Elimination and detection of viruses in meristem-derived plantlets of sweetpotato as a low-cost option toward commercialization

Viral diseases affecting sweetpotato are the most devastating and cause up to 98 % yield loss. In this paper, we report, meristem culture, graft transmission and virus indexing for management of viral pathogens in seven elite sweetpotato cultivars. Plantlets were developed in vitro from the apical meristematic dome with one to two leaf primordia. Mericlones were grafted on virus-sensitive indicator plant Ipomoea setosa and no viral disease symptoms were seen on I. setosa leaves in most cases. This indicates that no viruses translocated from meristem-derived scions to the virus-sensitive root stock. On the other hand, most of the non-tested traditional planting material induced distinct disease symptoms upon grafting, which revealed the presence of one or more viruses in it. About 85 % of mericlones recovered from 0.3-0.5 mm size meristem were tested as virus free, whereas it is difficult to culture meristems smaller than 0.3 mm due to dissection damage and too small a size. Virus-tested mericlones were further micropropagated and transferred to the field. Only few plants were found to be diseased in the R1 field trial. Root yield in the R2 generation was increased significantly when compared with non-tested control plants. During field exposure, only a low percentage of healthy plants were found infected with viruses when managed in a net house. This implies that viral vectors were present during the growing season and reinfection could be effectively reduced by net house management. We concluded that this low-cost technique of producing virus-tested planting material would significantly boost the yield through efficient removal of yield-reducing pathogens.