J. C. Barbosa

Natural infection of Nicandra physaloides by Tomato severe rugose virus in Brazil.

Nicandra physaloides, a common weed in South America, was found to be infected by an isolate of Tomato severe rugose virus (ToSRV), a bipartite begomovirus. The plants developed severe yellow rugose mosaic and were collected in São Paulo State, Brazil. This isolate of ToSRV was transmitted by Bemisia tabaci B biotype from infected plants of N. physaloides to healthy plants of N. physaloides and tomato in a glasshouse. This is the first report of natural infection of N. physaloides by ToSRV in Brazil.

First report of Tomato chlorosis virus infecting tomato crops in Brazil.

During 2006 and 2007 in the region of Sumaré, state of São Paulo, Brazil, surveys were done on tomato (Solanum lycopersicum L.) virus diseases in three open field-grown crops. The data revealed low incidence (0.25 to 3.42%) of randomly distributed plants exhibiting interveinal chlorosis and some necrosis on the basal leaves. Symptoms were only observed on old fruit-bearing plants. Preliminary analysis of thin sections of symptomatic leaves from one plant by transmission electron microscopy revealed the presence of aggregates of thin, flexible, and elongated particles in some phloem vessels, suggesting infection with a member of the genus Crinivirus, family Closteroviridae. Total RNA was extracted separately from leaves of 10 symptomatic plants and used for one-step reverse transcription (RT)-PCR using the HS-11/HS-12 primer pair, which amplifies a fragment of 587 bp from the highly conserved region of the heat shock protein (HSP-70) homolog gene reported for Tomato infectious chlorosis virus (TICV) and Tomato chlorosis virus (ToCV) (1). The RT-PCR product was subsequently tested by nested-PCR for single detection of TICV and ToCV using primer pairs TIC-3/TIC-4 and ToC-5/ToC-6, respectively (1). Only one fragment of approximately 463 bp was amplified from 7 of the 10 plants with the primer pair specific for ToCV. No amplification was obtained with the primers specific for TICV. Two amplicons of 463 bp were purified and directly sequenced in both directions. Sequence comparisons of the 463-bp consensus sequence (GenBank Accession No. EU868927) revealed 99% identity with the reported sequence of ToCV from the United States (GenBank Accession No. AY903448) (3). Virus-free adults of Bemisia tabaci biotype B confined on symptomatic tomato leaves for a 24-h acquisition access period were able to transmit the virus to healthy tomato plants, which reproduced the original symptoms on the bottom leaves 65 days after inoculation under greenhouse conditions. Infection from transmission was confirmed by RT-PCR using the HS-11/HS-12 primer pair. In addition to B. tabaci biotype B, the greenhouse whitefly, Trialeurodes vaporariorum, has also been reported as a vector of ToCV, although it is less efficient than the B. tabaci biotype B in transmission of this virus (4). T. vaporariorum, which was previously considered limited to greenhouses, was recently reported in tomato and green bean (Phaseolus vulgaris L.) crops under field conditions in São Paulo State (2). Therefore, it might also contribute to the spread of ToCV in tomato crops in São Paulo. To our knowledge, this is the first report of ToCV in Brazil and South America. References: (1) C. I. Dovas et al. Plant Dis.86:1345, 2002. (2) A. L. Lourenção et al. Neotrop. Entomol. 37:89, 2008. (3) W. M. Wintermantel et al. Arch. Virol. 15:2287, 2005. (4) W. M. Wintermantel and G. C. Wisler. Plant Dis. 90:814, 2006.

Occurrence of Tomato chlorosis virus in tomato crops in five Brazilian states

Tomato chlorosis virus (ToCV) is a species in the genus Crinivirus, transmitted by Bemisia tabaci biotype B, first detected in Brazil in 2006 in the county of Sumare, State of Sao Paulo. During the period from 2007 to 2010, RT-PCR analyses followed by nested-PCR with specific primers for ToCV detection, and sequencing of the amplicons, confirmed the presence of this virus in samples of symptomatic tomato plants (Solanum lycopersicum) from crops in counties in the states of Bahia (BA), Espirito Santo (ES), Goias (GO), Minas Gerais (MG), and Rio de Janeiro (RJ). This is the first ToCV report for the states of BA, ES, GO, MG, and RJ, suggesting that this virus is widely disseminated in Brazil.

