1Div. Plant Pathology, Sugarcane Res. Station, Kunraghat, Gorakhpur 273 008, India; 2Dept. Plant Pathology, Faculty of Agric., Univ. Belgrade, Yugoslavia; 3Dept. Crop Sciences, Univ. of Illinois, Urbana, IL 618011 USA; 4Div. Mycol. & Pl. Pathology, IARI, New Delhi 110 012, India; 5CSIRO, Div. Biomolecular Eng., 343 Royal Parade, Parkville, VIC 3052, Australia

Background and objectives
Recently, the taxonomy of sugarcane mosaic potyvirus subgroup was established by using cross-absorbed polyclonal antibodies directed towards the surface-located virus-specific amino termini of the coat proteins [1]. It is well known that the SCM potyvirus subgroup consists of four viruses: sugarcane mosaic virus I (SCMV), maize dwarf mosaic virus (MDMV), sorghum mosaic virus (SRMV) and Johnsongrass mosaic virus (JGMV). We found severe mosaic symptoms on sugarcane leaves having potyvirus-like particles, but these could not be detected by any of the antisera of SCM potyvirus subgroup and PVY. These results prompted us to characterise the virus on the basis of biological reactions on differential hosts and serology.

Materials and methods
The biological reactions on differential hosts were studied according to recent criteria developed by Tosic et al. [2]. However, for serological studies, immunosorbent electron microscopy and Western blotting techniques were used.

Results and conclusions
Severe mosaic symptoms were observed on leaves of sugarcane var. Cose 93232 in the vicinity of Gorakhpur, UP, India during crop seasons of 1995-96. The affected leaves showed a severe mosaic pattern with mosaic mottling. Virus was propagated and purified from sorghum leaves. Purified preparations contained a large number of filamentous flexuous particles of size 750 nm. Polyclonal antiserum with a titre of 1:1024 in DAC-ELISA test was produced in rabbit. So far four potyviruses were reported to cause mosaic symptoms on sugarcane throughout the world: sugarcane mosaic virus (SCMV), maize dwarf mosaic virus (MDMV), sorghum mosaic virus (SRMV) and Johnsongrass mosaic virus (JGMV). Since the particle morphology and size of the virus isolate could be compared with a potyvirus, the confirmation of its aetiology on the basis of serological relationships and biological reactions on differential hosts was studied with respect to members of sugarcane mosaic potyviruses. However, the virus under study could not be detected by any of the antisera used in the serological tests. The virus under study varied markedly with respect to reactions on differential hosts and serology (ISEM and Western blotting) from other members of sugarcane mosaic potyviruses reported to infect sugarcane naturally or artificially. Again the virus isolate also could not be recognised by PVY antiserum and vice versa during Western blotting. The virus was also found to be transmitted by aphids in a non-persistent manner. Our results suggest that it may be possible that this would be a new virus on sugarcane, which could only be confirmed after coat protein sequencing and nucleotide mapping which is in progress.

1. Shukia DD, Frenckel MJ, McKem NM et al., 1992. In Barnet OW (ed) (Arch. Virol. Suppl. 5), Springer Verlag, Wien, pp. 363-373.
2. Tosic M, Ford RE, Shukla DD, Jilka J, 1990. Plant Dis. 74, 549-552.