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Title: Use of Electrical Penetration Graph Technology to Examine Transmission of ‘Candidatus Liberibacter solanacearum’ to Potato by Three Haplotypes of Potato Psyllid (Bactericera cockerelli; Hemiptera: Triozidae)

item MUSTAFA, TARIQ - Washington State University
item Horton, David
item Cooper, William - Rodney
item Swisher Grimm, Kylie
item ZACK, RICH - Washington State University
item PAPPU, H.R. - Washington State University
item Munyaneza, Joseph - Joe

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2015
Publication Date: 9/25/2015
Citation: Mustafa, T., Horton, D.R., Cooper, W.R., Swisher, K.D., Zack, R.R., Pappu, H.R., Munyaneza, J.E. 2015. Use of Electrical Penetration Graph Technology to Examine Transmission of ‘Candidatus Liberibacter solanacearum’ to Potato by Three Haplotypes of Potato Psyllid (Bactericera cockerelli; Hemiptera: Triozidae). PLoS One. 10(9):e01 38946. doi:10.1371/journal.pone.0138946.

Interpretive Summary: Zebra chip, an economically important disease of potato in the United States is caused by the new bacterium Liberibacter, which is vectored by the potato psyllid. Researchers at USDA-ARS Wapato in Washington, in collaboration with scientists at Washington State University, assessed mechanisms by which this insect pest transmits the bacterium. It was determined that all known genetic variants or haplotypes of the potato psyllid were equally capable of transmitting the bacterium to potato, suggesting that all these psyllid variants need to be monitored and controlled. It was also determined that this pathogen was transmitted very rapidly by the potato psyllid, making it difficult to kill this insect vector fast enough before it can transmit the zebra chip pathogen. Information from this research underscores the urgent need to develop management tools that rely on repellency of the potato psyllid or prevention of its feeding on potato, rather than killing the psyllid sometime after it arrives on the crop, to prevent crop loss to the zebra chip disease.

Technical Abstract: The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is a vector of the phloem-limited bacterium ‘Candidatus Liberibacter solanacearum’ (Lso), the putative causal agent of zebra chip disease of potato. Little is known about how potato psyllid transmits Lso to potato. We used electrical penetration graph (EPG) technology to compare stylet probing activities and efficiency of Lso transmission of three haplotypes of potato psyllid (Central, Western, Northwestern). All haplotypes exhibited the full suite of stylet activities identified in previous studies with this psyllid, including intercellular penetration and secretion of the stylet pathway, xylem ingestion, and phloem activities, the latter comprising salivation and ingestion. The three haplotypes exhibited similar frequency and duration of probing activities, with the exception of salivation into phloem, which was of higher duration by psyllids of the Western haplotype. We manipulated how long psyllids were allowed access to potato (“inoculation access period”, or IAP) to examine the relationship between phloem activities and Lso transmission. Between 25 and 30% of psyllids reached and salivated into phloem at an IAP of 1 hr, increasing to almost 80% of psyllids as IAP was increased to 24 h. Probability of Lso-transmission was lower across all IAP levels than probability of phloem salivation, indicating that a percentage of infected psyllids which salivated into the phloem failed to transmit Lso. Logistic regression showed that probability of transmission increased as a function of time spent salivating into the phloem; transmission occurred as quickly as 5 min following onset of salivation. A small percentage of infected psyllids showed extremely long salivation events but nonetheless failed to transmit Lso, for unknown reasons. Information from these studies increases our understanding of Lso transmission by potato psyllid, and demonstrates the value of EPG technology in exploring questions of vector efficiency.