Submitted to: Potato Conference and Trade Fair Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 15, 2005
Publication Date: December 30, 2005
Citation: Munyaneza, J.E. 2005. Purple top disease and beet leafhopper transmitted virescence agent (BLTVA) phytoplasma in potatoes of the Pacific Northwest of the United States. pp. 211-220. In: A. J. Haverkort and P. C. Struik [eds.], "Potato in progress: science meets practice". Wageningen Academic Publishers. Interpretive Summary: In recent years, diseases caused by phytoplasmas have become increasingly important in vegetable crops of the Pacific Northwest. An epidemic of purple top disease of potato occurred in the Columbia Basin of Washington and Oregon in 2002 growing season and caused significant yield losses to potato fields as well as indications of reduced tuber quality resulting from diseased plants. The disease was also observed in 2003 and 2004 growing seasons, especially in potatoes that were not treated with insecticides, including organic potato fields. A multi-disciplinary team funded by Oregon and Washington State Potato Commissions and mainly made of entomologists and plant pathologists from USDA-ARS, universities, and potato industry in the area, was formed to investigate various aspects of the problem, including disease causal agent(s) identification, insect(s) vectoring the disease, disease epidemiology, and disease management. It was found that the potato purple top disease in the Columbia Basin is caused by the beet leafhopper transmitted virescence agent (BLTVA) phytoplasma. The beet leafhopper was found to be the principal carrier of BLTVA, and is the likely vector of the potato purple top phytoplasma in this region. Leafhoppers seem to invade the Columbia Basin potato fields around mid-May to mid-June from weeds in the vicinity of the fields. Information from the present study will help growers in the Columbia Basin make effective and environmentally sound management decisions to reduce losses to potatoes due to this purple top disease by monitoring and controlling beet leafhoppers.
Technical Abstract: Diseases caused by phytoplasmas are increasingly on the rise in potatoes of the Pacific Northwest of the United States. Recently, a serious epidemic of purple top disease of potato occurred in the Columbia Basin of Washington and Oregon and caused very significant losses to potato fields. There were also indications of reduced tuber quality resulting from infected plants. Potato fields with similar disease symptoms were also reported in some parts of Idaho. In addition, similar disease outbreaks have recently been observed in several vegetable crops grown in the Columbia Basin, including dry beans and radish grown for seed. Using polymerase chain reaction (PCR) technique, DNA analysis of samples of diseased plants collected from potato fields in various locations of the affected area revealed that the beet leafhopper transmitted virescence agent (BLTVA), a clover proliferation group phytoplasma, was the causal agent of the disease. Furthermore, investigation of the insects vectoring this potato purple top disease indicated that the causal phytoplasma was almost exclusively associated with the beet leafhopper, Circulifer tenellus Baker, suggesting that this insect is the major vector of the disease in this region. In 2003 and 2004, leafhopper sampling was conducted in the affected area to determine the seasonal occurrence and abundance of the beet leafhopper in this major potato growing region of the United States. The beet leafhopper was very abundant in weeds near potato fields from mid-April to mid-October. This leafhopper moved into potato fields sometime in mid-May and was present in potatoes throughout the remaining of the growing season. This insect was more abundant in potatoes in early summer than in late summer, suggesting that potatoes more likely are infected with the purple top disease during this time of the growing season; however, it is not clear how far into the growing season that potato infection occurs.