Advanced Centre for Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi-110012, India.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
DNA beta molecule have been found associated with monopartite begomoviruses like Ageratum yellow vein virus, Cotton leaf curl virus and Tomato yellow leaf curl virus. In the year 2004, we reported (Sivalingam et al., 2004) for the first time association of DNA â molecule with a bipartite begomovirus, i.e., ToLCNDV. To determine the role of DNA â in ToLCNDV infection, infectious clones of the genomic components of ToLCNDV (DNA A and DNA B) and the associated DNA â were agroinoculated in various combinations to Nicotiana benthamiana and tomato cv. Pusa Ruby. DNAA alone ToLCNDV was found infectious in both the hosts, but the infected plants. developed very mild symptoms. The severity of symptoms was greater in plants inoculated with DNAA+â or DNAA+B. The plants inoculated by all the three components, developed most severe symptoms. In N. benthamiana, DNAA+B+â produced severe leaf curl symptoms; smaller leaves with downward curling. Similarly, DNA A+B+â inoculated tomato plants produced small leaves with curling and downward rolling symptoms in addition to typical leaf curl symptoms produced by DNA A+B inoculated plants. By Southern blot and PCR-titration, showed the amount of DNAA increase in the plants inoculated with DNA A+ B and the maximum increase was found in the plants inoculated with DNA A+B+â, suggesting that DNA â helps in rapid multiplication of DNA A component of the virus. Transmission by whitefly from plants infected with all the three components (DNA A, DNA B and DNA â) was better compared to plants infected with DNAA alone or DNA A+â or DNA A+B. DNA â did not influence the host range of ToLCNDV as all the host infected by DNA A+B were also infected with DNAA+B+â. ToLCNDV was transmitted from agroinoculated N. benthamiana with DNA A+B and DNA A+B+â to N. benthamiana and tomato by sap but not from DNA A and DNA A+â inoculated plants. The study demonstrated that in bipartite begomovirus DNA â is not essential for infection, but it increases disease severity, helps in viral DNA A accumulation and improves transmission efficiency by whitefly. It, however, does not facilitate the sap transmissibility and may not be involve in determining the host range of the virus.
