Tomato spotted wilt virus (TSWV) infecting chrysanthemum (Dendranthema grandiflora L.) has been identified as a major constraint for chrysanthemum cut-flower industries in Southern India. The disease symptoms include veinal necrosis, necrotic spots on leaves, deformed flowers, and stem necrosis. The presence of TSWV in chrysanthemum plants collected from farms at Kotagiri, Nedugula, and Yercaud in Tamil Nadu State, India, was confirmed by the triple antibody sandwich-enzyme-linked immunosorbent assay (TAS-ELISA). The pathogenicity of TSWV was established for three isolates (TN1KO, TN2NE, and TN3YE) by mechanical inoculation of sap into chrysanthemum cuttings. Host range experiments in different host plants indicated that the isolates expressed symptoms typical of TSWV in all hosts assayed. Furthermore, Nicotiana tabacum L. had maximum virus titre among the tested host plants, and therefore was identified as the best indicator and the propagative host. The nucleocapsid (N) gene of the three studied isolates shared 99.2-100% identity at the amino acid level among themselves and 96.5-99.6% identity with reference TSWV isolates. The non-structural movement protein (NSm) gene of studied isolates shared 99.0% identity among themselves and 96.0%-100% identity at the amino acid level with reference TSWV isolates. The phylogenetic relationship analyzed based on the amino acid sequence identity of the N gene revealed that the studied isolate clustered as a single group with all the TSWV isolates taken for comparison. However, analysis based on the NSm gene indicated that the Indian isolates grouped with isolates from South Korea, the USA, Italy, Spain, and Australia.
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