Dolichos yellow mosaic virus from South India: Genetic characterization and evidence for recombination

Abstract

The field survey was made in the Dolichos growing areas of Coimbatore district in Tamil Nadu and disease incidence was ranged from 86-90%. The symptoms observed are golden yellow specks sparsely distributed in leaf lamina; in severe case the entire leaf lamina become yellow and yellowing of pods. The viral genome was cloned using rolling circle amplification and sequenced. The sequence analysis revealed that Dolichos yellow mosaic virus (DoYMV) is causing the yellow mosaic disease in Dolichos. DoYMV-CBE1 showed 99% identity with DoYMV -Mysore (AJ968370) while DoYMV-CBE2 shared 100% identity with DoYMV-Bang1 (AM157412) and DoYMV-Bang2 (AM157413). The phylogenetic dendrogram showed the DoYMV is distinct from other legume yellow mosaic viruses. One additional N-glycosylation site (NLTH, coordinates 101-104) was identified in the coat protein of DoYMV. Statistically significant recombination events were detected in the replication enhancer protein and transcription activation protein. The genomic components were exchanged from Croton yellow vein mosaic virus and Velvet bean severe mosaic virus to DoYMV. From the results it is inferred that DoYMV is genetically different from other yellow mosaic viruses. The yellow discolouration of pods and seeds of infected plants were suggestive that the virus may be seed borne, which was investigated in the present study. The distribution of virus in various parts of the seeds of Dolichos plants naturally infected in the field was determined by polymerase chain reaction and sequencing. Nucleotide sequencing of the PCR amplicons from the seed parts revealed the presence of Dolichos yellow mosaic virus (DoYMV) in the embryonic axes of the seeds analyzed. The virus detected in embryonic axes of infected Dolichos seed revealed that DoYMV is seed borne in nature.