Emergence of croton yellow vein mosaic virus in turnip (Brassica rapa subsp. rapa) indicated new host adaptation by a weed-infecting begomovirus

Turnip (Brassica rapa sub sp. rapa) germplasm accessions exhibiting severe leaf curl and stunting symptoms under natural field conditions were evaluated for the presence of begomovirus by PCR using a set of primers specific to begomoviruses. Two germplasm accessions, IC732033 and EC732034 were positive. Furthermore, detailed characterization of the begomovirus from the leaf curl-affected turnip plant (IC732033) revealed an association of croton yellow vein mosaic virus (CYVMV) and croton yellow vein mosaic betasatellite (CroYVMB). Agroinoculation of CYVMV construct alone or in combination with CroYVMB and back inoculation of the progeny virus from agroinoculated plants through whiteflies to healthy plants produced typical disease symptoms. Thus this study provides etiological evidence for the cause of leaf curl disease in turnip plants through the establishment of Koch’s postulates, similar to our earlier findings of CYVMV infection in rapeseed-mustard and crambe. Therefore, the present and past studies have shown that CYVMV, a weed-infecting begomovirus, outreaches Brassica crops, which were hitherto not known to be affected by a begomovirus.