NC State Watermelon Disease Handbook

Papaya Ringspot Virus Watermelon Strain (PRSV-W)

Disease:

Watermelon Strain of Papaya Ringspot Virus

Cause (pathogen):

Papaya Ringspot Virus Type W (PRSV-W)

Symtoms:

Prsv-w can cause severe plant stunting. On the leaves, a green mosaic or mottled pattern is usually accompanied by malformations, including puckering, blisters, leaf distortions, and narrow leaf blades. The youngest leaves are often reduced to just the main veins. Fruit is often malformed, and can have a color break pattern.

Source of primary inoculum:

Infected weed hosts in fencerows, wooded and non-cultivated fields.

Source of Secondary inoculum:

Virus particles produced in infected plants.

Spread:

Although PRSV-W is sap transmissible, it is spread primarily by aphids from infected cucurbitaceous weeds and crops. Leafminers also can transmit PRSV-W.

Disease cycle:

The aphids acquire and spread the viruses in a nonpersistent manner.

Control:

The major control strategies involve insecticides to eliminate the insect vectors, herbicides to remove alternate hosts, or genetic resistance. The most economical method for control of virus diseases is genetic resistance.

Microscopic Description:

Under the electron microscope the icosahedral particles are 28 nm in diameter.

Variants:

Prsv-w has 10 isolates.

Inoculum Increase:

Virus maintained in susceptible 'Gray Zucchini' squash plants.The host plants are grown in aphid-proof cages to prevent contamination of the plants by other viruses.The Rub method is used for inoculation.

Inoculum Preparation:

Collect young leaf tissue from zucchini 2-3 weeks after inoculation. Grind in 0.07 M phosphate buffer, pH 7.

Quantification:

None.

Host:

Citrullus lanatus, watermelon.

Source of Resistance:

Not reported.

Tissue Age:

Inoculate plants when plants reach the first true leaf stage.

Disease Response:

Two weeks after inoculation, plants are rated weekly for five weeks. The rating is on a scale of 0-9 (0=no symptoms, 9=dead plant). All plants that show resistance to the virus are inoculated again four weeks after the initial inoculation. Also plants that did not emerge by the first inoculation are inoculated at that time.

Procedures Developed by:

Todd C. Wehner
Dept. Hort. Sci., Box 7609
North Carolina State Univ.
Raleigh, NC 27695-7609