First report of a begomovirus infecting Calendula in India

Calendula officinalis (family Asteraceae) is grown as an annual ornamental plant in India for its beautiful flowers. Yellow vein net disease of Calendula was observed on several plants growing in gardens at Aligarh and Lucknow. Symptoms of the disease consist of vein yellowing, shortening of leaves and petioles, and stunting of plants. The disease was experimentally transmitted from naturally infected Calendula to healthy seedlings by whiteflies (Bemisia tabaci), but not by mechanical or aphid transmission.

Total DNA was extracted from leaves of plants with and without symptoms, and PCR was performed using a pair of primers designed to the coat protein region of a well characterised begomovirus, Tomato leaf curl New Delhi virus (ToLCNDV; Hallan, 1998). Agarose gel electrophoresis of PCR products showed amplification of a product of the expected size (~800 bp) from infected but not from healthy samples. The authenticity of PCR amplicon was further confirmed by cross hybridisation with a ToLCNDV DNA A probe. The PCR product was cloned and partially sequenced (Acc. No. AY887174). Sequence analysis revealed the highest nucleotide sequence identities (95%, 94% and 93%) of the virus infecting Calendula with Tobacco curly shoot virus (AF240675), Ageratum enation virus (AJ437618) and Tomato leaf curl Bangladesh virus (AF188481) respectively.

On the basis of whitefly transmission, amplification of an expected size DNA band with begomovirus detecting primers by PCR, positive hybridization of PCR products with a known begomovirus specific probe and its high sequence identity to known begomoviruses, the virus isolate under study was identified as a begomovirus. Yellow vein net disease of Calendula associated with Cucumber mosaic virus has been reported previously (Naqvi & Samed, 1985). However, this report is the first record of the natural infection of Calendula by a begomovirus.