|Survey of diagnostic tools for detection of viroids and impacts of test results on the seed industry|
R. W. HAMMOND (1). (1) USDA ARS NEA MPPL, Beltsville, MD, U.S.A.
Viroids are unencapsidated, single-stranded, covalently closed circular, highly structured noncoding RNAs of 239 – 401 nucleotides that are replicated by host enzymes and cause disease in several economically important crop plants. Although viroids are primarily and easily transmitted mechanically through contact with contaminated pruning tools, by human hands, and by contact between plants, they are also spread vegetatively by graft inoculation, cuttings, micro-plants and tuber propagation, and in some cases, by insects. Pospiviroids (type member <i>Potato spindle tuber viroid</i>, PSTVd) are also transmitted through infected pollen and seed at variable rates, and seed transmission has recently been shown to contribute to the international interception of several pospiviroid species. Seed certification programs, which rely on sensitive diagnostic and detection methods and quarantine enforcement, have resulted in effective control of several diseases caused by viroids, eg. resulting in the eradication of PSTVd from potato in North America. This presentation will attempt to provide a critical examination of the evidence for seed transmission of viroids and its role in the epidemiology of pospiviroid infections in vegetable crops, methods used and limitations for detection of viroids in seeds, and implications for the seed industry and growers.