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Title: Insect-Phytoplasma/Bacteria Relationship: Case of Potato Purple Top and Zebra Chip Diseases

item Munyaneza, Joseph - Joe

Submitted to: Plant Pathogenic Bacteria International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/1/2008
Publication Date: 6/1/2009
Citation: Munyaneza, J.E. 2009. Insect-Phytoplasma/Bacteria Relationship: Case of Potato Purple Top and Zebra Chip Disease. pp 1-9. In: Proceedings of the 2008 International Symposium on Plant Pathogenic Bacteria, 17-18 September 2008, Guadalajara, Mexico. University of Guadalajara and Mexican Society of Phytopathology.

Interpretive Summary: Insect-transmitted diseases are a serious threat to potato production in North and Central America. Development of effective management strategies for these diseases requires thorough knowledge of the interaction between the plant pathogens and their insect vectors. USDA-ARS scientists at Wapato, WA, conducted extensive studies on purple top and zebra chip, two important and emerging insect-transmitted diseases of potato. It was found that potato purple top is caused by a phytoplasma transmitted by the beet leafhopper, whereas zebra chip is suspected to be caused by a bacterium and transmitted by the potato psyllid. Information from these studies will be presented at the 2008 International Symposium on Plant Pathogenic Bacteria at the University of Guadalajara in Mexico and will help affected potato growers in North and Central America minimize losses due to these damaging diseases by controlling their insect vectors.

Technical Abstract: Purple top and zebra chip are two important and emerging potato diseases in North and Central America. While purple top disease is well known to be caused by phytoplasmas and transmitted by leafhoppers, the exact causal agents and insect vectors of zebra chip are still unknown. The etiology of potato purple top in North America has generally been attributed to aster yellows phytoplasma. Recently, however, it has been shown that the potato purple top disease in the Pacific Northwest of the U.S. is caused by the beet leafhopper-transmitted virescence agent (BLTVA) phytoplasma. In North America, species of Macrosteles are considered the main vectors of the potato purple top phytoplasma. However, studies have shown that the potato purple top phytoplasma in the Columbia Basin of Washington and Oregon is vectored by the beet leafhopper (Circulifer tenellus) and not Macrosteles spp. as previously believed. Investigations to identify the exact zebra chip causal agents and vectors are currently underway. However, greenhouse and field studies conducted in Washington and the Lower Rio Grande Valley of Texas clearly showed that zebra chip was strongly associated with the potato psyllid (Bactericera cockerelli). Recent testing by PCR has also revealed the presence of a previously undescribed species of the bacterium ‘Candidatus Liberibacter’ in potato plants and tubers exhibiting typical symptoms of zebra chip. This bacterium has also been detected in potato psyllids. However, despite the association of this bacterium with zebra chip-infected material and potato psyllid, the role of this putative causal agent in zebra chip symptom expression and mechanisms by which it is transmitted by the potato psyllid to plants are not yet clear and need further investigation.