September 26, 2003
From: British Society Plant Pathology, New Disease Reports, Vol 8: Aug 2003 - Jan 2004 [edited]

Potato leaf curl - a new disease of potato in northern India caused by a strain of Tomato leaf curl New Delhi virus
K. S. Usharania, Plant Virology Unit, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi 110012, India; B. Surendranatha (as for Usharania); S.M. Paul-Khurana, Central Potato Research Institute, Shimla, 171001, India; I.D. Garg, (as for Paul-Khurana); and V.G. Malathia (vgmalathi@rediffmail.com)
Accepted for publication 1 Sep 2003.

A severe leaf curl disease has been observed since 1999 in potato (_Solanum tuberosum_) crops in northern India. Affected plants were severely stunted with apical leaf curl, crinkled leaves, and expressed conspicuous mosaic. Garg et al. (2001), using polyclonal antiserum to Indian cassava mosaic virus in IEM, detected a begomovirus associated with this disease.

Inoculum from a severely affected potato plant was sap-transmitted to _Nicotiana benthamiana_ [Nb] seedlings, in which it induced severe leaf distortion and stunting 15 days post inoculation. Meristem-derived plantlets of potato cv. Kufri Anand inoculated with sap from infected Nb leaves developed yellow mottling, mosaic, and leaf curl symptoms.

Double-stranded viral replicative DNAs were purified from infected potato and Nb plants and cloned at HindIII, BamHI, XbaI, and PstI sites in the vector pUC18. The clones at the XbaI and PstI sites had a unit genome length insert (approx. 2.7 kb) which hybridized with the viral replicative forms from the infected plants. The nucleotide sequence of the XbaI and PstI clones corresponded to the DNA A (Accession No. AY286316) and B (Accession No. AY158080) components of the causal begomovirus.

Comparison of the complete nucleotide sequence of DNA A revealed that it has 93-95 percent identity with that of ToLCV-NDe isolates and <75 percent identity with other Tomato leaf curl virus isolates and Potato yellow mosaic virus.

A whitefly-transmitted potato begomovirus has not been reported previously in India, probably as potato crops on the North Indian plains have been cultivated during winter months, when whitefly populations are low. However, in recent years, potato crops have been planted earlier, resulting in a sufficient buildup of whitefly populations that might have led to the emergence of a new potato disease.

The nucleotide sequence data indicate that the cause is a virus closely related to ToLCV-NDe which, unlike the strain infecting potato, is not sap-transmissible and is not known to infect potato naturally. Therefore it is likely that a new strain of ToLCV-NDe has emerged that infects potato, a new host.

This is the first observation of a begomovirus causing a severe disease of potato in India. We conclude that potato leaf curl disease is caused by a strain of Tomato leaf curl New Delhi virus (ToLCV-NDe).

Reference:
Garg ID, Paul-Khurana SM, Kumar S, Lakra BS, 2001. Association of a geminivirus with potato apical leaf curl in India and its immuno-electron microscopic detection. Journal of Indian Potato Association 28, 227-232.