Recombinant Tomato leaf curl New Delhi virus is associated with yellow vein mosaic disease of okra in India

Okra is the important vegetable crop grown across tropical and subtropical regions of the world. Yellow vein mosaic (YVMD) and enation leaf curl (ELCuD) diseases caused by begomoviruses are the major threat for cultivation and production of okra in India. Survey conducted between 2006 and 2010 revealed the incidence of begomovirus diseases ranged from 55 to 90% in okra growing states (ten states and two union territories) of the country. Three hundred forty-three okra leaf samples showing symptoms such as yellow mosaic, vein thickening, petiole bending, complete yellowing and upward leaf curling of leaves were collected from the surveyed locations across India. The PCR detection for begomovirus in the okra samples and subsequent cloning of partial genome sequencing of DNA A (1.2 kb fragment) indicated, 290 samples are associated with monopartite virus and 53 samples were associated with bipartite virus. Among the isolates showing highest identity with ToLCNDV, one isolate from each from five states was selected for amplification of full-length genomes (both DNA A and DNA B). The sequence analysis of DNA A and B components of five isolates revealed presence of nucleotide (nt) identity of > 90% with ToLCNDV infecting tomato, eggplant, and potato. Phylogenetic and recombination analysis indicated that both DNA A and DNA B components of ToLCNDV infecting okra has the recombinant origin from BYVMV, ToLCNDV, and SLCCNV as the foremost parents. Further, dot blot hybridization for detection of ToLCNDV was developed for using CP and NSP gene probe. This is the first report of ToLCNDV associated with yellow vein mosaic disease of okra in India.