June 10, 2005
Source: British Society for Plant Pathology, New Disease Reports, Vol. 11 [edited]
<http://www.bspp.org.uk/ndr/july2005/2005-42.asp>

A severe outbreak of melon yellow mosaic disease caused by zucchini yellow mosaic virus in the Punjab province of Pakistan
A.H. Malik, S. Mansoor, S. Iram, R.W. Briddon and Y. Zafar, National Institute for Biotechnology and Genetic Engineering, Jhang Road, Faisalabad, Pakistan. Accepted for publication 3 May 2005.

In 2003 a serious disease of muskmelon (_Cucumis melo_) appeared in commercial fields in the Punjab, Pakistan. Symptoms of the disease were characteristically chlorosis, leaf curling and deformation, vein clearing and the formation of leaf-like outgrowths on the upper leaf surface of some leaves. The disease led to almost 100 percent loss of the crop in some areas and was present again in 2004, with a similar phenotype and losses.

To identify the virus(es) associated with the disease, infected plant samples were collected from several locations in Punjab Province. On the basis of symptoms and host, cucurbit-infecting viruses were suspected. Samples were
screened for the presence of Zucchini yellow mosaic virus (ZYMV), and Cucumber mosaic virus (CMV) by DAS-ELISA using virus specific polyclonal antisera (Loewe, Germany). All symptomatic samples collected from the epidemic area were shown by DAS-ELISA to be infected with ZYMV.

For samples collected in the Punjab, CMV was detected at a low incidence in tomato plants expressing symptoms of yellow chlorosis growing near melon fields, but not in melon. Healthy indicator plants (melon, cucumber and
_Nicotiana benthamiana_) [Nb] were mechanically inoculated with sap extracted from symptomatic melon leaves by leaf abrasion. The virus was mechanically transmitted from infected samples to healthy melon seedlings, induced symptoms including leaf-like outgrowths on the upper leaf surface; typical of ZYMV infection.

No infection was observed in Nb, which is a diagnostic host for Watermelon mosaic virus, a common cucurbit potyvirus. This confirms that ZYMV is the causative agent of the melon disease.

Although ZYMV has been reported from Pakistan on some cucurbits, with an incidence of about 15 percent on samples collected from North West Frontier Province, we could not find a report of the virus infecting melons. Moreover, the enation [outgrowth]-like phenotype was observed for the 1st time and on a large scale in Pakistan, although this phenotype is known to be caused by ZYMV in other parts of the world. We are currently investigating ZYMV-encoded genes causing this phenotype.

References:
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Desbiez C, Lecoq H, 1997. Zucchini yellow mosaic virus. Plant Pathology 46, 809-829.

Ali A, Natsuaki T, Okuda S, 2004. Identification and molecular characterization of viruses infecting cucurbits in Pakistan. Journal of Phytopathology 152, 677-682.

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[ZYMV, first identified in Europe in 1981, has since been reported from most southern and southwestern states in the US as well as and has been found in France, the USA, Lebanon, Japan, Taiwan, Jordan, Singapore, Greece, Nepal and likely in other counties. It is one of the major members in the Potyvirus genus (_Potyviridae_ family) infecting cucurbits. It induces extreme symptoms on all melon types, including severe yellow mosaic on leaves, which is usually associated with distortion, deformation and fruit blistering. Plants are often stunted and fruit set is poor. The first few leaves affected on rockmelons may progress from chlorosis to full necrosis. A number of ZYMV variants have been described, some strains of which may induce lethal wilting, others can cause cracks on fruits or mosaic and hardening of the fruit flesh.

The virus has characteristics very similar to WMV-1 (Watermelon mosaic potyvirus) and Watermelon virus 2 (nonpersistent aphid transmission, etc.), and like WMV-2, its host range is not limited to cucurbits. Currently, none of the genetic factors that confer resistance to WMV-1 or WMV-2 are able to control ZYMV, but other resistance sources have been identified.

Links:
<http://www.dpi.qld.gov.au/horticulture/9575.html> <http://vegetablemdonline.ppath.cornell.edu/factsheets/Viruses_Cucurbits.htm>
<http://agri.upm.edu.my/~szakaria/MCB-MAPPS.html>
- Mod.DH]