August 9, 2004
From: ProMED-mail<promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of cucurbit aphid-borne yellows virus in Spain

M. Juarez, Escuela Politecnica Superior de Orihuela, Universidad Miguel Hernandez de Elche, Ctra. de Beniel km 3.2, 03312 Orihuela, Alicante, Spain; and V. Truniger and M. A. Aranda, Centro de Edafologia y Biologia Aplicada del Segura (CEBAS), Consejo Superior de Investigaciones Cientificas, Campus Universitario de Espinardo, 30100 Espinardo, Murcia, Spain. Plant Dis. 88:907, 2004; published on-line as D-2004-0527-01N, 2004. Accepted for publication 17 May 2004.

In late spring 2003, field-grown melon plants (_Cucumis melo_ L.) showing bright yellowing of older leaves were observed near Valladolises in Campo de Cartagena, Murcia, Spain.

Symptoms resembled those caused by viruses of the genus Crinivirus (family _Closteroviridae_), but absence or very low populations of whiteflies were observed. However, diseased foci showed clear indications of heavy aphid infestations. Later, during the fall of 2003, squash plants (_Cucurbita pepo_ L.) grown in open fields in the same area showed similar symptoms.

Tissue print hybridizations to detect Cucurbit yellow stunting disorder virus (CYSDV) and Beet pseudo yellows virus (BPYV) in symptomatic samples were negative. CYSDV and BPYV are 2 yellowing-inducing criniviruses previously described in Spain. In contrast, standard double-antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISA) with antiserum against Cucurbit aphid-borne yellows virus (CABYV; genus _Polerovirus_, family
_Luteoviridae_) that was kindly provided by H. Lecoq (INRA-Montfavet Cedex, France) were consistently positive.

Definitive confirmation of CABYV associated with symptomatic samples was obtained by performing reverse-transcription polymerase chain reaction (RT-PCR) analyses for the CABYV coat protein gene. Total RNA extracts (TRI reagent; Sigma Chemical, St. Louis, MO) were obtained from symptomatic and asymptomatic leaf samples and RT-PCR reactions were carried out using the primers
5(prime)-GAATACGGTCGCGGCTAGAAAC-3(prime) (CE9) and
5(prime)-CTATTTCGGGTTCTGGACCTGGC-3(prime) (CE10) based on the CABYV sequence published by Guilley et al. (2).

A single DNA product of approximately 600 bp was obtained only from symptomatic samples. Amplified DNA fragments from 2 independent samples (samples 36-2 and 37-5) were cloned in _E. coli_ and sequenced (GenBank accession Nos. AY529653 and AY529654). Sequence comparisons showed a 95 percent nucleotide sequence identity between the 2 sequences. A 97 percent and 94 percent nucleotide sequence identity were found among 36-2 and 37-5, respectively and the CABYV sequence published by Guilley et al. (2).

CABYV seems to be widespread throughout the Mediterranean Basin (1,3), but to our knowledge, it has not previously been described in Spain. Additionally, our data suggest that significant genetic variability might be present in the Spanish CABYV populations.

References:
(1) Y. Abou-Jawdah et al. Crop Prot. 19:217, 2000.
(2) H. Guilley et al. Virology 202:1012, 1994.
(3) H. Lecoq et al. Plant Pathol. 41:749, 1992.

[CABYV, an aphid-borne luteovirus persistently transmitted by several aphid species (_Aphis gossypii_ and _Myzus persicae_), was first recorded in France in 1992 and has subsequently spread to Morocco, Sudan, and Zambia. It has a narrow host range. Major vegetable species susceptible to CABYV include watermelon (_Citrullus lanatus_), muskmelon (_Cucumis melo_), cucumber (_C. sativus_), zucchini squash (_Cucurbita pepo_), and lettuce (_Lactuca sativa_).
Yield reduction in infected cucumber crops can reach 50 percent.

According to Abou-Jawdah and colleagues at American University, Beirut and INRA, France, viral diseases are the major cause of economic losses in commercial cucurbit production in Lebanon. A survey revealed that Zucchini yellow mosaic potyvirus (ZYMV) and Cucurbit aphid-borne yellows polerovirus (CABYV) are the most common viruses of field-grown cucurbits in Lebanon.

Other viruses involved were Watermelon mosaic potyvirus (WMV), Papaya ringspot potyvirus-watermelon strain (PRSV-W) and Cucumber mosaic cucumovirus (CMV).

Inoculation of squash with a mild strain of ZYMV (strain WK) gave significant protection against severe virus symptoms and resulted in significant yield increase as compared to the control, as did silver plastic mulch. The best protection and highest total yield were obtained with floating row covers (flexible nets or other types of screens). Integration of cross-protection with silver mulch or floating row covers improved the protection obtained with either approach. Cross-protection is still a useful disease management option for reducing yield loss and maintaining reasonable quality of product. Resistant curcubit cultivars are not available, but sources of resistance to CABYV have been identified in melon accessions.

Other references:
<http://www.iita.org/info/virology/pdf_files/213-232.pdf>
Y. Abou-Jawdah, H. Sobh, S. el-Sammar, A. Fayyad, and H. Lecoq. 2000.
Incidence and management of virus diseases of cucurbits in Lebanon.
Crop Protection, Vol. 19 (4) 217-224.
- Mod.DH]