Limited movement of Candidatus Liberibacter asiaticus in split-root citrus provides a model system for local and systemic effects of Huanglongbing
Jeane Dayse Veloso Dos Santos: UNESP Jaboticabal
<div>The phloem-limited bacterium <em>Candidatus</em> Liberibacter asiaticus (Las) causes Huanglongbing (HLB), the most devastating citrus disease worldwide. Transmitted by the Asian citrus psyllid, Las quickly moves into the root system and causes root dieback while simultaneously stimulating root growth. In the canopy, Las causes phloem-plugging, blotchy mottle, branch dieback, leaf drop, small and misshapen fruit, and premature fruit drop. To develop treatments for HLB, it is important to understand the movement of Las between leaf and root tissues and local and systemic effects of Las on the tree. In previous split-root experiments, lateral movement of Las occurred rapidly when inoculated above the split. Developing a split-root system with Las only present in one half of the root system would assist movement and pathogenesis studies. By using split-root rhizotrons and graft inoculating below the trunk split as the fall root flush begins, the Las infection remained isolated in the inoculated half of the root system for at least 2 months. Additionally, throughout the fall root flush and into dormancy, Las was undetectable in the canopy. This provides a model system for comparison of root growth, dieback, and transcriptional responses to local infection and systemic effects caused by distant infection with healthy controls. This differential infection of split roots also enable study of conditions that allow upward movement of Las by canopy manipulation.</div>
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