Natural occurrence of a begomovirus on Pigeonpea in India

Pigeonpea (Cajanus cajan.; family Fabaceae) is an important pulse crop in India, Nepal, Bangladesh, Sri Lanka, Thailand and Myanmar for dietary protein requirements. The disease occurs in most pigeonpea-growing areas at a low incidence. Symptoms of the disease consist of yellow mosaic, mottling, shortening of leaves and stunting. The association of a geminivirus with the disease was suspected due to the presence of the whitefly Bemisia tabaci on the plants. In transmission tests B. tabaci successfully transmitted the disease from infected plants to pigeonpea seedlings, inducing typical disease symptoms. Mechanical inoculations failed to transmit the disease to pigeonpea.

To confirm the association of begomovirus with the disease, polymerase chain reaction (PCR) was performed using total DNA isolated from infected plants and two pairs of broad-spectrum begomovirus-detecting primers (Deng et al., 1994; Hallan, 1998). The PCR products obtained were analysed by agarose gel electrophoresis. Amplicons of the expected size (~500 bp and ~800 bp respectively) were produced from samples with symptoms, but not those without. In Southern hybridisation experiments, with a probe generated from the cloned coat protein region of the begomovirus Tomato leaf curl New Delhi virus (ToLCNDV; Hallan, 1998), the PCR products hybridised strongly under high stringency washing conditions.

The PCR product obtained using the Hallan primers was sequenced (Acc. No. AY927997). In alignments, the highest nucleotide sequence identities (95-97%) were with ToLCNDV-[Solanum] (AJ620187); a ToLCNDV isolated from Luffa (AY309957); ToLCNDV-Mild (U15016); ToLCNDV-[Lucknow] (Y16421); Pumpkin yellow vein mosaic virus (AY184487); and Cucurbita maxima yellow mosaic virus (AY396151). Based on these findings the virus associated with the disease was tentatively identified as an isolate of ToLCNDV. This is the first report of the occurrence of a begomovirus on pigeonpea from India.