P. Sreenivasulu

Development of recombinant coat protein antibody based IC-RT-PCR for detection and discrimination of sugarcane streak mosaic virus isolates from Southern India.

Summary. Sugarcane streak mosaic virus (SCSMV), causes mosaic disease of sugarcane and is thought to belong to a new undescribed genus in the family Potyviridae. The coat protein (CP) gene from the Andhra Pradesh (AP) isolate of SCSMV (SCSMV-AP) was cloned and expressed in Escherichia coli. The recombinant coat protein was used to raise high quality antiserum. The CP antiserum was used to develop an immunocapture reverse transcription-polymerase chain reaction (IC-RT-PCR) based assay for the detection and discrimination of SCSMV isolates in South India. The sequence of the cloned PCR products encoding 3′untranslated region (UTR) and CP regions of the virus isolates from three different locations in South India viz. Tanuku (Coastal Andhra Pradesh), Coimbatore (Tamil Nadu) and Hospet (Karnataka) was compared with that of SCSMV-AP. The analysis showed that they share 89.4, 89.5 and 90% identity respectively at the nucleotide level. This suggests that the isolates causing mosaic disease of sugarcane in South India are indeed strains of SCSMV. In addition, the sensitivity of the IC-RT-PCR was compared with direct antigen coating-enzyme linked immunosorbent assay (DAC-ELISA) and dot-blot immunobinding assays and was found to be more sensitive and hence could be used to detect the presence of virus in sugarcane breeding, germplasm centres and in quarantine programs.

Molecular characterization and interviral relationships of a flexuous filamentous virus causing mosaic disease of sugarcane (Saccharum officinarum L.) in India.

SummaryA virus isolate causing mosaic disease of commercial sugarcane was purified to homogeneity. Electron microscopy revealed flexuous filamentous virus particles of ca 890 × 15 nm. The virus isolate reacted positively with heterologous antiserum to narcissus latent virus form UK, but failed to react with potyvirus group specific antiserum. N-terminal sequencing of the intact coat protein (CP) and the tryptic peptides indicated that the virus was probably a potyvirus but distinct from several reported potyviruses. Comparison of the 3′-terminal 1084 nucleotide sequence of the RNA genome of this virus revealed 93.6% sequence identity in the coat protein coding region with the recently described sugarcane streak mosaic virus (Pakistani isolate). The molecular weight of the coat protein (40 kDa) was higher than that deduced from the amino acid sequence (34 kDa). The apparent increase in size was shown to be due to glycosylation of the coat protein which has not been reported thus far in the family, Potyviridae. This is the first report on the molecular characterization of a virus causing mosaic disease of sugarcane in India and the results demonstrate that the virus is a strain of sugarcane streak mosaic virus, a member of the Tritimovirus genus of the Potyviridae. We have named it sugarcane streak mosaic virus – Andhra Pradesh isolate (SCSMV-AP).

Taxonomic position of sugarcane streak mosaic virus in the family Potyviridae

Summary. A cDNA library was generated from purified RNA of sugarcane streak mosaic virus – Andhra Pradesh (SCSMV-AP). Two overlapping clones covering 3160 nucleotides encoding partial CI, complete 6K2, VPg-NIa and NIb genes were sequenced. A comparison of this sequence along with the 3′ terminal 1315 nucleotides of SCSMV-AP determined earlier with the other members of the family Potyviridae indicated that it had only 30% identity at the amino acid level for the partial polyprotein open reading frame (ORF) with the members of Ipomovirus and Tritimovirus genera. Further, in the most conserved NIb region also there was only 40% identity with the type members of these genera. Based on this analysis, we suggest the taxonomic affiliation of SCSMV-AP into an undescribed new genus in the family Potyviridae.

Tropical food legumes: virus diseases of economic importance and their control.

Diverse array of food legume crops (Fabaceae: Papilionoideae) have been adopted worldwide for their protein-rich seed. Choice of legumes and their importance vary in different parts of the world. The economically important legumes are severely affected by a range of virus diseases causing significant economic losses due to reduction in grain production, poor quality seed, and costs incurred in phytosanitation and disease control. The majority of the viruses infecting legumes are vectored by insects, and several of them are also seed transmitted, thus assuming importance in the quarantine and in the epidemiology. This review is focused on the economically important viruses of soybean, groundnut, common bean, cowpea, pigeonpea, mungbean, urdbean, chickpea, pea, faba bean, and lentil and begomovirus diseases of three minor tropical food legumes (hyacinth bean, horse gram, and lima bean). Aspects included are geographic distribution, impact on crop growth and yields, virus characteristics, diagnosis of causal viruses, disease epidemiology, and options for control. Effectiveness of selection and planting with virus-free seed, phytosanitation, manipulation of crop cultural and agronomic practices, control of virus vectors and host plant resistance, and potential of transgenic resistance for legume virus disease control are discussed.

Identification of a New Potyvirus Associated with Chlorotic Vein Banding Disease of Spathiphyllum spp., in Andhra Pradesh, India

The genome of a potyvirus isolate associated with chlorotic spots and vein banding symptoms on Spathiphyllum spp., in Andhra Pradesh state, India was amplified by RT-PCR using degenerate potyvirus primers, amplicons cloned, and sequence (1.6 kb) analyzed. This virus isolate shared maximum identity of 74.8% and 80.2% at coat protein (CP) gene nucleotide (906 nucleotides) and amino acid (302 amino acids) levels, respectively with Dasheen mosaic virus (DsMV)-M13 isolate reported from China. But its 3`-UTR (258 nucleotides) had maximum identity of 62.5% with DsMV-Vietnam isolate. The deduced molecular weight of CP is 33.57 kDa and it contained DAG triplet in its N-terminal region. In CP amino acid based phylogenetic analysis, this virus isolate represented a separate branch but closer to DsMV isolates cluster. Based on the molecular criteria set for the discrimination of species and genus in the Potyviridae family, the present virus isolate was identified as a distinct virus species in the genus Potyvirus and proposed the name Spathiphyllum chlorotic vein banding virus (SCVbV).

Sequence analysis of RNA3 of Maize stripe virus associated with stripe disease of sorghum (Sorghum bicolor) in India.

Maize stripe virus (MSpV), one of the distinct species of the genus Tenuivirus , has been associated with stripe disease of sorghum in India. In this study, we report the complete sequence analysis of ambisense RNA3 of four MSpV isolates associated with this disease, to confirm its correct identity. The RNA3 of four MSpV-Sorg isolates is 2357 nucleotides in length with two ORFs, one in virion sense (594 nucleotides, non-structural protein 3, NS3) and the other in complementary sense (951 nucleotides, coat protein, CP). The intergenic region between these two ORFs is 653 nucleotides in length, which is rich in U and A residues. The deduced molecular weights of NS3 and CP are ≈22 and ≈34 kDa, respectively. RNA3 has ≈82% sequence identity at nucleotide level with RNA3 of MSpV infecting maize in Florida, USA and Reunion. NS3 and CP ORFs shared ≈94% and ≈95% identities at amino acid levels, respectively with MSpV isolates of maize from Florida and Reunion. The internal non-coding region between two ORFs has 67–68% identity at nucleotide level with the reported MSpV isolates from Florida and Reunion. The sequence identity was more than ≈98% among the four isolates of MSpV-Sorg. Compared to maize-infecting MSpV isolates in USA and Reunion, the sorghum-infecting MSpV isolates in India had more amino acid substitutions in both NS3 and CP. This is the first report of complete sequence analysis of MSpV RNA3 from Asia.