Development of an RT-PCR for High Plains virus indexing scheme in New Zealand post-entry quarantine

High Plains virus (HPV) causes a potentially serious economic disease of cereals and is of quarantine importance for New Zealand. HPV is transmitted by the wheat curl mite Aceria tosichella, and neither the virus nor its vector is present in New Zealand. Cereal seeds imported to New Zealand are required to be certified HPV-free, as the virus is a regulated pest. A procedure was developed for inspecting plants and testing cereal seedlings in quarantine using reverse transcriptase polymerase chain reaction (RT-PCR) as a detection method. A sample of 50,655 sweet corn seeds was taken from an imported commercial line and germinated in containment. Symptomatic seedlings were collected at 3 and 4 1/2 weeks after sowing. Eight out of 27 symptomatic samples tested HPV positive by RT-PCR and were confirmed by enzyme-linked immunosorbent assay (ELISA). Sequence analysis revealed that the HPV isolates had a 99.3 to 100% nucleotide identity and 99.0 to 100% amino acid similarity with the HPV USA isolate (GenBank accession no. U60141). HPV variants were detected by single stranded conformational polymorphism (SSCP) analysis but not by restriction fragment length polymorphism (RFLP).