Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/18/2013
Publication Date: 6/7/2013
Citation: Wallis, C.M., Rashed, A., Wallingford, A.K., Rush, C.M. 2013. Different potato cultivars may vary in zebra chip symptoms and associated physiological changes when infected by 'Candidatus Liberibacter solanacearum'. Symposium Proceedings. p. 89-93. Interpretive Summary: Zebra chip disease (ZC), putatively caused by ‘Candidatus Liberibacter solanacearum’ (Lso), is of increasing concern for potato growers as it renders tubers unmarketable due to undesirable browning of fresh and fried potato products. Changes in tuber levels of amino acids, sugars, and phenolics have been observed to be associated with ZC symptom progression. However, these Lso-infection associated shifts in tuber physiology have only been observed in chipping potato cultivars. Anecdotal observations have concluded that red and russet tubers may exhibit reduced ZC symptoms compared to chipping varieties. Thus, this study examined changes in tuber physiology that occurred when red (Red La Soda), russet (Russet Norkota), or chipping (FL1867) potatoes were infected with Lso for one, two, three, or four weeks prior to harvest. At harvest, ZC symptoms, Lso titers, and tuber biochemical levels were assessed. Red potatoes exhibited more severe ZC symptoms than the russet or chipping cultivars when infected four weeks prior to harvest. At the same time, red potato tubers had significantly lowered levels of phenolics than russet or chipping potato tubers. ZC symptoms, Lso titers, and tuber biochemistry did not otherwise differ between cultivars. Regardless of cultivar, levels of most amino acids (excluding asparagine, aspartic acid, glutamine, glutamic acid, and methionine), fructose, glucose, and phenolics were greater in Lso-infected tubers than non-infected tubers, with levels increasing with Lso infection duration. These amino acids, reducing sugars, and phenolics were positively associated with ZC symptoms and Lso titers. In contrast, asparagine, aspartic acid, glutamine, glutamic acid, and methionine were greatest in tubers infected with Lso one week before harvest. These results demonstrated that physiological responses to Lso-infection were mostly consistent between potato cultivars, and increased levels of certain amino acids, fructose, glucose, and phenolics results in increased ZC symptom severity.
Technical Abstract: Zebra chip disease (ZC) is an increasingly important disease for potato production in the United States and elsewhere, as it causes undesirable browning symptoms in both fresh and fried potatoes. ZC is putatively caused by ‘Candidatus Liberibacter solanacearum’ (Lso), a bacterium which is spread by the potato psyllid. Previous studies have observed that ZC symptoms are due to changes in tuber physiology, especially increased phenolic, sugar, and amino acid content. However, ZC-associated shifts in tuber physiology only have been observed in chipping cultivars of potato. Anecdotal reports have observed that other cultivars of potato (such as red or russet potatoes) may exhibit fewer ZC symptoms when infected with Lso. Thus, this study examined the progression of ZC and associated changes in tuber biochemistry that occurred when three different potato cultivars (Red La Soda, Russet Norkota, and the chipping variety FL1867) were infected with Lso one, two, three, or four weeks prior to harvest. At harvest, tuber symptoms, Lso titers, and biochemistry were assessed. Contrary to anecdotal reports, red potato tubers were observed to have greater ZC severity than russet or chipping potato tubers. Red potatoes infected for four weeks had significantly lower levels of phenolics than russet or chipping potatoes. There were no significant differences in chemical levels between cultivars when the potatoes were infected for other durations. Regardless of cultivar, tubers infected for at least three weeks had greater levels of fructose, glucose, and overall phenolics than non-infected tubers. Levels of the amino acids asparagine, aspartic acid, glutamic acid, glutamine, and methionine were greatest in tubers infected for one or two weeks. However, levels of all other amino acids were greatest in tubers infected for four weeks. ZC symptoms and Lso titers were positively correlated with reducing sugar, phenolic, and amino acid levels, with the exception of asparagine, aspartic acid, glutamic acid, glutamine, and methionine. These results suggest that tuber physiological alterations generally are consistent among major varieties of commercially-grown potatoes.