (11.2%) positive for LAS. The majority of the samples were detected as negative for both bacteria (96% for LAS and 90% for LAM). The small increase on the positive results obtained when qPCR was used and considering its present high analysis cost, this type of PCR is not seen as adequate to diagnose LAM or LAS
Descrição
Palavras-chave
Cítricos, Reação em cadeia de polimerase, Greening, Huanglongbing, Citrus, Quantitative PCR
Como citar
SOUSA, Michele do Carmo de. Distribuição de Candidatus Liberibacter americanus e Candidatus Liberibacter asiaticus em plantas cítricas. 2009. xiii, 53 f. Dissertação (mestrado) - Universidade Estadual Paulista, Faculdade de Ciências Agrárias e Veterinárias, 2009.