A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases

June 11, 2003
Source: British Soc. Plant Pathol., Vol. 7 [edited]

Presence of lettuce big-vein disease and associated viruses in a subtropical area of Brazil

A Colariccio (Instituto Biologico, Centro de Pesquisa e Desenvolvimento de Sanidade Vegetal, Av. Cons.Rodrigues Alves 1252, 04014-002, Sao Paulo, Brazil); A.L.R. Chaves (as for Colariccio); ALR Chaves (as for Colariccio); M Eiras (as for Colariccio); CM Chagas (as for Colariccio; R Lenzi (Istituto di Virologia Vegetale, Strada delle Cacce 73, I-10135, Torino, Italy.); and P Roggero <p.roggero@ivv.cnr.it> (as for Lenzi). Accepted for publication 4 Jun 2003

Lettuce big-vein is a soil-borne viral disease characterized by vein clearing and leaf shrinkage resulting in plants of poor quality and reduced marketable value. The disease commonly occurs at temperatures below 20 deg. C, typical of temperate climates.

Recently, Mirafiori lettuce virus (MiLV), a possible ophiovirus, was found to be the causal agent of the disease, whereas the historically associated Lettuce big-vein virus (LBVV, genus Varicosavirus) causes only a latent infection (Roggero et al., 2003). No synergism has been observed between these serologically unrelated viruses, although both are transmitted by chytrid fungus, _Olpidium brassicae_.

MiLV has been detected in samples from several European countries, USA, and Japan. Mixed infection by both MiLV and LBVV are common in samples from lettuce (_Lactuca sativa_ L.) crops in northern Italy and France (Roggero et al., 2003). Molecular sequences for both viruses are now available (Sasaya et al. 2002; Van Der Wilk et al., 2002).

Recently, typical big-vein symptoms have been observed in Sao Paulo State, Brazil, on various lettuce cultivars grown both directly in soil or hydroponically. Symptoms were observed mainly during the cooler season, with day temperatures ranging from 18 to 22 deg C and night temperatures from 10 to 16 deg C.

Samples collected in different areas of Sao Paulo State (Biritiba-Mirim, Embu-Guacu, Guarulhos, Itapecerica da Serra, Mogi das Cruzes, Monte Alegre do Sul, Vargem Grande Paulista) were tested by DAS-ELISA with antisera specific for MiLV and LBVV (Roggero et al. 2003) and by negative-staining EM.

Most samples with big-vein symptoms tested positive by ELISA for both viruses and a few only for one. In EM, only LBVV virus particles were observed; virions were observed in only a few samples, confirming the
difficulty in EM visualization of both LBVV and MiLV particles.

Our surveys in this subtropical area of Brazil were similar to those in the temperate climate of Europe, where both viruses are commonly found. The presence of _O. brassicae_ was reported earlier in Brazil (Lin, 1979).

To our knowledge, this is the first report of the occurrence of lettuce big-vein disease and the associated viruses MiLV and LBVV in a sub-tropical area.

References
---------
Lin MT, 1979. Occurrence and host range of Olpidium brassicae in Central Brazil. Plant Disease Reporter 63, 10-12.

Roggero P, Lot H, Souche S, Lenzi R, Milne RG, 2003. Occurrence of Mirafiori lettuce virus and Lettuce big-vein virus in relation to development of big-vein symptoms in lettuce crops. European Journal of Plant Pathology, 109, 261-267.

Sasaya T, Ishikawa K, Koganezawa H, 2002. The nucleotide sequence of RNA1 of Lettuce big-vein virus, genus Varicosavirus, reveals its relation to nonsegmented negative-strand RNA viruses. Virology 297, 289-297.

Van Der Wilk F, Dullemans AM, Verbeek M, and Van Den Heuvel JFJM, 2002. Nucleotide sequence and genomic organization of an ophiovirus associated with lettuce big-vein disease. Journal of General Virology 83, 2869-2877.

[There are 2 surprises in this piece. Lettuce big-vein disease is caused by Mirafiori lettuce ophiovirus (MiLV), not by Lettuce big-vein varicosavirus (LBVV), and the disease occurs in a sub-tropical region (Brazil). Virion morphologies are similar to those of Tenuiviruses, and their internal structures are similar to those of Bunyaviruses. MiLV-infected lettuce is less marketable, thus imposing an economic burden on growers.

Additional reference:
---------------
Roggero et.al. Occurrence of Miafiori lettuce virus and Lettuce big-vein virus in relation to development of big-vein symptoms in lettuce crops. European J. Plant Pathol. 109:261-267, 2003 <http://www.kluweronline.com/issn/0929-1873/contents>
- Mod.DH]