May 3, 2004
From: British Soc Plant Pathol, New Disease Reports [edited]

A new yellowing disease in Phaseolus vulgaris associated with a whitefly-transmitted virus
E Segundo, G Martin, IM Cuadrado, D Janssen Unidad de Virologia, IFAPA, Autovia del Mediterraneo s/n, 04745 La Mojonera, Spain. Accepted for publication 19 Mar 2004.

In the autumn of 2003, a new disease was observed in French bean (_Phaseolus vulgaris_) grown commercially in Spain. Symptoms resembling nutritional disorders consisted of interveinal mottling and yellowing in leaves, combined with stiffness or brittleness, were produced on the middle to lower parts of affected plants. Similar plants infested with whiteflies (_Bemisia tabaci_, [Bt]) were observed in greenhouses. Reproducible symptoms were observed when the virus was transmitted from bean to bean by Bt (9/10) but not by mechanical inoculation (0/30).

Electrophoresis of double-stranded (ds) RNA extractions from field-collected samples and Bt-inoculated plants revealed a high-molecular-weight dsRNA doublet, consistent with the bipartite genome of criniviruses (Celix et al, 1996). cDNA transcripts were produced and amplified by reverse transcriptase polymerase chain reaction (RT-PCR) from the agarose-purified dsRNA species by Uneven PCR (Chen and Wu, 1997). Individual amplicons were cloned into pGEM-T Easy Vector (Promega, WI, USA), sequenced and then analyzed using Blastx (NCBI, Bethesda, USA).

The nucleotide sequence and deduced amino acid sequence from one amplicon (GenBank accession AY543165) showed the highest percentage identity with the heat shock protein 70 homologue from members of the genus Crinivirus such as Cucurbit yellow stunting disorder virus (CYSDV) (respectively 57 per cent and 67 per cent), Beet pseudo-yellows virus (BPYV) (respectively 54 per cent and 63 per cent) and Tomato chlorosis virus (ToCV) (respectively 52 per cent and 57 per cent).

RT-PCR analysis with designed specific primers (forward primer 5 '-TTATGTATGATCTAGGCGGAGGTC-3' and reverse primer 5'-CTGGGTCAATGATACAAGTTAGTC-3') produced amplicon of the expected size (465 bp), when using total RNA extracts from diseased plants and viruliferous whiteflies.

This is the first report of a yellowing disorder in bean associated with a Bt-transmitted plant virus, with molecular and epidemiological features consistent with criniviruses (Wisler et al, 1998). Based on the host range and the unique partial genome sequence, we suggest the name bean yellow disorder virus (BnYDV) to describe this new virus.

References
Celix A, Lopez-Sese A, Almarza N, Gomez-Guillamon ML, Rodriguez-Cerezo E.
Characterisation of Cucurbit yellow stunting disorder virus, a Bemisia tabaci-transmitted closterovirus. Phytopathology 1996; 86: 1370-6.
Chen X, Wu R. Direct amplification of unknown genes and fragments by Uneven polymerase chain reaction. Gene 1997; 185: 195-9.
Wisler GC, Duffus JE, Liu H-Y, Li RH. Ecology and epidemiology of whitefly-transmitted closteroviruses. Plant Disease 1998; 82: 270-9.

[This report is of interest to plant virologists and is a good example of virus evolution. A host range test should be done to determine whether other food legumes monitored by ProMED-Plant (pea, chickpea, cowpea, lentil, peanut/groundnut and soybean) are susceptible to this virus. - Mod.DH]