First report on the occurrence of Cucurbit aphid-borne yellows virus on nine cucurbitaceous species in China

In the late summer of 2006, viral symptoms were observed on cucurbitaceous field crops growing in many regions of China. These included yellowing (Fig. 1), sometimes combined with severe mosaic and in some cases, fruit malformation. The observed incidence of disease symptoms ranged from 30% to nearly 100%. Given the symptoms and the presence of large numbers of aphids, infection by Cucurbit aphid-borne yellows virus (CABYV; genus Polerovirus, family Luteoviridae) was suspected. CABYV is the first luteovirus reported that naturally infects cultivated cucurbits (Lecoq et al., 1992; D`Arcy et al., 2005).

A survey was carried out for CABYV using samples collected from 9 different cucurbit species: cushaw (Cucurbita moschata), squash (Cucurbita pepo), calabash gourd (Lagenaria siceraria), cucumber (Cucumis sativus), suakwa vegetable sponge (Luffa cylindrical), watermelon (Citrullus lanatus), muskmelon (Cucumis melo), wax gourd (Benincasa hispida) and bitter gourd (Momordica charantia); collected from selected fields in 10 different Provinces: Beijing, Shanghai, Zhejiang, Jiangsu, Henan, Liaoning, Shaanxi, Gansu, Inner Mongolia and Yunnan. Total RNA was extracted from fresh leaf samples and RT-PCR was performed as described by Han et al. (2000), using a primer set ( 5’- GAC TGC TCC GGT TTT GAC TGG - 3’ and 5’- CGT CTA CCT ATT TCG GGT - 3’) designed from a published CABYV sequence (Acc. No. NC003688; Guilley et al, 1994). In total 54 out of 111 samples tested positive, including samples taken from all ten Provinces and all nine curcucrbit species. Subsequently, representative RT-PCR products from 4 different cucurbit species were cloned and sequenced. The sequences obtained were submitted to GenBank (Acc. Nos DQ973124 from Squash; EF063705 from Cushaw; EF063706 from Cucumber and EF063707 from Suakwa vegetable sponge). Sequence analysis showed that these submitted sequences shared between 93.5–95.0% identity with a French isolate (CABYV-N; Acc. No. NC003688). In addition, spherical particles approximately 26 nm in diameter were also observed in some samples by electron microscopy.

These results demonstrate that CABYV occurs widely in China, being found on all the nine different cucurbitaceous species surveyed. To the best of our knowledge, this is the first report of the occurrence of CABYV in China.

Acknowledgments

This research was partially supported by a grant from the National Key Technologies R&D Program of China (2006CB101903).