Alternanthera yellow vein virus (AYVV); a betasatellite independent begomovirus infecting Sonchus palustris in Pakistan.

Satellites associated begomoviruses are the most diverse group of plant viruses in tropical and subtropical regions. In Pakistan, during field surveys in 2019-2020, Sonchus palustris (a weed plant) was observed showing begomovirus symptoms i.e., vein yellowing and mosaic patterns on leaves. Rolling circle amplification from total isolated DNA of symptomatic leaves was performed to amplify circular viral genomes. Subsequent cloning and sequencing showed that a new strain of Alternanthera yellow vein virus (AlYVV) is associated with vein yellowing disease of S. palustris. The identity percentage analysis through BLAST search and SDT analysis showed that the new strain is 94-98% identical to AlYVV isolates reported from Pakistan, India and China. In phylogenetic tree, it clustered with AlYVV-[PK:E prostrata:15-KX710155], AlYVV-[PK:E prostrata:13]-KX906697] and AlYVV-[PK:E prostrata:11]-KX906694] previously reported from Pakistan. There was no detectable level of betasatellite or any other satellite molecule in the samples studied here. Phylogenetic analysis of Rep and CP genes of AlYVV with corresponding genes of closely related viruses circulating in Southeast Asia showed intra-specific recombination involving both complementary and virion sense region of virus. Relaxed clock and Bayesian Skyline Plot analysis based on CP gene sequences indicated slight higher substitution rates (4.75 x 10-3 substitutions/nucleotide/year). In the Indian subcontinent satellite-associated monopartite begomoviruses predominately infect crops and non-crop plants. But AlYVV is found infecting mostly non-crop plants independent of satellite molecules. We hypothesize here that AlYVV evolved as a true monopartite begomovirus in the Indian sub-continent and could be a great threat to introduced crops under suitable conditions. Such studies are crucial to understand probable future epidemics of begomoviruses in the region.