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78 POTATO GROWER | JANUARY 2018 Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In FOOD SCIENCE | By Christopher M. Wallis & John T. Trumble Developing zebra chip tolerance from a food science perspective Infected but Unaffected Zebra chip disease is a major problem for potato growers worldwide due to its ability to greatly diminish yield and tuber quality in afflicted plants. Zebra chip is caused by a bacterium named Candidatus Liberibacter solanacearum (Lso), which is spread between plants by the potato psyllid insect. Current best management practice is to prevent the spread of zebra chip by controlling the vector through the use of insecticides. However, potato psyllids are developing insecticide resistance, so control is becoming more challenging. Novel management options such as the development of resistant cultivars are therefore necessary to ensure long-term mitigation of zebra chip disease. Major screening efforts have been conducted to find zebra chip resistance in existing potato breeding lines, which often contain wild potato relatives in their backgrounds. Out of hundreds of potato breeding lines, a handful were discovered that did not have observable zebra chip symptoms when infected despite becoming positively infected by Lso. The major symptom of zebra chip disease is brown discoloration that occurs when potato tubers are freshly sliced or when fried. Food science has determined the reasons behind this symptom. The increased browning of freshly sliced tubers is due to the increase of plant-produced compounds called chlorogenic acids, the same compounds found in apples that result in brown discoloration after a bite is taken. This is called enzymatic browning because a plant enzyme protein converts the chlorogenic acid to a brown pigment when exposed to oxygen in the air.