A novel group of asymptomatic potexviruses lacking a TGB3 gene and associated to mixed infections in Cassava (Manihot esculenta Crantz)
W. CUELLAR (1), I. Lozano (2), M. Cuervo (2), A. Leiva (2), M. Carvajal-Yepes (2) (1) International center for tropical agriculture, Colombia; (2) International center for tropical agriculture, Colombia

Several potexviruses (Family Alphaflexiviridae) have been reported to infect cassava (Manihot esculenta Crantz) in the Americas, the center of origin and domestication of the crop. Some of these viruses were first described 30–40 years ago isolated from severely diseased plants and include Cassava Caribbean mosaic virus (CsCaMV), Cassava Colombian symptomless virus (CsCSV), Cassava common mosaic virus (CsCMV), Cassava virus X (CsVX) and Cassava new alphaflexivirus (CsNAV). However, their definitive classification as distinct species remains unresolved for several reasons, including the lack of sequence data, affecting disease diagnostics, cassava germplasm exchange certification and epidemiological studies. Using virus indexing data from an in vitro and field collections of over 2000 cassava samples we obtained 3 major phylogenetic groups of potexviruses, one corresponding to isolates that reacted to antisera against CsCMV and other which reacted against CsVX antisera. Still one more group was detected that did not reacted against either antisera. These latter isolates grouped separately with CsNAV a recently reported potexvirus found in mixed infections in cassava. Further biological and genome analysis established that CsNAV and CsVX are readily distinguishable from CsCMV in that they cause latent single-infections in different cassava landraces and lack the gene 3 of the conserved potexviral ‘triple gene block’ (TGB). Neither CsNAV nor CsVX could be efficiently mechanically transmitted to indicator plants. In contrast, all CsCMV isolates caused Cassava Common Mosaic Disease (CCMD) in single infections. This is the first report of potexviruses found in natural infections and lacking a TGB3 gene. 

Abstract Number: P3-68
Session Type: Poster