Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2010
Publication Date: 5/5/2010
Publication URL: http://hdl.handle.net/10113/44516
Citation: Miles, G.P., Samuel, M.A., Chen, J., Civerolo, E.L., Munyaneza, J.E. 2010. Evidence that Cell Death is Associated with Zebra Chip Disease in Potato Tubers. American Journal of Potato Research. 87:337-349. Interpretive Summary: Zebra chip (ZC) is a newly established and highly destructive disease of potato that occurs in several southwestern states of the United States, Mexico, Central America, and New Zealand. Tubers from ZC-affected potato plants exhibit dramatic browning of vascular tissue concomitant with necrotic flecking, both of which can affect the entire tuber. Upon frying, these tubers develop a characteristic striped pattern of discoloration rendering processed chips and fries unmarketable. Researchers at USDA-ARS Wapato and Parlier conducted studies to determine if cell death is associated with the ZC symptoms in tubers. Results revealed numerous, small, irregularly-shaped lesions throughout ZC-affected tubers, suggesting cell death is involved in the disease. The findings from this research will add to our basic understanding of the molecular and biochemical mechanisms underlying the disease process with the potential of developing effective strategies to reduce or eliminate ZC-induced tuber damage.
Technical Abstract: Zebra chip (ZC) is an established and highly destructive disease of potato (Solanum tuberosum L.) that occurs in several southwestern states of the United States, Mexico, Central America, and New Zealand. The causal agent for this disease has not been identified. However, the bacterium ‘Candidatus Liberibacter solanacearum’ and the potato psyllid, Bactericera cockerelli (Šulc), its insect vector, are associated with the disease. Tubers from ZC-affected potato plants exhibit dramatic browning of vascular tissue concomitant with “necrotic flecking” both of which can affect the entire tuber. Upon frying, these tubers develop a characteristic striped pattern of discoloration rendering them unmarketable. These characteristic ZC symptoms in the tubers have been suggested to be associated with general cell death, though no evidence to confirm this hypothesis has been shown. In order to determine if cell death is associated with ZC disease, a series of experiments were undertaken. Cell death was initially quantified by comparing cellular ion leakage from ZC-affected and ZC-free tubers. Levels of ion leakage were found to be significantly higher in ZC-affected tubers compared to ZC-free tubers. To examine further the association of cell death with ZC disease, ZC-affected and ZC-free tubers were compared using classical histochemical staining methods in conjunction with optical microscopy, which revealed layers of dead cells surrounding numerous, small, irregularly-shaped lesions throughout the parenchymatic medullary region, vascular ring and cortex of ZC-affected tubers. This cell death was confirmed using high-resolution, field-emission scanning electron microscopy (FE-SEM) of fresh-cut tuber tissue.