Antigenic Diversity, Peptide Profiling and Coat Protein Sequencing Relationship of a Virus Isolate Causing Mosaic Disease of Sugarcane in Uttar Pradesh, India

Sugarcane mosaic potyvirus (SCMV) UP-isolate was antigenically similar to SCMV-A, SCMVMDB and two SCMV isolates from Thailand. The results were confirmed either by DAC-ELISA, EBIA, DIBA and ISEM independently or in combination. No reaction was evident with antiserum specific for other members of the Sugarcane mosaic potyvirus subgroup or any other potyviruses tested. The peptide profiling of a tryptic digest of the coat protein and amino acid sequencing of the coat protein of SCMV-UP isolate also revealed different patterns from those reported from other potyviruses infecting sugarcane. It appears likely that the severe mosaic observed on many varieties of sugarcane in Uttar Pradesh is caused by a pathotype of Sugarcane mosaic virus: , Introduction Results and discussion Sugarcane is extensively grown as a commercial The Uttar Pradesh Sugarcane mosaic virus crop in Uttar Pradesh and mosaic is very common. (SCMV-UP) isolate was antigenically similar to The virus isolates causing mosaic in Uttar Pradesh Sugarcane mosaic virus isolates A and MDB from have been recently partially characterised and classithe USA and two SCMV virus isolates from Thailand fied (Rao et al., 1998). To further characterise the (Table 1). The results were confirmed either by DAC virus causing this severe form of mosaic, peptide proELISA, EBIA, DIBA and ISEM independently or in filing and amino acid sequencing were conducted to combination. It was interesting that the SCMV UPprovide a basis to determine the antigenic relationisolate reacted strongly with the anti-Sugarcane ships between the virus isolates causing mosaic streak mosaic virus-Andhra Pradesh (SCSMV-AP) disease of sugarcane. antiserum in an ISEM test (data not shown). SCSMV, recently reported from South India, is reported to be a Materials and methods member of the genus Tritimovirus, in the family The virus isolate causing mosaic disease of sugarPotyviridae (Hema et al., 1999). No reaction was cane in Uttar Pradesh (Rao et al., 1998) was compared noticed with antisera prepared against MDMV-A, with 19 other potyviruses by Direct Antigen Coating SCMV-B, BC, -Sabi, -SC,I, -Yu, JGMV, SrMV-H (DAC)-ELISA (enzyme-linked immunosorbent and -I, CpABMV, SPFMV, HMV, EgMoV, or PVY assay), DIBA (dot immuno-binding assay), EBIA (Table 1). (electro-blot radioimmunoassay) and ISEM (immunoThe positive reactions between the UP isolate and sorbent electron microscopy). DAC-ELISA (Clark the SCMV isolates from USA and Thailand, and with and Bar-Joseph, 1984), Western blotting (O'Donnell the SCSMV-AP isolate may be due to the presence of et al., 1982) and ISEM (Milne and Lesemann, 1984) common epitopes in the coat protein (Shukla et al., were performed as described. Antigens for these tests 1994). The negative reaction of the UP isolate with were used only as virus-infected sap extracts. For antisera against MDMV-A, SCMV-B, MDB, BC DAC-ELISA 1:10, 1:100 and 1:1000 dilutions of Sabi, SC, I, Yu, JGMV, SrMV-H and -I. CpABMV, antigen, antiserum and anti-rabbit immunoglobulin SPFMV, HMV, EgMoV, PVY demonstrated that alkaline phosphatase conjugate were used, respecthere is variation in these isolates, presumably due to tively. For ISEM, the antiserum at 1: 1000 dilution was epitopic differences. Differences in biological, seroused for decoration of virus particles. logical and molecular properties between isolates of Peptide profiling studies of the coat protein of the SCMV from USA and Australia have been preSCMV-UP isolate were performed according to the viously reported (Tosic et al., 1990; Shukla et al., method of McKern et al. (1990). Peptide fragments 1994). HPLC peptide profiles of a tryptic digest of were subjected to vapour-phase hydrolysis at 110°C the coat protein of SCMV-UP isolate (data not in 5.8M HC1 containing 0.01% phenol for 20-22 h shown) indicated that this isolate could be differentiunder Nz. The fragments were then analysed on a ated from all the existing strains of sugarcane mosaic Water's amino acid analyser using an ion-exchange virus strains (McKern et al., 1991). The HPLC column as described by Badge et al. (1997). peptide profiles of SCMV-UP isolate had a greater