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)

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 behaviors and efficiency of Lso transmission of three haplotypes of potato psyllid (Central, Western, Northwestern). All haplotypes exhibited the full suite of stylet behaviors 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 behaviors, 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.

Transmission of ‘Candidatus Liberibacter solanacearum’ by Bactericera trigonica Hodkinson to vegetable hosts

“…In our work, EPG waveforms were analogous to those described for other psyllids (Bonani et al, 2010;Civolani et al, 2011;Pearson et al, 2014;Mustafa et al, 2015) and those described for B. trigonica by Antolínez et al (2017c). Acquisition of the bacteria is associated with the phloem ingestion (E2 waveform), whereas inoculation is associated with salivation into the phloem sieve elements (E1 waveform) (Sandanayaka et al, 2014;Antolínez et al, 2017c).…”

“…These components provide information on stylet tip position in specific plant tissues, time spent at each location, and stylet activity (Tjallingii, 1985). The EPG waveforms of psyllids are reported for D. citri (Bonani et al, 2010;Cen et al, 2012b), B. cockerelli (Butler et al, 2012;Pearson et al, 2014;Sandanayaka et al, 2014;Mustafa et al, 2015), C. pyri L. (Civolani et al, 2011) and Psylla pyricola Förster (Ullman & McLean, 1988). Comparison by EPGs waveforms of the probing behaviours of males and females of B. trigonica in carrot has been recently reported (Antolínez et al, 2017a) and the characterization of the electrical penetration graphs (Antolínez et al, 2017b).…”

Vector mediated transmission of Candidatus Liberibacter solanacearum and epidemiological consequences

“…The Lso transmission is a complex process and it includes various steps. First, the psyllid vector acquires the bacterium from the phloem sieve elements of an infected plant during feeding (Mustafa et al, 2015;Sandanayaka et al, 2014). Once Lso reaches the psyllid digestive tract, the bacteria must pass through the midgut epithelium in order to reach the haemocoel and circulate in the haemolymph (Cicero et al, 2016;Fisher et al, 2014).…”

“…This process is directly linked to the inoculation and acquisition of 'Candidatus Liberibacter solanacearum' (Mustafa et al, 2015;Sandanayaka et al, 2014). This process cannot be seen directly but can be monitored very closely by using the Electrical Penetration Graph (EPG) technique (McLean and Kinsey, 1964;Tjallingii, 1978).…”

“…Thus it is possible to identify when the insect stylets puncture plant cell membranes (Tjallingii 1985). Because of this, EPG have been used to correlate insect-feeding activities with the transmission of intracellular plant pathogens such as Lso, viruses or phytoplasmas (Sandanayaka et al, 2014;;Mustafa et al, 2015;Munyaneza et al, 2016). Waveform D: Short waveform composed of two separate phases.…”