First report of a begomovirus infecting Ocimum kilimandscharicum in India

Abstract

Ocimum kilimandscharicum, commonly known as Camphor basil, is a perennial evergreen shrub in the family Lamiaceae. Its essential oil possesses a wide range of pharmacological properties with anti-malarial, antioxidant, anti-microbial, and wound healing attributes (Soni et al., 2012). During a survey in February 2020, an infestation of whiteflies and viral symptoms, including leaf mottling, yellowing, mosaic, curling and deformation (Fig. 1), were observed on the leaves of O. kilimandscharicum in the experimental fields of the CSIR-Central Institute of Medicinal and Aromatic Plants, Lucknow, India. The disease was observed in patches of plants in different parts of the field (an area of c. 80 m2 in total) and disease incidence was estimated to be approximately 20%. The disease was not transmissible via mechanical inoculation with sap obtained from infected leaf tissues to O. kilimandscharicum, Nicotiana benthamiana or N. glutinosa. Eighteen samples (13 diseased and five asymptomatic) were collected from different locations of the field and total genomic DNA was isolated. PCR was done using begomovirus coat protein gene-specific primers (Hallan et al., 1998). All 13 diseased samples yielded an amplicon of c. 770 bp while no amplification was observed from the five asymptomatic samples. The positive samples were subjected to PCR using two sets of overlapping primers K1F/K1R and K2F/K2R for complete genomic characterisation of the DNA-A segment (Kumar et al., 2011). The samples yielded amplicons of c. 1,200 bp and 1,700 bp, respectively. The PCR products were cloned and sequenced. BlastN analysis revealed 97.6% identity with the DNA-A segment of Tomato leaf curl New Delhi virus (ToLCNDV) from lentil isolated in Kanpur, India (Naimuddin et al., 2016). The sequence was submitted to GenBank (Accession no. OP589304). Phylogenetic analysis was performed with different begomovirus isolates (Table 1) using MEGA 7 software (Tamura et al. 2004). The isolate in the current study and ToLCNDV ex lentil share a common ancestor and fall in the same clade (Fig. 2). Ongoing increases in the incidence of begomovirus infection in economically important crops are becoming a major concern globally. To the best of our knowledge this is the first record of a begomovirus infecting O. kilimandscharicum. Camphor basil is commonly grown in kitchen gardens and commercial fields, and infected plants may serve as a virus reservoir for other hosts, therefore, management strategies are required. We are thankful to the Director, CIMAP, Lucknow for the necessary facilities and DST-New Delhi for INSPIRE-SRF to Soumya Sinha.