Assessing the likelihood of transmission of ‘Candidatus Liberibacter solanacearum’ to carrot by potato psyllid, Bactericera cockerelli (Hemiptera: Triozidae)

Authors: Munyaneza, Joseph - Joe; MUSTAFA, TARIQ - Washington State University; FISHER, TONJA - University Of Arizona; SENGODA, VENKATESAN - California Seed And Plant Labs; Horton, David

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2016
Publication Date: 8/15/2016
Citation: Munyaneza, J.E., Mustafa, T., Fisher, T., Sengoda, V., Horton, D.R. 2016. Assessing the likelihood of transmission of ‘Candidatus Liberibacter solanacearum’ to carrot by potato psyllid, Bactericera cockerelli (Hemiptera: Triozidae). PLoS One. 11(8):e0161016. doi:10.1371/journal.pone.0161016.

Interpretive Summary: Liberibacter is a phloem-limited bacterium that severely affects important crops, including potato and carrot. This bacterium is transmitted to potato by potato psyllids and to carrot by carrot psyllids. Researchers at USDA-ARS Wapato in Washington assessed whether potato psyllids can transmit this plant pathogen to carrot, leading to disease symptom development. It was discovered that, while potato psyllids survived on carrot for several weeks when confined on the plants under controlled laboratory and field conditions, the insects generally avoided feeding on the carrot phloem tissue, thereby failing to infect carrot plants with Liberibacter. Information from this study suggests that the risk of Liberibacter infection and spread between potato and carrot crops is negligible.

Technical Abstract: ‘Candidatus Liberibacter solanacearum’ (Lso) is a phloem-limited bacterium that severely affects important Solanaceae and Apiaceae crops, including potato, tomato, pepper, tobacco, carrot and celery. This bacterium is transmitted to solanaceous species by potato psyllid, Bactericera cockerelli, and to Apiaceae by carrot psyllids, including Trioza apicalis and Bactericera trigonica. Five haplotypes of Lso have so far been described, two are associated with solanaceous species and potato psyllids, whereas the other three are associated with carrot and celery crops and carrot psyllids. Little is known about cross-transmission of Lso to carrot by potato psyllids or to potato by carrot psyllids. Thus, the present study assessed whether potato psyllid can transmit Lso to carrot and whether Lso haplotypes infecting solanaceous species can also infect carrot and lead to disease symptom development. In addition, the stylet probing behavior of potato psyllid on carrot was assessed using electropenetrography (EPG) technology to further elucidate potential Lso transmission to Apiaceae by this potato insect pest. Results showed that, while potato psyllids survived on carrot for several weeks when confined on the plants under controlled laboratory and field conditions, the insects generally failed to infect carrot plants with Lso. Only three of the 200 carrot plants assayed became infected with Lso and developed characteristic disease symptoms. Lso infection in the symptomatic carrot plants was confirmed by polymerase chain reaction assay and Lso in the carrots was determined to be of the haplotype B, which is associated with solanaceous species. EPG results further revealed that potato psyllids readily feed on carrot xylem but rarely probe into the phloem tissue, explaining why little to no Lso infection occurred during the controlled laboratory and field cage transmission trials. Results of our laboratory and field transmission studies, combined with our EPG results, suggest that the risk of Lso infection and spread between psyllid-infested solanaceous and Apiaceae crops is likely to be uncommon under normal field conditions.