Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/25/2012
Publication Date: 5/25/2012
Citation: Rashed, A., Wallis, C.M., Simmons, A., Paetzold, L., Workneh, F., Rush, C.M. 2012. The effects of Zebra Chip disease development and bacterial titer on biochemical properties in relation to the time of infection. In: Workneh F. Rashed A. Rush CM (eds). Proceedings of the 11th annual SCRI zebra chip reporting session. Fredric Printing, Aurora, NY. p.65-69. Interpretive Summary: Zebra chip disease (ZC) is causing increasing problems for potato growers in the United States and elsewhere. ZC symptoms include increased browning of sliced and fried tubers which are unmarketable. However, knowledge about the biochemical makeup of ZC diseased tubers is only emerging. This research examines the development of symptoms and biochemical changes in ZC-infected tubers over time by inoculating potatoes at different intervals to harvest and assessment. This study also examined whether biochemical changes and symptom development varies within the same infected tuber; that is, whether differences exist between the top (stolon) end and bottom (apical) end of the tuber. Phenolic compounds, amino acids, and host defense-associated enzymes (such as polyphenol oxidases) were found present in greater amounts in tubers which had a longer disease incubation period before harvest, i.e. those infected first. Longer disease incubation periods also possessed greater ZC-symptoms. Symptoms as well as levels of phenolics were greater on the stolon ends of tubers than apical ends. The population levels of the putative causal agent of ZC, 'Candidatus' Liberibacter solanacearum, were observed to be non-correlated with ZC symptoms or changes in host chemistry.
Technical Abstract: Potato tuber biochemical responses to ‘Candidatus’ Liberibacter solanacearum (Lso), the causal agent of Zebra chip disease, were evaluated both within infected tubers and across different infection dates. Tuber biochemistry also was related to symptom severity and bacterial titer. Symptom severity was significantly greater at the terminal end (stolon attachment) compared to the apical end of infected tubers. However, bacterial populations did not differ between the two positions. Greater symptom severity at the terminal end was associated with increased levels of amino acids and total phenolics. Regarding different infection dates, amino acid concentrations did not differ although greater phenolic, peroxidase, and chitinase levels were observed with early inoculation dates. A negative correlation was observed between tuber symptom severity and peroxidase, chitinase, and phenolic compounds. The results confirmed that tuber physiological changes in response to Lso infection were directly affected by the time of inoculation and were associated with Zebra chip symptom severity. Plant responses appeared to be independent from Lso titers. Pathogen induced changes in tuber biochemistry may explain reduced germination rates of Zebra chip infected potato seed tubers.