By P. B. Hamm and C. M. Ocamb
Cause A phloem-limited bacterium, 'Candidatus Liberibacter solanacearum,' which is transmitted by the potato psyllid (Bactericera cockerelli), and probably present in seed tubers. Originally a problem in Mexico by 1994, this disease was eventually reported in Texas and has since been reported around the United States, including in the PNW during 2011. Optimum temperature for disease development is 80°F to 90°F but transmission can occur at temperatures as cool as 54°F. In addition to potato, other cultivated (tomato and pepper) and wild solanaceous species are host to this pathogen. Zebra chip symptoms closely resemble potato purple-top, a phytoplasma caused disease, and psyllid yellows, a symptom resulting from feeding by the potato psyllid. While the vector of this disease is commonly found arriving in the PNW by mid to late season, apparently these insects do not always carry the bacterium. It is unknown at this time if this disease will be found yearly in the region in the future. The importance of seed as a source of this bacterium is not fully known at this time.
Symptoms Affected plants exhibit stunting, chlorosis or purplish coloration of leaves, leaf curling or scorching, aerial tuber formation, swollen internodes, and "bushy" plants due to axial bud elongation. Plants often die prematurely following infection. This disease can be confused with purple top or psyllid yellows.
In tubers dark stripes of necrotic tissue form, beginning on the stem end, especially in and around vascular tissue, and are very prominent when affected tubers are used for making chips or fries. A dark and sunken stolon attachment may be evident on some tubers. Steam-peeled tubers of 'Russet Burbank', 'Ranger Russet', and 'Umatilla Russet' appear darker compared to healthy tubers.
Cultural control
- Plant certified seed.
- Kill volunteer solanaceous around potato fields.
Chemical control Zebra chip cannot be controlled directly in potato but growers can indirectly control this disease by controlling the vector, the potato psyllid. For materials, rates, and procedures, consult the PNW Insect Management Handbook.
References Crosslin, J.M., Olsen, N., and Nolte, P. 2011. First report of zebra chip and Candidatus Liberibacter solanacearum on potatoes in Idaho. Plant Disease 96:453
Munyaneza, J.E., Sengoda, V.G., Buchman, J.L., and Fisher, T.W. Effects of temperature on "Candidatus Liberibacter solanacearum" and zebra chip potato disease symptom development. Plant Disease 96:18-23
Wen, A., et al. 2009. Detection, distribution, and genetic variability of 'Candidatus Liberibacter' species associated with zebra complex disease of potato in North America. Plant Disease 93:1102-1115.