Beijing Normal University, Beijing, China

Zucchini yellow mosaic virus (ZMV) is one of the most destructive pathogens infecting cucurbits in many areas of the world. It is a recognized member of the potyvirus group and causes severe disease in many cucurbit species. This paper reports the biological and serological properties of an isolate of ZYMV in the Xinjiang area of China.

Materials and methods
Zucchini yellow mosaic virus-Xinjiang (ZMV-XJ) was isolated from a diseased muskmelon (Cucumis melo var. Hami) and maintained in pumpkin (Cucurbita pepo). At least 10 test plants of each species belonging to nine families were inoculated for a host-range test. Leaf dips of infected tissue were prepared on grids and were negatively stained for examination with an electron microscope. For thin sectioning, infected leaves were fixed and further processed. Leaf tissue of ZYMV-XJ-infected pumpkin was harvested for virus purification. The purification procedure involved grinding tissue in high-salt buffer, precipitating the virus and isolating viral zones after density gradient centrifugation. Virus concentrations were determined using an estimated extinction coefficient 2.5. Green peach aphids (Myzus persicae) were used to transmit ZYMV-XJ; pumpkin was used as both donor and test plant. 1500 seeds from watermelon, muskmelon and pumpkin plants that had been naturally infected with ZYMV-XJ were planted in the greenhouse, and the existence of ZYMV-XJ in the seedlings was confirmed by testing seedlings with ELISA. Antisera to the Italian isolate ZYMV-It, French isolate ZYMV-Fr and antisera to WMV-l, WMV-2, PVY and TuMV were used for double-diffusion tests and ELISA. Antisera to ZYMV-XJ were prepared by injecting New Zealand white rabbits with purified virus.

Results and conclusions
ZYMV-XJ infected 12 plant species belonging to five different families, but caused severe systemic diseases only on some cucurbits. ZYMV-XJ only caused local chlorotic lesions on Chenopodium amaranticolor and C. quinoa. Long, flexuous, rod-shaped virus particles were observed in electron micrographs of leaf dips, and the modal length of the particles was close to 750 nm. Inclusion bodies consisting of pinwheels and scrolls were detectable in the ultra-thin section of ZYMV-XJ-infected tissue. The purified virus had an ultraviolet absorption profile typical of a nucleoprotein, with minima and maxima at 248 and 260 nm, respectively. M. persicae transmitted the virus in a non-persistent manner. None of the seedlings tested for seed transmission gave a positive reaction. Z-XJ sap reacted only with ZYMV antisera but not with WMV-l, W-2, PVY and TuMV antisera. ZYMV-XJ antiserum reacted only with ZYMV-XJ sap but not with WMV-2 sap. On the basis of the results above, the virus was determined to be a member of the potyvirus group.

1. Lisa V, Lecoq H, 1984. Descriptions of Plant Viruses No. 282.
2. Lesemann BE, Makkouk KM, Koenig R, 1984. Phytopathol. Z. 108, 304-313.