Cucurbit chlorotic yellows virus: a new Crinivirus of cucurbits spreading in Asia
In 2004, severe leaf yellowing symptoms were observed on glasshouse melons (Cucumis melo) in Kumamoto Prefecture (Kyushu), in the Southwest of Japan. Similar symptoms were observed in cucumber (Cucumis sativus) and watermelon (Citrullus lanatus). At approximately the same time, a pyrethroid-resistant strain of Bemisia tabaci (Hemiptera: Aleyrodidae – EPPO A2 List) emerged in that area, and was identified as biotype Q. Studies showed that the causal agent was a new virus, tentatively called Cucurbit chlorotic yellows virus (CCYV). This virus is transmitted by B. tabaci (biotypes B and Q). Inoculation experiments with whitefly vectors showed that all tested Cucumis species (except C. anguria and C. zeyheri) could be infected by CCYV. It was also found that Citrullus lanatus, Cucurbita pepo, and Luffa cylindrica were susceptible to the virus, although infection rates were low and symptoms unclear. In addition to cucurbits, other herbaceous plants could be systemically infected by CCYV during these experiments (Beta vulgaris, Chenopodium amaranticolor, C. quinoa, Spinacia oleracea, Lactuca sativa, and Nicotiana benthamiana). The complete genome of CCYV was sequenced and indicated that CCYV should be classified as a new and distinct Crinivirus species. It is also noted that CCYV-affected areas are increasing rapidly throughout Japan, most probably with the spread of B. tabaci biotype Q. After this initial discovery in Japan, CCYV was also detected on several cucurbit crops in China in 2008, and in Taiwan in 2009 (Okuda et al., 2010).
In China, systemic foliar chlorosis of melon, watermelon, and cucumber plants grown in plastic houses was first observed in Shanghai in 2008. By the end of October 2009, the disease had become prevalent across 13;000 ha of plastic houses in Shanghai, Ningbo (Zheijiang province) and Shouguang (Shandong province). It is estimated that crop losses ranged from 10 to 20%. Diseased crops were also infested by B. tabaci. Molecular studies confirmed presence of CCYV (Gu et al., 2011).
In Taiwan, CCYV was reported for the first time in 2009. In April 2009, symptoms of chlorosis, yellows, and bleaching accompanied with green veins and brittleness were observed on the lower leaves of melons (Cucumis melo) in Lunbei (Yunlin county). Similar symptoms were also observed on cucumber (Cucumis sativus), pumpkin (Cucurbita moschata), watermelon (Citrullus lanatus), bottle gourd (Lagenaria siceraria) and local types of melons planted in other areas of Yunlin and Changhua counties (Central Taiwan). Large populations of B. tabaci were observed in association with the diseased cucurbit crops, and were identified as biotype B. Molecular studies confirmed the presence of CCYV (Huang et al., 2010).
Pictures of CCYV symptoms can be viewed on the Internet:
Gu Q, Liu Y, Wang Y, Huangu W, Gu H, Xu L song F, Brown JK (2011) First report of Cucurbit chlorotic yellows virus in cucumber, melon and watermelon in China. Plant Disease 95(1), p 73.
Huang LH, Tseng HH, Li JT, Chen TC (2010) First report of Cucurbit chlorotic yellows virus infecting cucurbits in Taiwan. Plant Disease 94(9), p 1168.
Okuda M, Okazaki S, Yamasaki S, Okuda S, Sugiyama M (2010) Host range and complete genome sequence of Cucurbit chlorotic yellows virus, a new member of the genus Crinivirus. Phytopathology 100(6), 560-566.