|RASHED, ARASH - University Of Idaho|
|WORKNEH, FEKEDE - Texas A&M University|
|PAETZOLD, LI - Texas A&M University|
|RUSH, CHARLES - Texas A&M University|
Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2017
Publication Date: 2/3/2017
Citation: Wallis, C.M., Rashed, A., Workneh, F., Paetzold, L., Rush, C. 2017. Effects of ‘Candidatus Liberibacter solanacearum’ infections on potato (Solanum tuberosum L.) tuber physiology when kept at different temperatures. American Journal of Potato Research. doi: 10.1007/s12230-017-9569-1.
Interpretive Summary: Current efforts to minimize processor losses due to zebra chip disease of potato (ZC), caused by infections of ‘Candidatus Liberibacter solanacearum’, involves visual inspection of symptoms in freshly-cut potatoes. Symptomatic lots are rejected prior to storage. However, late-season Lso-infections could result in the acceptance of Lso-positive but asymptomatic tubers that may develop ZC symptoms in storage. This study examined development of ZC symptoms, Lso titers, and associated shifts in tuber chemistry in late-season Lso-infected tubers held at 3°C, 6°C, or 9°C. Although changes in Lso titers were variable, symptoms were observed to be consistently greater in tubers kept at 3°C versus 6°C or 9°C. ZC-associated compounds were greater in Lso-infected tubers kept at 3°C compared to those stored at higher temperatures. These results confirmed ZC symptoms may develop in Lso-positive tubers that were asymptomatic at harvest. Based on these findings, PCR-detection of Lso presence should be made on potentially infected tubers prior to acceptance. Furthermore, any tubers suspected of being Lso-positive should be held at temperatures greater than 3°C to limit ZC symptom development.
Technical Abstract: The bacterium ‘Candidatus Liberibacter solanacearum’ (Lso) is the putative causal agent of zebra chip disease of potato (ZC), an emerging disease that causes substantial economic losses where endemic. Currently, potato processors examine a cross-section of tubers from afflicted areas and reject when tubers are observed bearing conspicuous browning symptoms. However, tubers infected by Lso a week or two prior to harvest may not yet be symptomatic upon harvest and may be deemed acceptable by processors. Yet, these late-infected tubers could develop ZC symptoms while in storage. The aim of this study was to observe ZC symptom development, Lso titer changes, and associated physiological shifts in tubers, asymptomatic at harvest, of two potato cultivars held at one of three different temperatures (3°C, 6°C, or 9°C). Fresh ZC symptoms were more severe in Red La Soda or Russet Norkotah tubers maintained at 3°C than at 6°C or 9°C. Likewise, tubers kept at 3°C had greater ZC symptoms after frying in oil than Red La Soda tubers kept at 6°C or Russet Norkotah tubers kept at 9°C. However, Lso titers were greatly variable in both cultivars and no firm conclusions could be made about storage temperature effects on disease. For many amino acids and phenolic compounds, levels in tubers kept at 3°C were greater than those kept at 6°C or 9°C. However, infection status effects on compound levels were variable. Based on these results, Lso-infection progression and associated ZC development were highly variable in stored tubers. Therefore, detection methods based upon visual assessment of symptoms in stored tubers could be problematic.