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Candidatus Liberibacter asiaticus’ cells remain viable in citrus seeds for several months

Marcus Vinicius Merfa: Department of Entomology and Plant Pathology, Auburn University

<div>Citrus huanglongbing (HLB) is currently the most devastating citrus disease worldwide, and in the US it is associated with the heretofore unculturable bacterium ‘<em>Candidatus</em> Liberibacter asiaticus’ (CLas). Although this pathogen is not seed-transmitted, several reports have shown that CLas can be found in citrus seeds, and our research group has been using seeds collected from symptomatic fruits as initial inoculum for research related to CLas. Thus, the goal of our study was to determine for how long CLas is viable in seeds of fruits stored in the laboratory at different temperatures. As a measurement of CLas viability, transcripts of the <em>rpo</em>B gene were quantified by RT-qPCR at different time points using fruits from trees showing HLB symptoms. The gene <em>cox1</em> from plant was used as internal control. We found that CLas remained viable in seeds for a period of three to six months after infected citrus fruits were sent to our laboratory in Alabama from Florida, Texas and Colombia. On the other hand, <em>rpoB </em>transcripts were not detected in control CLas-infected seeds when ampicillin was added. Factors influencing fruit decay reduced CLas viability. This is the first study using mRNA to assess viability of CLas in plant material, and results showed that this method could be applied to other viability studies of this microorganism.</div>