RESUMO

Tomato severe rugose virus (ToSRV) is one of Brazil's main begomoviruses infecting tomato (Solanum lycopersicum). Recent studies indicate that soybean (Glycine max) crops harboring the whitefly Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) may have epidemiological significance by acting as an asymptomatic amplifier host for the virus. In this study, we gathered experimental greenhouse and field evidence of the role of soybean in the epidemiology of the disease caused by ToSRV. Tomato and Nicandra physalodes, known as good sources of inoculum of this begomovirus, were used as references. The infection rates of soybean, tomato, and N. physalodes with ToSRV in greenhouse no-choice transmission tests with B. tabaci MEAM1 were 50, 71.4, and 64.2%, respectively. The transmission efficiencies of ToSRV to tomato when B. tabaci MEAM1 acquired the virus in ToSRV-infected soybean, tomato, and N. physalodes were 43, 33, and 20%, respectively. Leaves of ToSRV-infected soybean, tomato, and N. physalodes used as sources of inoculum had similar virus titers. In the host preference assay, viruliferous whiteflies preferred to land on tomato rather than soybean and N. physalodes, whereas aviruliferous whiteflies landed indistinctly on these plants. Under experimental field conditions, the transmission efficiency of ToSRV to tomato was higher when tomato was used as a source of inoculum, followed by N. physalodes and soybean. Considering that soybean is extensively cultivated in several Brazilian states that also grow tomato, it can serve as an efficient asymptomatic source of inoculum and support the recent hypothesis that it can also play, under certain conditions, a relevant role as an amplifier host in the epidemiology of the disease caused by ToSRV.

Assuntos

Begomovirus , Hemípteros , Solanaceae , Solanum lycopersicum , Animais , Glycine max , Begomovirus/genética , Produtos Agrícolas

RESUMO

Current control of tomato golden mosaic disease, caused in Brazil predominantly by tomato severe rugose virus (ToSRV), is dependent on both, planting resistant/tolerant hybrids and intensive insecticide sprays (two to three per week) for controlling Bemisia tabaci, the vector of ToSRV. Resistant hybrids only confer moderate resistance to infection by ToSRV and some tolerance to the disease. Insecticide sprays, although widely used, have failed in most tomato production areas in Brazil, as they are unable to reduce primary spread, i.e., infection caused by the influx of viruliferous whiteflies coming from external sources of inoculum. Severe epidemics are recurrently observed in some tomato fields in several Brazilian regions, which prompted us to postulate the existence in the agroecosystem, in some places and time, of amplifier hosts that provide the necessary force of infection for epidemics to occur, even in the absence of secondary spread in the target crop. Amplifier hosts are ideally asymptomatic, occur in high density near the target crop, and support growth of both virus and vector. Soybean and common bean are potential amplifier hosts for begomovirus in tomato crops. Our results support the hypothesis that soybean plants may play an important role as an amplifier host of ToSRV for tomato crops in the field, although this does not seem to be a frequent phenomenon. Successful amplification will depend on several factors, including the soybean cultivar, the soybean stage of development at the moment of infection, the ToSRV isolate, and the perfect synchrony between the beginning of a soybean field and the end of a ToSRV-infected crop, and, later, between the senescence of the ToSRV-infected soybean plants and the new tomato crop. The concept of amplifier hosts has been widely used in ecology of zoonoses but, to our knowledge, has never been used in botanical epidemiology.

RESUMO

Severe mosaic symptoms, accompanied by yellow spots, abnormally small leaves, fruit malformation and cracking, reduced plant growth, and high levels of whitefly (Bemisia tabaci MEAM1) infestation were observed in passionflower (Passiflora edulis) orchards in southwestern Bahia, Brazil. The aim of this work was to identify the species of begomovirus infecting the passionflowers, its prevalence in southwestern Bahia, and the spatial and temporal dynamics of the disease. Leaf samples from symptomatic plants collected at 57 orchards located in ten counties were evaluated by PCR for begomovirus infection. Complete nucleotide sequences of DNA-A for two isolates revealed 97 % identity with Passionfruit severe leaf distortion virus (PSLDV). The occurrence of PSLDV in 57 orchards was evaluated based on the presence of characteristic disease symptoms. Approximately 235,000 visually assessed plants exhibited symptoms characteristic of begomovirus infection. Epidemiological studies, conducted in two orchards in Dom Basílio County, showed that disease progress was relatively slow until 121 days after transplanting (DAT), but more rapid in the following 35 days, reaching 100 % infected plants by 156 DAT. The exponential model was fitted to the temporal dynamic of the disease for both areas. An aggregated pattern of diseased plants was predominant for almost all evaluations. It is possible that the primary and secondary spread of the pathogen occurred concurrently during the epidemic progression in both areas, especially late in the season. Containment measures to prevent the virus and the vector from spreading to other passionfruit producing areas in Brazil should be implemented.

RESUMO

Severe mosaic symptoms, accompanied by yellow spots, abnormally small leaves, fruit malformation and cracking, reduced plant growth, and high levels of whitefly (Bemisia tabaci MEAM1) infestation were observed in passionflower (Passiflora edulis) orchards in southwestern Bahia, Brazil. The aim of this work was to identify the species of begomovirus infecting the passionflowers, its prevalence in southwestern Bahia, and the spatial and temporal dynamics of the disease. Leaf samples from symptomatic plants collected at 57 orchards located in ten counties were evaluated by PCR for begomovirus infection. Complete nucleotide sequences of DNA-A for two isolates revealed 97 % identity with Passionfruit severe leaf distortion virus (PSLDV). The occurrence of PSLDV in 57 orchards was evaluated based on the presence of characteristic disease symptoms. Approximately 235,000 visually assessed plants exhibited symptoms characteristic of begomovirus infection. Epidemiological studies, conducted in two orchards in Dom Basílio County, showed that disease progress was relatively slow until 121 days after transplanting (DAT), but more rapid in the following 35 days, reaching 100 % infected plants by 156 DAT. The exponential model was fitted to the temporal dynamic of the disease for both areas. An aggregated pattern of diseased plants was predominant for almost all evaluations. It is possible that the primary and secondary spread of the pathogen occurred concurrently during the epidemic progression in both areas, especially late in the season. Containment measures to prevent the virus and the vector from spreading to other passionfruit producing areas in Brazil should be implemented.(AU)