A new begomovirus associated with yellow mosaic disease of Clerodendron

Clerodendron inerme (family Verbenaceae) is a common hedge plant in the gardens of India. In recent years, large numbers of plants have been exhibiting yellow mosaic symptoms. Typical symptoms are bright yellow spots along the midrib which coalesce to give a mosaic, a reduction in leaf size and stunting of the plant. Leaves with symptoms and apparently without symptoms were tested for virus infection by electron microscopy (EM), Southern hybridisation and polymerase chain reaction (PCR)-mediated amplification. No characteristic virus particles were detected by EM.

Figure 2: Agarose gel electrophoresis of ~750bp amplicon obtained with DNA extracted from infected leaves of Clerodendron spp.

Total DNA extracted from 15 symptomatic samples showed positive hybridisation to a radioactively-labeled Tomato Leaf Curl New Delhi Virus-[Potato] (ToLCNDV-[Pot], [AY286316]; Usharani et al., 2004) DNA A probe; indicating the presence of a begomovirus. No hybridisation was detected to samples extracted from plants without symptoms. PCR amplification with primers designed to the coat protein of ToLCNDV-[Pot] (PotAF 5' GTGAAGCGACCAGCAGAT 3'; PotAR 5' TTAATTTGTTACCGA ATCATA 3') yielded an approximately 750bp amplicon. The PCR product was cloned and sequenced (accession no. AY950580). Comparison with sequences of other begomoviruses showed the virus isolate under study to be most similar (80% nucleotide sequence identity) to Cotton Leaf Curl Kokhran Virus (AY456683). Lower levels of identity (<78%) were detected to other begomoviruses, including ToLCNDV. Since the CP is highly conserved amongst begomoviruses, the low levels of sequence identity may indicate that the virus associated with yellow mosaic disease of Clerodendron is a previously unidentified begomovirus.