Ocorrência de HLB e caracterização de Candidatus Liberibacter spp. no estado do Paraná

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

29/02/2012

RESUMO

Huanglongbing (HLB) is considered the most important disease for citrus production around the world. Three bacteria species are associated with HLB, ‘Ca. Liberibacter africanus’, ‘Ca. Liberibacter asiaticus’ and ‘Ca. Liberibacter americanus’. In Brazil, the disease was first reported in 2004, in the State of São Paulo. In Parana, HLB was reported for the first time in 2006, in the municipality of Altonia, in the Northeast region of the State. The objectives of this work were to verify the occurrence of the disease in different citrus growing areas of Parana, to study the genetic diversity of the bacterium present in the State, as well as to establish isolates of the bacterium in pure culture. Leaf samples from plants suspected to have HLB were examined by PCR with specific primers for the three species of ‘Ca. Liberibacter’. The study of the genetic diversity of the HLB bacterium present in Parana was carried out by PCR-RFLP using the restriction enzymes ApoI, HinfI e TaqI, and sequence analysis of the omp e rplAJ genes. For the isolation of ‘Ca. Liberibacter asiaticus’, branches of sweet Orange trees of cv. Valencia grafted onto Rangpur lime, as well non-grafted trees of the same cultivar were used. Sap was extracted by using the Scholander pressure pump. Fresh cut branches were subject to 3,0 mpascal of pressure and the sap was collected and plated onto the media BCYE, PD2+E e LiberA without addition of NADP. The Petri plates were kept in growth chamber at 28 ºC. The HLB survey was carried out during the period of August 2007 through August 2011. A total of 728 samples were examined, and 61.5% showed positive results for ‘Ca. Liberibacter asiaticus’. “Ca. Liberibacter asiaticus’ was the only species associated with HLB in Parana. Samples were collected from 192 orchards, comprising 47 municipalities of the North, Northeast and West regions of the State. HLB was detected in samples from 37 municipalities. In regard to citrus cultivars, HLB was detected in the sweet oranges Pera (50,0%), Valencia (17,7%), Iapar 73 (16,0%) and Folha Murcha (9,2%). Among the samples with positive results for HLB, 61.30% was of sweet Orange trees grafted onto Rangpur lime. The age of the citrus trees ranged from 0 to 20 years old, thus 34% of the samples were from trees 6 to 10 years old. HLB bacteria present in Parana did not show any genetic variability based on PCR-RFLP and sequencing analysis. The genetic similarity of the bacteria present in Parana was 99 to 100% similar to ‘Ca. Liberibacter asiaticus’ from other citrus growing areas. The presence of ‘Ca. Liberibacter asiaticus’ in bacterial colonies developed on PD2+E media was confirmed by PCR and sequence analysis. However, the presence of other bacteria 99% similar Paenibacillus spp. was determined by the sequence analysis of the 16S rDNA. These results indicated the possible association of ‘Ca. Liberibacter asiaticus’ with other bacteria in culture.

ASSUNTO(S)

bactérias fitopatogênicas - aspectos genéticos frutas cítricas - doenças e pragas cultura e meios de cultura (biologia) plantas - bacteriologia phytopathogenic bacteria genetic aspects citrus fruits diseases and pests plants bacteriology

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