Zucchini Yellow Mosaic Virus Causes Begonia Chlorotic Ringspot in Chinese Taipei

Begonia plants (Begonia semperflorens Link & Otto) with chlorotic ringspot symptoms on the leaves were found in Taichung, Chinese Taipei. Isolation of the virus was conducted by single-lesion transfers on Chenopodium quinoa by mechanical inoculation. Chlorotic spots appeared 7-10 days after inoculation. Back inoculation with an isolated virus culture to virus-free begonia confirmed the pathogenicity of the virus to begonia. Electron microscopic examinations revealed flexuous rod-shaped virus particles of 750x13 nm in the crude sap from infected plants and purified virus preparations. Typical inclusion bodies of potyviruses were also observed in ultrathin sections of infected tissues from begonia, squash and C. quinoa. Serological tests, including indirect-ELISA and western blotting, indicated that the isolated virus was serologically related to Zucchini yellow mosaic virus (ZYMV). The virus caused local lesions on inoculated leaves of C. quinoa, systemic mosaic in cucumber (Cucumis sativus), zucchini (Cucurbita pepo) and Cucumis metuliferus, and chlorotic ringspots in begonia. The symptoms caused in cucurbits by the begonia isolate were much milder than those caused by ZYMVs of cucurbit origin. Complementary DNA fragments derived from viral genomic RNAs were cloned, sequenced, and the full-length sequence was submitted to the EMBL database (AM422386). The genomic RNA consists of 9591 nucleotides excluding the poly-A tail and contains an identical genome organization as those reported for members of the genus Potyvirus. The nucleotide sequence of the full-length genome and the deduced amino acid sequence of the coat protein share 98% identity to those of ZYMV-CU (AJ307036), ZYMV-SG (AJ316228), and ZYMV-TW-TN3 (AF127929). This is the first observation of natural ZYMV-infection in begonia.