Latent Period and Transmission of “Candidatus Liberibacter solanacearum” by the Potato Psyllid Bactericera cockerelli (Hemiptera: Triozidae)

Abstract

“Candidatus Liberibacter solanacearum” (Lso) is an economically important pathogen of solanaceous crops and the putative causal agent of zebra chip disease of potato (Solanum tuberosum L.). This pathogen is transmitted to solanaceous species by the potato psyllid, Bactericera cockerelli (Šulc), but many aspects of the acquisition and transmission processes have yet to be elucidated. The present study was conducted to assess the interacting effects of acquisition access period, incubation period, and host plant on Lso titer in psyllids, the movement of Lso from the alimentary canal to the salivary glands of the insect, and the ability of psyllids to transmit Lso to non-infected host plants. Following initial pathogen acquisition, the probability of Lso presence in the alimentary canal remained constant from 0 to 3 weeks, but the probability of Lso being present in the salivary glands increased with increasing incubation period. Lso copy numbers in psyllids peaked two weeks after the initial pathogen acquisition and psyllids were capable of transmitting Lso to non-infected host plants only after a two-week incubation period. Psyllid infectivity was associated with colonization of insect salivary glands by Lso and with Lso copy numbers >10,000 per psyllid. Results of our study indicate that Lso requires a two-week latent period in potato psyllids and suggest that acquisition and transmission of Lso by psyllids follows a pattern consistent with a propagative, circulative, and persistent mode of transmission.

Risk assessment of ‘Candidatus Liberibacter solanacearum’ transmission by the psyllids Bactericera trigonica and B. tremblayi from Apiaceae crops to potato

“…Finally, in this Lso-psyllid interaction, it is possible that longer latency periods than normal are required for the replication of Lso in the psyllid body, which provides another explanation for the absence of transmission. However, we did not test for latency periods in B. tremblayi , and the only reported latency period for Lso is in B. cockerelli 29; therefore, additional research is recommended to fully understand the Lso infection process in this psyllid species.…”

“…Lack of transmission could be explained by different factors. For example, it has been reported that when Lso is acquired, the bacteria must pass through the insect midgut epithelium to infect the haemolymph and then enter the salivary glands1529. It is uncertain if Lso is able to complete circulation in the body of B. tremblayi since this process has not been studied in this psyllid species.…”

Vector mediated transmission of Candidatus Liberibacter solanacearum and epidemiological consequences

“…Current experimental evidence suggests that Lso is transmitted in a propagative-circulative manner, which means the bacteria replicate in their vectors and are inoculated in saliva secreted before phloem ingestion (Sandanayaka et al, 2014;Sengoda et al, 2014Cicero et al, 2016a;Mustafa et al, 2015). Previous reports have shown that Lso could be successfully inoculated in a single salivation event in a phloem sieve element by B. cockerelli (Mustafa et al 2015); Thus, it is likely that only small titres of bacteria inoculated are needed to achieve infection.…”

“…For example, it has been reported that when Lso is acquired, the bacteria must pass through the insect midgut epithelium to infect the haemolymph and then enter the salivary glands (Cicero et al, 2016ab;Sengoda et al, 2014). It is uncertain if Lso is able to complete circulation in the body of B. tremblayi since this process has not been studied in this psyllid species.…”

“…Second, the bacteria must replicate and circulate in the vector for a latency period. Finally, Lso must be inoculated during salivation before sap ingestion in the sieve elements of a non-infected plant Sengoda et al, 2014;Mustafa et al, 2015;). Therefore, detailed knowledge of vector stylet penetration activities is important for developing control strategies to prevent Lso transmission.…”