In vitro virus elimination in three Andean root crops: oca (Oxalis tuberosa), ulluco (Ullucus tuberosus), and arracacha (Arracacia xanthorrhiza)

Accessions of three Andean root crops-oca (Oxalis tuber osa Molina), ulluco (Ullucus tuberosus Caldas), and arracacha (Arracacia xanthorrhiza Bancr.) were imported into quarantine in New Zealand. Using nitrocellulose membrane -ELISA, herbaceous hosts, and electron microscopy, the accessions were foun d to be infected with the following viruses. In oca: Arracacha vials B (AVB ), Papaya mosaic vii us (PapMV), and Ullucus mild mottle virus (UMMV); in u lluco: Ullucus virus C (UVC), Ullucus mosaic virus (UMV), PapMV, and UMMV; and in arracacha: Arracacha A virus (AVA). To comply with quarantine requir ements the viruses had to be eliminated. Except with one accession of oca t hat was infected with TMV/U, this was successfully achieved using a protoco l of in vitro virus elimination that combined heat and chemical therapy. St em nodal sections of oca and ulluco and shoot tips of arracacha were establ ished in tissue culture on a growth medium containing 50 mg/litre ribavirin . These explants underwent 10 days of continuous heat therapy of alternatin g 4 h light at 35 degreesC: 4 h dark at 31 degreesC, after which time the r esultant shoots were 1 cm long and ready to be excised and grown up on grow th medium without ribavirin. They were grown under normal tissue culture co nditions of 24 degreesC under fluorescent lights with a photoperiod of 16 h . The plantlets were then introduced to glasshouse conditions in preparatio n for field trials, analyses, and evaluations.