June 2, 2005
Source: British Society for Plant Pathology, New Disease Reports, Vol. 11 [edited]

Natural occurrence of a begomovirus on Pigeonpea in India
S.K. Raj, M.S. Khan and R. Singh, Molecular Virology, National Botanical Research Institute, Lucknow-226 001, India. Accepted for publication 24 Feb 2005.

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_ [Bt] on the plants. In transmission tests, Bt successfully transmitted the virus 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, PCR was performed using total DNA isolated from infected plants and 2 pairs of broad-spectrum begomovirus-detecting primers (Deng et al., 1994; Hallan, 1998). The PCR products obtained were analyzed by agarose gel electrophoresis. Amplicons of the expected size (around 500 bp and 800 bp, respectively) were produced from samples with symptoms, but not from those without. In Southern hybridization 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 hybridized 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 percent) 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 1st report of the occurrence of a begomovirus on pigeonpea from India.

References

Deng D, McGrath PF, Robinson DJ, Harrison BD, 1994. Detection and differentiation of whitefly-transmitted geminiviruses in plants and vector insects by the polymerase chain reaction with degenerate primers. Annals of
Applied Biology 125, 327-336.

Hallan V, 1998. Genome organization of a geminivirus causing leaf curl in tomato (Lycopersicon esculentum). Lucknow, India: University of Lucknow, Ph.D thesis.

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[There are 7 ToLCNDV isolates that have been reported from India and 2 from Thailand. Recombination or pseudo-recombination are driving forces in the evolution of new begomoviruses, especially in tropical regions. Disease management of ToLCNDV depends in part on preventing movement of Bt-infested plants (e.g.. tomato transplants) to virus-free areas. Various control options include removal of infected plants (roguing), removal or burial of infected crop residues and intercropping in combination with chemical  insecticides and the use of available resistant cultivars. Use of plastic UV-absorbing screening material to exclude Bt is another method. Genetic resistance to begomoviruses has been reported in some wild _Lycopersicon_ species such as _L. hirsutum_ and _L. peruvianum_, which might be transferred to tomato. In Pakistan, resistance to leaf curl virus has been incorporated into tomato and chili cultivars.

Links:
<http://www.tropicalwhiteflyipmproject.cgiar.org/docs/brochure.pdf>
<http://www.tropicalwhiteflyipmproject.cgiar.org/docs/Tropical-Whitefly-IPM-Project-Brochure-2004.pdf>
<http://gemini.biosci.arizona.edu/viruses/tolcndv/>
<http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-41582002000500001&lng=en&nrm=iso>
- Mod.DH]