Potato leaf curl - a new disease of potato in northern India caused by a strain of Tomato leaf curl New Delhi virus

A severe leaf curl disease has been observed since 1999 in potato (Solanum tuberosum) crops in northern India. The affected plants were severely stunted with apical leaf curl and crinkled leaves and a conspicuous mosaic (Fig 1). Garg et al. (2001) showed that, using polyclonal antibodies to Indian cassava mosaic virus in immunospecific electron microscopy, a begomovirus was associated with this disease. We report here that the leaf curl disease in potato is caused by a strain of Tomato leaf curl New Delhi virus (ToLCNDV).

The begomovirus from a severely affected potato plant was sap transmitted to Nicotiana benthamiana seedlings in which it induced severe leaf distortion and stunting 15 days post inoculation (Fig 2). Meristem derived plantlets of potato cv. Kufri Anand inoculated with sap from infected N. benthamiana leaves developed yellow mottling, mosaic and leaf curl symptoms. Double stranded viral replicative DNAs were purified from infected potato and N. benthamiana 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 (~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 begomovirus causing the disease. Comparison of the complete nucleotide sequence of DNA A revealed that it has 93-95% identity with that of ToLCNDV isolates and <75% identity with other Tomato leaf curl virus isolates and Potato yellow mosaic virus. A whitefly transmitted begomovirus of potato 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 and this has resulted in a sufficient buildup of whitefly populations that might have led to the emergence of a new disease in potato.

This is the first observation of a begomovirus causing a severe disease of potato in India. The nucleotide sequence data indicate that the cause is a virus closely related to ToLCNDV 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 ToLCNDV has emerged that infects a new host, potato.