1a. Objectives (from AD-416):
1. Observe development of zebra chip in potato tubers from plants infected late season (< 2 wks. before harvest). 2. Determine how titers of CLso in infected tubers change over time in storage. 3. Relate changes in phenolic, amino acid, and carbohydrate compound levels to zebra chip symptoms and CLso titers.
1b. Approach (from AD-416):
Collaborators from Texas AgriLife Research (Texas A&M University) will inoculate two different cultivars of potato and place into storage. After 0.5, 1, 2, and 3 months of storage, they will evaluate symptom development and harvest tubers to be used for chemical analyses. High performance liquid chromatography will be used on collected potato tuber samples to assess phenolic and carbohydrate levels, and gas chromatography will be used to assess amino acid levels. Quantitative PCR will be used to assess CLso titers. Univariate ANOVAs will determine which compounds are significantly increased in infected tubers compared to equivalent non-infected controls. Pearson’s or Spearman’s correlations, as appropriate, will find associations between chemistry, symptoms, CLso titers, and time in storage.
3. Progress Report:
This research is in support of Objective 2 (the goal of which is to elucidate molecular interactions of plant hosts and bacterial pathogens) of the in-house project. Little is known about the development of zebra chip disease (ZC), caused by ‘Candidatus Liberibacter solanacearum’ (Lso), after potato tubers are harvested. Lso-infected tubers were harvested and placed into cold storage for four months, with samples analyzed once a month for ZC severity and Lso titer by qPCR. Tubers then were left at room temperature for one, two, or three weeks post-storage to observe changes in ZC severity, Lso titer, or ZC-associated biochemistry when removed from storage. Results indicate that Lso-infected tubers had greater levels of the amino acid glycine than non-infected tubers. However, levels of the amino acid phenylalanine and four phenolics (chlorogenic acid, two flavonoid glycosides, and gallic acid) were greater in healthy tubers than infected tubers. Levels of the amino acids lysine and histidine changed over the sampling period. These initial results affirm the role of physiological changes in progression of zebra chip disease of potato. Knowledge gained about how ZC progressed in stored tubers should aid in optimizing storage and processing conditions to manage ZC.