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item Boydston, Rick
item Mojtahedi, Hassan
item Thomas, Peter
item Anderson, Treva
item RIGA, E

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2003
Publication Date: 6/1/2004
Citation: Boydston, R.A., Mojtahedi, H., Crosslin, J.M., Thomas, P.E., Anderson, T.L., Riga, E. 2004. Evidence for the influence of weeds on corky ringspot persistence in alfalfa and scotch spearmint rotations. American Journal of Potato Research. 81:215-255.

Interpretive Summary: Corky ringspot (CRS) is a serious disease of potato caused by tobacco rattle virus (TRV) and vectored by stubby root nematods. CRS causes necrotic arcs, rings, or spots in potato tubers, which can result in crop rejection. The incidence of CRS in the Pacific Northwest (PNW) potato growing regions has increased since first reported in Washington State in 1976. Soil fumigation prior to planting potatoes is the only tool currently available to growers to control or suppress CRS in soils. We have demonstrated nematodes containing the TRV were no longer able to transmit the virus to susceptible plants after growing for several generations on alfalfa or Scotch spearmint, suggesting that CRS could be cleansed from fields by growing these rotation crops. However, weed hosts of TRV or stubby root nematode present in crop rotations could allow the disease to persist. Several weed host were identified that when present in cultures of alfalfa or scotch spearmint allowed CRS to persist. Hairy nightshade was a particularly good host of TRV and stubby root nematode. These results will allow growers to target control of known weed hosts in order to successfully eliminate CRS from fields using alfalfa and Scotch spearmint rotational crops.

Technical Abstract: Corky ringspot disease (CRS) in potato is caused by tobacco rattle virus (TRV). The virus is transmitted by the stubby root nematode (Paratrichodorus allius) in the Pacific Northwest potato producing regions. Alfalfa (Medicago sativa L.) and Scotch spearmint rarely serve as hosts for TRV. Therefore, P. allius reared on these plants for 1 to 3 months are cleansed of TRV in greenhouse trials. However, weeds in alfalfa and Scotch spearmint rotation crops may serve as hosts for the virus. In greenhouse trials, hairy nightshade (Solanum sarrachoides), prickly lettuce (Lactuca serriola), henbit (Lamium amplexicaule) and green foxtail (Setaria viridis) grown alone were found to be suitable hosts of P. allius, whereas Powell amaranth (Amaranthus powell) was not. Viruliferous P. allius added to hairy nightshade, prickly lettuce, henbit, green foxtail, or Powel amaranth in mixtures with alfalfa and/or Scotch spearmint occasionally remained viruliferous over a 3- to 4-month period, whereas P. allius maintained on weed-free alfalfa or Scotch spearmint became virus-free after 1 to 2 months. Potato grown in soil containing P. allius that were maintained on weed-alfalfa or weed-Scotch spearmint mixtures for 3- to 4-months exhibited slight to severe CRS symptoms on new tubers, whereas potato following weed-free Scotch spearmint or alfalfa were free from CRS symptoms. Severe CRS symptoms on potato tubers were only observed when potatoes were grown in soil containing P. allius that were maintained on hairy nightshade or hairy nightshade mixtures with alfalfa or Scotch spearmint. The presence of weeds that serve as hosts of both TRV and P. allius may nullify the positive effects of growing alfalfa or Scotch spearmint for CRS control. Targeted control efforts of known weed hosts may be required to successfully eliminate CRS from fields using alfalfa and Scotch spearmint rotational crops.