RESUMO
Tomato plants exhibiting typical symptoms of begomovirus infection, including leaf deformation, curling, and yellowing, were collected from cultivated fields in Lavalle Department, Corrientes, Argentina, in 2010. Although the number of affected plants was only 2% within a farm, the finding is of considerable importance since the white fly Bemisia tabaci is widely spread within the country, even in other southernmost areas such as the cinturón hortícola de Buenos Aires (horticultural belt around Buenos Aires). DNA isolated from infected tomato leaves collected from three symptomatic tomato plants was amplified by PCR with specific primers designed to amplify a region of component A and B of the Begomovirus genome (3). The amplified DNA fragment was sequenced and a new set of primers were designed based on the obtained sequences. A DNA fragment of about 1,300 bp was amplified and later the complete genome, which was 2,683 bp long. No fragments were obtained when template DNA was from non-infected leaf samples. The 2,683-bp fragment was annotated at the NCBI under Accession No. KC132844. Analysis by NCBI BLAST showed that it was highly homologous to DNA-A component of Begomovirus. Furthermore, the genome organization was typical of DNA-A component of bipartite New World begomovirus. The sequence had one open reading frame (ORF) on the viral-sense strand (AV1/CP) and four ORFs on the complementary-sense strand (AC1/Rep, AC2/TrAp, AC3/REn, and AC4). In order to confirm this finding, the viral genome was amplified by rolling circle amplification (RCA, TempliPhi 100 Amplification Kit, Amersham Biosciences) as described by the manufacturer instructions. The RCA full-length product was digested with XhoI generating a 2,700-bp DNA fragment, suggesting the presence of only one restriction site, in agreement with the bioinformatics analysis of the KC132844 sequence. This PCR product was used as template in PCR reactions with specific primers to DNA-A or DNA-B components. While the DNA-A primers generated the expected 1,300-bp fragment, those homologous to the DNA-B component did not generate amplifications. These results confirmed the identity of the DNA-A component of the isolate MT8. The full sequence of the DNA-A component was 94% homologous to the DNA-A sequence of the Uruguayan begomovirus Tomato Rugose Yellow Leaf Curl Virus-[U4.1] (JN381823.1). Therefore, considering our results and the criteria proposed by Fauquet (1), isolate MT8 is a new species of begomovirus described recently (2). This is the first report of TRYLCV in one of the main areas of tomato production in Argentina. This virus might be accompanying another begomovirus TYVSV that provoked yellow veins symptoms in tomato plants cultivated in the same area of Corrientes. These viruses appeared recently and concomitantly with the introduction of the white fly Bemisia spp. in the area, which is one of the main production areas of tomato and provides fresh tomatoes to the whole country, and in wintertime to the city of Buenos Aires, when the horticultural belt around Buenos Aires is not under production. References: (1) C. M. Fauquet et al. Arch Virol 153:783, 2008. (2) B. Márquez-Martín et al. Arch Virol 157:1137, 2012. (3) M. R. Rojas et al. Plant Dis. 77:340, 1993.
RESUMO
In 1995, fruiting tomato plants (Lycopersicon esculentum Mill. hybrid Tommy) from different commercial greenhouses near La Plata and near Chacabuco (Province of Buenos Aires) had symptoms similar those caused by Erwinia carotovora subsp. carotovora (1,4). Stems of the infected plants were rotted and produced adventitious roots. The cortex on the basal part of the stems turned black and sloughed off easily. The pith disintegrated and stems appeared hollow. Disease incidence of 2% was common, and nearly 10% of the plants in wetter areas of greenhouses were affected. Bacteria consistently isolated from diseased stems formed white-to-cream-colored colonies on yeast dextrose calcium carbonate agar (YDC). Bacteria from purified colonies were gram negative, oxidase negative, arginine dyhidrolase negative, catalase positive, methyl red positive, and facultatively anaerobic. Tests on four strains showed all fermented glucose, reduced nitrates to nitrites, and grew at a maximum temperature of 37 to 40°C. Strains did not hydrolyse starch nor utilize Tween 80. All strains were resistant to erythromycin in an antibiotic disk (15 µg) assay. Acid was produced from D(+)-glucose, D -mannitol, sucrose, D(+)-cellobiose, L(+)-rhamnose, L(+)-arabinose, D(+)-galactose, and D(+)-trehalose, but not from D-arabinose, D-sorbitol, and maltose. Bacteria utilized maleate and citrate but not propionate, benzoate, or malonate. The strains caused soft rot of pepper fruits and carrot slices within 24 h at 25°C. Pathogenicity was confirmed by needle stab inoculation at the primary leaf node on five plants each of 6-week-old greenhouse-grown tomato hybrids Presto and Parador. Inoculum was from 24-h-old cultures on YDC. Control plants were stab inoculated with needles dampened in sterile water. All plants were covered with polyethylene bags for 48 h at 25°C. Within 24 h after inoculation, watersoak and rot were detected; and during the next 48 h, plants wilted. Controls remained healthy. The bacterium was readily isolated from inoculated plants. Tests showed physiological characteristics identical to those of the bacteria used as inoculum. The pathogen was identified as Erwinia carotovora subsp. carotovora based on morphological, biochemical, and physiological characteristics and on pathogenicity. Reactions were identical to those of the type strain ATCC 15713 that had been included in all tests for comparison. Further identity was shown by polymerase chain reaction utilizing ERIC primers to generate DNA profiles (3). Profiles of the pathogen or the type strain were very similar to those from bacteria recovered from inoculated plants. This is the first known occurrence of a disease caused by Erwinia carotovora subsp. carotovora on greenhouse-grown tomato plants in Argentina, although it has been reported as causing soft rot of vegetables after harvest (2). References: (1) B. N. Dhanvantari and V. A. Dirks. Phytopathology 77:1457, 1987. (2) L. Halperin and L. S. Spaini. Rev. Arg. Agron. 6:261, 1939. (3) F. J. Louws et al. Appl. Environ. Microbiol. 60:2286, 1994. (4) D. E. Speights et al. Phytopathology 57: 902, 1967.
