Is sweet potato leaf curl virus, a whitefly transmitted begomovirus, really seed transmitted?

Sweet potato leaf curl virus (SPLCV), a begomovirus (Geminiviridae) transmitted via vegetative propagation of sweetpotato or by the whitefly species Bemisia tabaci, threatens global sweetpotato production. Complicating management of SPLCV is the disputed publication of seed transmission of this begomovirus, a group of viruses which before 2015 were not reported to be seed transmissible. That report prompted an investigation into the validity of seed transmission of SPLCV. In this study, experiments were conducted on nearly 18,000 individuals. Conventional and quantitative real-time PCR were performed to detect the presence of virus on seed coats (seed-borne; contaminant) and in germinated seedlings. Virus was detected on seed coats in each year of the study. Year one, ca. 3,500 seedlings were tested, and no seed transmission was detected. Year two, ca. 13,500 seedlings derived from breeding seeds of SPLCV-infected plants were examined. Two bulked samples were positive for SPLCV; however, adult whiteflies were observed in the greenhouse, therefore transmission via the seed versus the vector could not be determined. Year three, 900 seedlings were grown, with no seed transmission detected. With the possibility of vector transmission in year two, whitefly transmission tests were conducted. Vector tests with viruliferous B. tabaci demonstrated successful transmission of SPLCV to seedlings. Successive years of repeated large-scale, multi-family grow-out experiments did not support seed transmissibility of SPLCV but highlighted strong potential for whitefly transmission.