The in vitro genebank of the International Potato Center (CIP) holds 4,486 accessions of potato, 5,574 sweetpotato, and 1,431 Andean roots and tuber crops (ARTCs). Currently, 67% of the in vitro potato accessions and 64% sweetpotato accessions are bacterial and fungal contaminants and are certified as virus-free. While the important diseases and their detection methods are well established for potato and sweetpotato, the ARTC’s have little information on diseases which infects them. Current research has begun to find efficient methods for diagnosing viruses in ARTCs.
CIP’s virus elimination procedure was originally developed inhouse with help from collaborators and has continuously evolved into an effective but relatively slow, low throughput process that never-the-less can be applied to a wide range of accessions and types of virus. Starting in 2008, methodologies for producing pathogen-tested free materials were improved and certified by the International Standard ISO/IEC 17025:2005.
The virus elimination process for potato and sweetpotato includes the following steps: (a) Initial health status testing by serological, molecular, and bioindexing (5 months); (b) Accessions found to be infected with viruses are subjected to thermotherapy (incubation of in vitro plants at 32-34 for potato and 35-37ºC for sweetpotato (~1 month), followed by meristem isolation (0.2-0.35mm meristems), and complete plant recovery (2-6 months); (c) Final health status testing (step a) is repeated to confirm that the resulting plants are virus-free ( ~ 5 months) .
Excision of potato meristems after undergoing 30 days thermotherapy (32-34ºC).
Detection Method *
Potato virus T
Potato spindle tuber viroid
Potato virus X
Potato virus Y
Potato leaf roll virus
Potato virus S
Andean potato mottle virus
Andean potato latent virus
Potato yellowing virus
Arracacha virus B- Oca strain
Sweet potato feathery mottle virus
Sweet potato mild mottle virus
Sweet potato caulimo-like virus
Sweet potato chlorotic fleck virus
Sweet potato C6 virus
Sweet potato mild speckling virus
Sweet potato chlorotic stunt virus
Sweet potato latent virus
Cucumber mosaic virus
Sweet potato virus G
* NASH: Nucleic Acid Hybrisation detection, DAS-ELISA: double-antibody sandwich method of the enzyme-linked immunosorbent assay, NCM-ELISA: immuno-enzymatic test that uses nitrocellulose membranes.
Bacterial contamination is only an issue for sweetpotato germplasm with about ~3% (182 accessions) of the collection infected. The bacterial contamination in sweetpotato appears to be endogenous and involves a suite of bacteria. Infection seems to be connected to the origin of the host plant as virtually all sweetpotato derived from African countries contain some type of bacterial infection. Although it is intriguing to speculate a beneficial effect of such endogenous bacteria in sweetpotato, no evidence of any beneficial effect has been reported. In potato, the incidence of bacterial contamination is less than 1% and therefore is a minor issue.
Bacteria cleaning: (A) Plants with bacteria (Note red coloration at medium surface (arrow). (B) Bacteria free plants.