The Asian Vegetable Research and Development Center (AVRDC), Shanhua, Tainan 741, Taiwan, Republic of China
USDA-ARS, Salinas, California
Pronounced yellowing symptoms on the lower leaves of tomato plants, similar to those caused by nitrogen deficiency, were observed in the spring of 1998 in The Asian Vegetable Research and Development Center and in farmers' fields in southern Taiwan. However, the brittleness of the discolored leaves, occasional upward leaf rolling, and abundance of whiteflies on these plants suggested the involvement of Tomato chlorosis virus (ToCV) and Tomato infectious chlorosis virus (TICV) that belong to the group of whitefly-transmitted, phloem-limited criniviruses (family Closteroviridae). Leaves of symptomatic and healthy plants were collected, and total nucleic acids were extracted from 0.2 g of leaf tissue (1). The total nucleic acids were precipitated by ethanol and dissolved in 160 μl of sterile water. Eight microliters of total nucleic acids were observed on positively charged nylon membranes (Roche Diagnostic GmbH, Roch Applied Science, Germany). Two digoxigenin-labeled riboprobes, transcribed from pTIC8-44 (complementary to the 3′-end region of TICV RNA 1) and pToC 78 (corresponding to the coat protein region of ToCV RNA 2), were used in hybridization tests to detect TICV and ToCV, respectively (2). Six of seventeen symptomatic tomato plant samples were positive with the ToCV probe, whereas none of the 13 samples reacted with the TICV probe. Similar symptoms as described above for tomato were observed on zinnia plants in the same locations. Five of eight zinnia samples gave a positive reaction with the ToCV probe. One of the ToCV positive samples also gave a positive reaction with the TICV probe. Electron microscopic examination from leaf-dip preparations of ToCV-positive leaf tissues, stained in 1% uranyl acetate, showed the presence of flexuous filamentous particles approximately 800 to 850 nm long. To our knowledge, this is the first evidence of the presence of ToCV and TICV in zinnia and ToCV in tomato in Taiwan.
References: (1) A. Hadidi et al. J. Virol. Methods 30:261, 1990. (2) G. C. Wisler et al. Phytopathology 88:402, 1998.