First finding of Freesia mosaic virus infecting freesia in India

Abstract

Freesias are popular garden plants in the family Iridaceae. Freesia spp. have been reported to be infected by various viruses: Bean yellow mosaic virus , Freesia mosaic virus , Cucumber mosaic virus , Tobacco rattle virus (Brunt, 1995) and ophioviruses (Vaira et al ., 2006). In April 2007, leaf samples showing chlorotic streaks were collected from Kangra region of Northern India. These samples were tested for the presence of potyviruses using an indirect ELISA kit (Agdia) as per the manufacturer’s instructions. A positive result was obtained from one of the ten collected samples. Total RNA was extracted from this positive leaf sample using RNAqueous® RNA isolation kit (Ambion). RT-PCR was performed with a degenerate potyvirus primer pair (P9502 & CPUP), which amplifies the partial coat protein (CP) gene and 3 ′ -UTR region of the viral genome (Van der Vlugt et al ., 1999). An amplicon of ~650 bp was obtained, which was cloned into pGEM®-T Easy vector (Promega) and sequenced. Analysis showed that the sequence shared 98% identity with the only sequence of the tentativelynamed Spiranthes mosaic virus 2 (SpMV2; GenBank Accession No. AY685219), reported from Spiranthes cernua in USA (Guaragna et al ., 2006). In order to sequence the full CP gene, primers were designed using the available SpMV2 sequence. The complete CP gene and 3 ′ -UTR was amplified, cloned and sequenced. A sequence of 1026 bp was submitted to the EMBL Database (Accession No. AM748701). This sequence showed 97% identity with a partial sequence (429 bp) of Freesia mosaic virus (FreMV; EF203688) obtained from a Dutch Freesia isolate, this short sequence is the only one available for FreMV. The Indian isolate showed less than 86% homology at the amino acid level with any other potyvirus. A host range study using the Indian isolate was carried out using Freesia and Spiranthes spp. The isolate could not be transmitted to the orchid; but it did infect Freesia , showing mild chlorotic symptoms, typical of FreMV infection. Based on the biological and sequence data, the present isolate has been identified as FreMV. This study also supports the case that SpMV2 is in fact an isolate/strain of FreMV, rather than being a distinct virus. This is the first report of FreMV in India.