Characterizing zebra chip symptom severity and identifying spectral signatures associated with Candidatus Liberibacter solanacearum infected potato tubers

Authors: ZHAO, ZHIGUO - Shanxi University; PRAGER, SEAN - University Of Saskatchewan; CRUZADO, REGINA - University Of Idaho; LIANG, XI - University Of Idaho; Cooper, William - Rodney; Hu, Gongshe; RASHED, ARASH - University Of Idaho

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2018
Publication Date: 9/18/2018
Publication URL: http://handle.nal.usda.gov/10113/6108145
Citation: Zhao, Z., Prager, S., Cruzado, R., Liang, X., Cooper, W.R., Hu, G., Rashed, A. 2018. Characterizing zebra chip symptom severity and identifying spectral signatures associated with Candidatus Liberibacter solanacearum infected potato tubers. American Journal of Potato Research. 95(5):584-596. https://doi.org/10.1007/s12230-018-9666-9.
DOI: https://doi.org/10.1007/s12230-018-9666-9

Interpretive Summary: Zebra chip is an economically important disease of potato that causes discoloration in tubers. In collaboration with researchers at the University of Idaho and University of Saskatchewan, ARS scientists in Wapato, WA and Aberdeen, ID developed methods using visible and infrared spectrometry and infrared thermal imaging to identify infection in tubers and to predict severity of zebra chip symptoms. These methods will improve research to identify potato cultivars that are resistance to zebra chip disease, and could be developed into technology for growers and processors to screen harvested tubers for infection.

Technical Abstract: Zebra chip (ZC) is a disease of potatoes, which is associated with the bacteria ‘Candidatus Liberibacter solanacearum’ (Lso). Lso is transmitted by the potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae). ZC reduces yield and quality, as it results in discoloration of the vascular tissue within tubers. The severity of symptoms is affected by the time of infection, with early-season infections being associated with high symptom expression. Although tubers infected late in the growing season, i.e. within two weeks of harvest, express minimal to no symptoms, they may proceed to express ZC symptoms during storage. Currently, visualization of ZC symptoms in tubers is used by processors to estimate the percentage of ZC-affected tubers in truckloads of potatoes. This approach, however, is time consuming and relies on evaluations of a small sample size. Thus, it is likely to fail in detecting the asymptomatic late infections. Using several potato genotypes infected at different times during the growing season, this study was set to determine if visible and near infrared spectrometry, and infrared thermal imaging, can be used to distinguish ZC-affected tubers, and to predict the severity of ZC symptoms. The subjective symptom score categorization, commonly used in ZC studies, corresponded with the percentage of the symptomatic area in the tubers sliced at the solon attachment end. The percentage of symptomatic area was also correlated with Lso titer. The reflectance at 582-nm bandwidth effectively distinguished healthy/asymptomatic tubers with high accuracy. Moreover, infrared thermal imaging was promising in distinguishing tubers based on Lso infection status. The objective measure of ZC severity, and the effectiveness of visual wavelengths and infrared thermal photography in distinguishing asymptomatic tubers are not only expected to facilitate selection assays for ZC resistance, but also have the potential for further development into a technology, facilitating screening of the ZC-affected tubers by the potato industry.