The importance of primary inoculum and area-wide disease management to crop health and food security

In some epidemics that have devastating consequences, the primary inoculum plays an important role in both epidemic onset and intensification. This article documents the dynamics of such epidemics, and illustrates their importance using two examples: Huanglongbing of citrus and begomoviruses of tomato. The latter disease is a major constraint to tomato production in Brazil, while the former has become a threat to global citrus production and farmers’ livelihoods. In spite of their importance little is known of the characteristics of these diseases and their management. This is because classical botanical epidemiology considers two types of diseases: polycyclic diseases, where the inoculum that causes infections is produced during the epidemic in or on individual plants that had been previously infected in the course of that epidemic; or monocyclic diseases, where inoculum that causes infection is not produced in or on individual plants that had been infected in the course of the epidemic, but in the soil, on secondary hosts, or in infected crop plants of the same host in other fields. Diseases of the first type typically present a logistic disease progress curve and management is based on reducing the rate of infection, whereas diseases of the second type present a monomolecular disease progress curve and management is based on reducing the initial inoculum. This article deals with plant diseases that depart in their structure and behaviour from these two archetypes, because they borrow elements from both. We address polycyclic diseases in which the primary inoculum has a continuous and dynamic role, and in which the secondary inoculum contributes to epidemic build-up, i.e., polycyclic diseases with continuous primary spread. This epidemiological structure generates less clear-cut disease progress curves, but usually follows a monomolecular dynamic. Our focus on this type of disease is multifold because (1) this more complex, combined, pattern is actually quite common, often leading to grave plant diseases epidemics, with impacts at the farm, community, and country scales, and (2) such epidemics are among the most difficult to manage. Our analysis leads us to assess past errors and current courses of action. It allows us to recognize, in addition to the conventional tools for management with local effects, the critical importance of collective action. Collective management action – at the farm, community, or national scales – is congruent with the characteristics of many epidemics, because they also entail properties at successive and nested scales. The management of such epidemics needs to address both the primary and secondary inoculum. More importantly, these actions have to be performed in an area-wide, regional basis in order to be effective.

Molecular characterization reveals Brazilian Tomato chlorosis virus to be closely related to a Greek isolate

Tomato chlorosis virus (ToCV, genus Crinivirus, family Closteroviridae) is a whitefly-transmitted crinivirus with a bipartite RNA genome. This virus is emerging as a serious threat to tomato crops worldwide. To date, only three complete genomic sequences of ToCV have been described from North America, Spain, and Greece isolates. In this study, we present the fourth complete nucleotide sequence of the RNA 1 (8594 nt) and RNA 2 (8242 nt) components of a Brazilian ToCV isolate (ToCV-BR). The complete genome sequences of RNA 1 and RNA 2 have been deposited in the GenBank database under the accession numbers JQ952600 and JQ952601, respectively. The sequences of RNA 1 and RNA 2 shares the highest nucleotide identity of 99.6% and 99.5%, respectively, with the Greek isolate sequences. Phylogenetic analysis confirmed that both RNA 1 and RNA 2 of the Brazilian isolate are most closely related to the Greek isolate of that virus. These results suggest that ToCV may have been recently introduced to Brazil from Europe.

Temporal and spatial dynamics of begomovirus disease in tomatoes in central Brazil

Over the last two decades, begomovirus diseases have increased in importance in Brazilian tomato crops. The major management strategy in Brazil is the application of insecticides to control the whitefly vector, but this is often unsuccessful. The objective of this work was to study the spatial and temporal progression of the disease in two processing tomato production areas in Central Brazil. A total of 24 plots (225 plants each) in six fields were evaluated weekly by visual inspection for plants with begomovirus symptoms. The predominant begomovirus in symptomatic tomato plants in all fields was Tomato severe rugose virus, and it was also detected in weeds and other crop plants. No correlation between incidence of begomovirus disease and whitefly population was found. The disease progression was rapid, with a slightly aggregated distribution of symptomatic plants. No relevant differences were observed in the temporal and spatial analyses, although an important difference was detected between plots located at the centre (PC) and the edge (PE) of the fields. In the temporal analysis, the begomovirus incidence and area under disease progress curve values were lower in PC than in PE. In the spatial analysis, plants with begomovirus symptoms were more aggregated in PC than in PE. These results suggest that the distribution of symptomatic plants in PC and PE could be a result of three dissemination mechanisms: one random (primary) and two aggregated, a real secondary spread, and a false secondary spread. The implications of these differences on disease management are discussed. This article is protected by copyright. All rights reserved.