March 30, 2004
Source: British Society for Plant Pathology, New Disease Reports, Vol. 10 [edited] <http://www.bspp.org.uk/ndr/jan2005/2005-08.asp>

First report in Spain of a variant of tomato mosaic virus (ToMV) overcoming the Tm-22 resistance gene in tomato (_Lycopersicon esculentum_)
J. Aramburu and L. Galipienso Institut de Recerca i Tecnologia Agroalimentaries (IRTA) Ctra. de Cabrils s/n 08348, Cabrils, Barcelona, Spain. Accepted for publication 1 Apr 2005.

A naturally-infected tomato plant showing stunting and necrosis in the apical leaves was tested for viruses by enzyme-linked immunosorbent assay (ELISA) using polyclonal antisera (Loewe). The sample tested positive for
Tobacco mosaic virus (TMV) and Tomato mosaic virus (ToMV) and negative for Arabis mosaic virus, Cucumber mosaic virus, Pepino mosaic virus, Potato virus X, Potato virus Y, Tomato spotted wilt virus and Tomato bushy stunt virus.

Leaf extracts were not infective by mechanical inoculation to _Cucumis sativus_, and induced necrotic local lesions on _Datura stramonium_, _Petunia hybrida_, _Chenopodium quinoa_, _Nicotiana glutinosa_, _N. tabacum_ cv. _Xanthi_, and peppers (_Capsicum annuum_) cv. "Pekin" (Fito SA) and "Oman" (Seminis) which carry the L4 gene for resistance to Pepper mild mottle virus and TMV.

Systemic infections produced chlorotic mosaic in _Solanum nigrum_, tomatoes cv. "Marmande" and "Roma" and a non-resistant pepper hybrid C0103-4 (Fito SA), necrotic mosaic and stunting in tomatoes cv. "Bodar" and "Lisboa" (Seminis), ref. 537 (Fito SA) carrying the Tm-22 gene, and leaf and stem necrosis in peppers cv. "Delfos" (Fito SA), "Lido" and "Atlantic" (Seminis) carrying the L1 gene for TMV resistance.

A product of the expected size (419 nt) was amplified from nucleic acid extracts obtained from infected tomato cv. "Marmande" by reverse transcription-polymerase chain reaction (RT-PCR) using the primers 1F
(5'-TGCAGCAAAGGTAATAGTAG-3' position 1841-1860) and 1R (5'-CCGAACTTTTGACGAGTTTC-3' position 2280-2289), based on ToMV sequence AJ 417701 (NCBI).

Sequence analysis using BLAST (NCBI) showed 99.63 percent homology with ToMV strain L11A, (AB083196), which is able to overcome the resistance conferred by the tomato Tm22 gene (Yamamoto et al., 2002). No amplicons
were produced using TMV-specific primers designed from TMV sequence AJ 011933 (NCBI), suggesting the reaction to the TMV antiserum was due to a cross-reaction.

Important losses in pepper crops caused by ToMV have been reported in Spain (Alonso et al., 1989); however, this is the 1st report from Spain of a ToMV variant that overcomes the Tm22 resistance gene in tomato.

References:

Alonso E, Garcia Luque I, Avila Rincon MJ, Wicke B, Serra MT, Diaz Ruiz JR,  1989. A tobamovirus causing heavy losses in protected pepper crops in Spain. Journal of Phytopathology 125, 67-76.

Yamamoto H, Abe T, Ueda K, Inoue M, Matsumoto T, 2002. A missense mutation  in tomato mosaic virus L11A-Fukushima genome determines its symptomless systemic infection of tomato. Journal of General Plant Pathology 68, 385-389.

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[Tomato mosaic tobamovirus (ToMV), usually expresses characteristic mosaic symptoms, leading to considerable plant damage and yield losses. 3 resistance genes, Tm-1, Tm-2 and Tm-2(2) have been identified in crosses between wild and cultivated tomato species in efforts to prevent systemic infection and losses in fruit yield and quality caused by Tobacco mosaic virus (TMV) and ToMV. The Tm-2(2) resistance gene is used in most commercial tomato cultivars for protection against infection with tobacco mosaic virus (TMV) and its close relative tomato mosaic virus (ToMV). Observations suggest that the resistance conferred by the Tm-2(2) gene against ToMV depends on specific recognition events in this host-pathogen interaction rather than interfering with fundamental functions of the 30-kDa MP.

Links: <http://www.rug.nl/biologie/onderzoek/onderzoekgroepen/molecularbiologyofplants/
onderwijs/characterizationOfTheTomatoMosaicVirus>
<http://dpg.phytomedizin.org/ak/15/Tagung2005/Abstracts2005.htm#v12>
<http://jvi.asm.org/cgi/content/abstract/67/11/6432>
- Mod.DH]