Abstract
‘Candidatus Liberibacter solanacearum’ is an important pathogen of Solanaceous crops that causes zebra chip disease of potato. This pathogen is transmitted among plants by the potato psyllid Bactericera cockerelli. Within-plant spatial variability in Liberibacter infection impedes the ability to detect the bacterium before the onset of visible symptoms. The goal of our study was to test whether vascular architecture of potato explains the uneven distribution of Liberibacter after inoculation of leaves. The movement of rhodamine B among leaves was used to identify vascular connectivity among leaves. Three weeks after inoculating a single leaf with Liberibacter, the pathogen infected significantly more leaflets that had direct vascular connectivity with the inoculated leaf than leaflets with minimal connectivity. In a separate study, significantly more psyllids confined to whole leaves with direct vascular connectivity to a Liberibacter-infected leaf acquired the pathogen than did psyllids confined to leaves with indirect or partial connectivity to the infected leaf. Using fluorescence in situ hybridization, the pathogen was observed in the inner and outer phloem above and below the export leaf, respectively, corresponding with passive movement of Liberibacter in the phloem. Results of this study indicate that the distribution of Liberibacter in potato is at least partly limited by vascular architecture. This knowledge should improve the design of sampling methods to detect Liberibacter in asymptomatic plants.
Highlights
Abstract ‘Candidatus Liberibacter solanacearum’ is an important pathogen of Solanaceous crops that causes zebra chip disease of potato
Results of this study suggest that the transport of ‘Ca. Liberibacter solanacearum’ from the inoculation leaf to other leaves is at least partially limited by vascular connectivity
The role of vascular architecture in contributing to withinplant variability of Liberibacter infection is supported by 1) significantly more leaflets with direct vascular connectivity with the inoculation leaf compared with those with minimal connectivity becoming infected with Liberibacter 3 weeks after the initial inoculation, 2) significantly greater acquisition of Liberibacter by psyllids confined to leaves with direct vascular connectivity with the inoculation leaf compared with psyllids confined to leaves with minimal or partial connectivity, and 3) the presence of Liberibacter in the inner phloem above the inoculation leaf and in the outer phloem below the inoculation leaf
Summary
Abstract ‘Candidatus Liberibacter solanacearum’ is an important pathogen of Solanaceous crops that causes zebra chip disease of potato. This pathogen is transmitted among plants by the potato psyllid Bactericera cockerelli. Results of this study indicate that the distribution of Liberibacter in potato is at least partly limited by vascular architecture. ‘Candidatus Liberibacter solanacearum’ is a pathogen of Solanaceous crops that causes zebra chip disease of potato (Solanum tuberosum L.) (Munyaneza 2012). Liberibacter is transmitted among plants by the potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), which acquires the pathogen by feeding on infected phloem. One possible explanation for within-plant variability in Liberibacter distribution is limitations imposed by vascular architecture or connectivity among leaves. Genes involved in cell-adhesion and self-mobility have been identified from ‘Ca. Liberibacter solanacearum,’ so within-plant distribution of this pathogen in potato may follow similar patterns observed for phytoplasmas (Lin et al 2011)
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