Taxonomic Repositioning of Xanthomonas campestris pv. viticola (Nayudu 1972) Dye 1978 as Xanthomonas citri pv. viticola (Nayudu 1972) Dye 1978 comb. nov. and Emendation of the Description of Xanthomonas citri pv. anacardii to Include Pigmented Isolates Pathogenic to Cashew Plant.

Grapevine bacterial canker, which is caused by Xanthomonas campestris pv. viticola, is one of the most important grapevine diseases in the northeastern region of Brazil. This disease causes severe damage and represents a high potential risk to the development of Brazilian viticulture. In turn, pigmented isolates pathogenic to cashew plant, making cashew fruit unfit for sale, also have been detected in Northeastern Brazil. Given that the taxonomic position of these bacteria is unclear, the multilocus sequence analysis (MLSA) technique, average nucleotide identity (ANI) values and tetranucleotide frequency correlation coefficients (TETRA) were used to analyze their phylogenetic relationship in relation to other Xanthomonas species. X. campestris pv. viticola was closely related to X. citri pv. mangiferaeindicae (repetitive-polymerase chain reaction [rep-PCR], MLSA, and ANI) and X. citri subsp. citri (MLSA and ANI). Pigmented isolates pathogenic to cashew plant were closely related to X. citri pv. anacardii (rep-PCR, MLSA, ANI, and TETRA). The results obtained in this study support the emendation of the description of X. citri pv. anacardii to include pigmented isolates of Xanthomonas pathogenic to cashew plant. In addition, the reclassification of X. campestris pv. viticola as X. citri pv. viticola comb. nov. is suggested.

Molecular detection of Erwinia psidii in guava plants under greenhouse and field conditions / Detecção molecular de Erwinia psidii em goiabeira em condições de casa de vegetação e campo

ABSTRACT: Erwinia psidii causes bacterial blight of guava ( Psidium guajava ), an important disease of this crop in Brazil. The pathogen affects branches and twigs of guava trees, reducing yield significantly. Bacterial dissemination often occurs through contaminated but asymptomatic propagating plant material. The objectives of this research were to evaluate the use of BIO-PCR and conventional PCR to detect E. psidii in inoculated guava plants grown in a greenhouse and in symptomatic and asymptomatic trees from guava orchards. Erwinia psidii strain IBSBF 1576 was inoculated (107CFU mL-1) into young guava shoots and plant tissue was analysed at 0, 5, 10, and 15 days after inoculation. Symptoms were observed after 5 days and all inoculated shoots were PCR positive at all times, by both BIO-PCR and conventional PCR. Under natural infection conditions, 40 samples were tested by BIO-PCR from each of three guava orchards, 20 showing symptoms and 20 asymptomatic. PCR was positive for 58 out of 60 symptomatic samples (96.7%) and for 6.7% of asymptomatic samples, showing that the method can be used to detect the pathogen at early stages of infection. This PCR method may be used as a diagnostic tool to assess bacterial survival, dissemination and disease outbreaks.

RESUMO: Erwinia psidii é o agente causal da seca dos ponteiros da goiabeira ( Psidium guajava ), uma importante doença dessa cultura no Brasil. O patógeno afeta folhas, frutos, ramos e brotações, reduzindo significativamente a produtividade da cultura. A disseminação do patógeno ocorre por meio de material propagativo contaminado, porém assintomático. Os objetivos do trabalho foram avaliar o uso da BIO-PCR e da PCR convencional para detectar E. psidii em plantas inoculadas em casa de vegetação e em plantas sintomáticas e assintomáticas em pomares de goiabeira. A estirpe IBSBF 1576 de E. psidii foi inoculada (107UFC mL-1) em brotações novas de mudas de goiabeira e o tecido foi analisado nos tempos 0, 5, 10, e 15 dias após a inoculação. Sintomas foram observados após 5 dias e todas as plantas inoculadas foram positivas por PCR em todos os tempos avaliados, pelos dois métodos (BIO-PCR e PCR convencional). Sob condições de infecção natural em campo, três pomares foram avaliados por BIO-PCR. De cada pomar, foram coletadas 40 amostras, sendo 20 com e 20 sem sintomas. PCR foi positiva para 58 das 60 amostras sintomáticas (96,7%) e para 6,7% das amostras assintomáticas, demonstrando que o método pode ser usado para detectar o patógeno nos estágios iniciais da infecção. Este método poderá ser útil como uma ferramenta para a diagnose e para monitorar a sobrevivência e disseminação da bactéria e, consequentemente, novos focos da doença.