Ocorrência, identificação e caracterização das espécies de xanthomonas, causadoras de mancha bacteriana em tomate para mesa no Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

Tomato bacterial spot is caused by at least four Xanthomonas species (Xanthomonas euvesicatoria, X. vesicatoria, X. perforans and X. gardneri), and is one of the most important diseases of both processing and fresh market tomato crops in Brazil. Eighty one isolates, collected from 23 commercial tomato fields, located in southern, southeastern, central-west and northeastern regions of the country, from 2005 to 2009, were identified to determine the occurrence of these species. These isolates were characterized through rep-PCR-based fingerprint analysis (BOX and REP-PCR), PCR with species-specific primers and pathogenicity tests on tomato and pepper susceptible varieties. Highest frequencies were observed for X. perforans (49.4%) and X. gardneri (40.7%). Only two isolates were X. euvesicatoria and six were X. vesicatoria. The occurrence of all four species was detected only in the southeast region of Brazil. All isolates were pathogenic on tomato. On pepper, only those of X. euvesicatoria and 30 isolates of X. gardneri caused bacterial spot symptoms. Isolates were also classified in races by avrRxv (present in race T1) and avrXv3-PCR amplification and by hypersensitive reaction on tomato genotype carrying the Xv3 gene. All X. perforans isolates induced hypersensitive response on this genotype, indicating that they belong to race T3, and in most cases confirmed by avrXv3-PCR. Xanthomonas vesicatoria and X. gardneri isolates were classified as race T2 since no PCR products were detected for avrRxv or avrXv3. Among the 81 isolates, races T1, T2 and T3 were identified, while races T4 and T5 of X. perforans were not detected. Sensitivity of all isolates to copper and streptomycin was evaluated by in vitro assays, with 50, 100 and 200 μg/mL of copper sulfate and 25, 50 and 100 μg/mL of streptomycin sulfate, with three replicates. Resistance was detected when bacterial growth was observed in all three replicates. None of the isolates was resistant to copper at 200 μg/mL. However, 97.53% were resistant to copper at 100 μg/mL and 98.77% were resistant to copper at 50 μg/mL. The frequencies of isolates resistant to streptomycin were 8.64% (100 μg/mL), 76.54% (50 μg/mL) and 83.95% (25 μg/mL). Isolates representing all four Xanthomonas species showed resistance, both to copper and streptomycin. This is the first survey and characterization of xanthomonads on fresh market tomatoes in Brazil.

ASSUNTO(S)

tomate bactérias patogênicas doenças e pragas outros produtividade agrícola produção de tomate brasil

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