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A Novel Geminivirus of Ipomoea indica (Convolvulacae) from Southern Spain

A cutting of Ipomoea indica displaying yellow vein symptoms was collected from Nerja in southern Spain in 1995, rooted, and maintained by vegetative propagation under glasshouse conditions at the John Innes Centre, Norwich. Although this member of the Convolvulaceae is native to the New World, it has escaped from cultivation as an ornamental and has now been naturalized in many tropical and warm temperate regions of the world, such as southern Spain. The same plant was found to host a population of whiteflies that were also brought back to containment facilities, and maintained in colony. Total plant DNA was extracted from the I. indica plant and universal primers for begomovirus A component (1) were used to amplify an approximately 2.8-kb fragment that was cloned and sequenced. The sequence is available in the DDJB, EMBL, and GenBank nucleotide sequence data bases under accession number AJ132548. A GENEMBL search with the complete sequence of the clone showed 70.8% identity to the AC1 gene of Ageratum yellow vein virus (AYVV). A search with the coat protein gene sequence showed highest homology to tomato leaf curl virus from southern India, another monopartite virus. Typical geminivirus vein yellowing symptoms, nucleotide sequence similarity, and EM detection of geminate virus particles strongly suggest that a geminivirus is present in this plant. The low level of homology to other sequenced geminiviruses suggests that it is an uncharacterized Begomovirus sp. With degenerate DNA-B primers (2), no B component has so far been detected. This virus is provisionally named Ipomoea yellow vein virus (IYVV). With techniques already established for identifying Bemisia spp. (3), the whiteflies collected with this Ipomoea plant were confirmed as Bemisia tabaci. Transmission studies to healthy I. indica showed that this whitefly population (named biotype S), the Q biotype from Spain, and the B biotype from Israel were all unable to transmit IYVV to healthy I. indica, tobacco, tomato, or nightshade. This may be due to many years of vegetative propagation of the host plant as an ornamental, resulting in loss of virus transmissibility by insects, which has occurred with Abutilon mosaic virus (AbMV) and honeysuckle yellow vein mosaic virus (HYVMV). This is the first report of a novel geminivirus on I. indica. It highlights the importance of weeds as hosts and potential reservoirs of both viruses and pests. We acknowledge support from the British Council, The Royal Society, BBSRC, and MAFF.

References: (1) R.W. Briddon and P. G. Markham. Mol. Biotechnol. 1:202, 1994. (2) M. R. Rojas et al. Plant Dis. 77:340, 1993. (3) R. C. Rosell et al. Ann. Entomol. Soc. Am. 90:575, 1997.