‘Candidatus Liberibacter europaeus’ sp. nov. that is associated with and transmitted by the psyllid Cacopsylla pyri apparently behaves as an endophyte rather than a pathogen

Abstract

Summary ‘Candidatus Liberibacter spp.’ cause serious plant diseases. ‘Candidatus Liberibacter asiaticus’, ‘Ca. L. americanus’ and ‘Ca. L. africanus’ are the aetiological agents of citrus greening (Huanglongbing) in Asia, America and Africa. ‘Candidatus Liberibacter solanacearum’ causes diseases in Solanaceae in America and New Zealand. All four species are vectored by psyllid insects of different genera. Here, we show that the pear psyllid pest Cacopsylla pyri (L.) hosts a novel liberibacter species that we named ‘Ca. Liberibacter europaeus’. It can bloom to high titres in the psyllid host, with more than 109 16S rRNA gene copies per individual. Fluorescent in situ hybridization experiments showed that ‘Ca. L. europaeus’ is present in the host midgut lumen, salivary glands and Malpighian tubules. ‘Candidatus L. europaeus’ has a relatively high prevalence (> 51%) in C. pyri from different areas in the Piedmont and Valle d'Aosta regions in Italy and can be transmitted to pear plants in experimental transmission trials. However, even though high titres of the bacterium (more than 108 16S rRNA gene copies g−1 of pear plant tissue) could be detected, in the pear tissues no specific disease symptoms could be observed in the infected plants over a 6‐month period. Despite liberibacters representing potential quarantine organisms, ‘Ca. L. europaeus’, first described in Italy and Europe, apparently behaves as an endophyte rather than a pathogen.

Genetic diversity of ‘Cadidatus Liberibacter solanacearum’ strains in the United States and Mexico revealed by simple sequence repeat markers

“…This was followed by another report of non-pathogenic Liberibacter species named as 'Ca. L. europaeus' naturally vectored by the pear psyllid pest Cacopsylla pyri (L.) in Italy (Raddadi et al 2011). Based on these research findings, it is reasonable to assume that 'Ca.…”

“…L. americanus' (Lam), are associated with citrus huanglongbing (HLB) (Bové 2006), and another one, 'Ca. L. europaeus' is found as non-pathogenic in pear plants (Raddadi et al 2011).…”

SEC-Translocon Dependent Extracytoplasmic Proteins of Candidatus Liberibacter asiaticus

“…Besides HLB, Liberibacters are also known to cause many other plant diseases (Jagoueix et al, 1994; Teixeira et al, 2005; Hansen et al, 2008; Liefting et al, 2008; Raddadi et al, 2011) For example, Ca. L. solanacearum (Lso; Liefting et al, 2009) has been known to cause Zebra chip of potato and to infect peppers and tomatoes.…”

Liberibacter crescens gen. nov., sp. nov., the first cultured member of the genus Liberibacter

“…All previously described species of the genus 'Ca. Liberibacter' are transmitted through an insect vector of the family Psyllidae (Capoor et al, 1967;Hansen et al, 2008;Raddadi et al, 2011). Whether BT-1 T inhabits an insect host is unknown; however, the leafhopper Empoasca papayae is recommended for further study due to previous documentation of its association with phloem-limited bacteria in papaya (Pérez et al, 2010).…”