Further studies on two new tospoviruses in Brazil - Addition of zucchini lethal chlorosis tospovirus to the EPPO Alert List
In Brazil, the diversity of tospovirus species is increasing. Tomato spotted wilt tospovirus was initially reported in the 1940s, but during the last decades three more species were found: tomato chlorotic spot, groundnut ring spot and iris yellow spot tospoviruses. More recently, two more were reported one on chrysanthemum and another on courgette.
In 1994, growers in Atibaia county, São Paulo State, observed unusual symptoms on chrysanthemum. The virus was later designated as chrysanthemum stem necrosis tospovirus (EPPO Alert List). It also occurs in the Netherlands and recently it has been found on tomato crops in Minas Gerais, Brazil (see EPPO RS 96/082, 96/198, 98/130 and 99/094).
Another tospovirus initially designated as BR-09 and later as zucchini lethal chlorosis tospovirus (see EPPO RS 96/198) was observed in experimental fields of courgette (Cucurbita pepo cv. Caserta) in São Paulo State, in 1991. Infected courgettes showed symptoms of stunting and high yield losses of marketable fruits. Plants infected before flowering usually died within a few days. Plant infected after flowering showed similar symptoms, do not die but do not yield marketable fruits. Currently, large areas are affected by this virus which has spread from São Paulo State into central areas of Brazil (unspecified). A natural infection has been detected in a commercial field of cucumbers (Cucumis sativus cv. Hokushin) in the Federal District. Affected plants showed yellowing, mottling and vein banding on the leaves.
Further studies have been carried out in Brazil on these two viruses. Biological and molecular studies showed that they are two new distinct tospoviruses. In transmission experiments, Frankliniella occidentalis and F. schultzei transmitted chrysanthemum stem necrosis tospovirus, but not Thrips tabaci. Preliminary studies showed that F. schultzei is a highly efficient vector. All attempts to transmit zucchini lethal chlorosis tospovirus with these three thrips species failed. Recently a new thrips species, Frankliniella zucchini, has been described and identified as a vector of zucchini lethal chlorosis tospovirus in Brazil.
Zucchini lethal chlorosis tospovirus (a new tospovirus of courgette and cucumber)
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Why
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Zucchini lethal chlorosis tospovirus came to our attention because it was recently reported as causing a new and severe disease of courgette in Brazil, which can also affect cucumber.
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Where
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Brazil (São Paulo State, Federal District). It is reported to occur in central areas of Brazil but without further details.
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On which plants
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Courgette (Cucurbita pepo), cucumber (Cucumis sativus). More data is needed on the host range of this virus and in particular on the possible susceptibility of other Cucurbitaceae.
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Damage
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Infected courgettes showed symptoms of stunting and high yield losses of marketable fruits. Plants infected before flowering usually died within a few days. Plant infected after flowering showed similar symptoms, do not die but do not yield marketable fruits. Affected cucumbers showed yellowing, mottling and vein banding on the leaves (mortality is apparently not reported on this host).
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Transmission
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A new thrips species, Frankliniella zucchini, has been described and identified as a vector. The virus is not transmitted by Frankliniella occidentalis, F. schultzei and Thrips tabaci.
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Pathway
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Infected courgette or cucumber plants from Brazil (vegetables?).
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Possible risks
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Courgettes and cucumbers are important crops in the EPPO region. Symptoms are severe on courgettes, as plant mortality and high yield reduction is observed. However, more data is needed on the host range and epidemiology of the disease. So far, the vector Frankliniella zucchini has never been reported in the EPPO region.
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EPPO RS 99/180
Panel review date - Entry date 1999-11
Sources
Bezzera, I.C.; de Resende, O.; Pozzer, L.; Nagata, T.; Kormelink, R.; de Avila, A.C. (1999) Increase of tospoviral diversity in Brazil with the identification of two new tospovirus species, one from chrysanthemum and one from zucchini. Phytopathology, 89(9), 823-830.
Nagata, T.; de Resende, O.; Kitajima, E.W.; Costa, H.; Inoue-Nagata, A.K.; de Avila, A.C. (1998) First report of natural occurrence of zucchini lethal chlorosis tospovirus on cucumber and chrysanthemum stem necrosis tospovirus on tomato in Brazil. Plant Disease, 82(12), p 1403.
Nakahara, S.; Monteiro, R.C. (1999) Frankliniella zucchini (Thysanoptera: Thripidae), a new species and vector of tospovirus in Brazil. Proceedings of the Entomological Society of Washington, 101(2), 290-294.
Rezende, J.A.M.; Galleti, S.R.; de Resende, O.; de Avila, A.C.; Scagliusi, S.M.M. (1997) Incidence and the biological and serological characteristics of a tospovirus in experimental fields of zucchini in São Paulo State, Brazil. Fitopatologia Brasileira, 22(2), 92-95. (abst. on Internet: http://www.sbfito.com.br/sumario3.htm)