‘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

‘Candidatus Liberibacter sp.’ causes serious plant diseases. ‘Ca. L. asiaticus’, ‘Ca. L. americanus’ and ‘Ca. L. africanus’ cause citrus greening (Huanglongbing) in Asia, Americas and Africa. ‘Ca. L. solanacearum’ causes diseases in solanaceae in America and New Zealand. All of the 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 titers in the psyllid host, with more than 109 16S rRNA gene copies per individual. Fluorescent in situ hybridization experiments showed that ‘Ca. L. europaeus’ proliferates in the host gut, salivary glands and Malpighian tubules. ‘Ca. L. europaeus’ has a relatively high prevalence (> 51%) in C. pyri from different areas in Piedmont and Val d’Aosta regions in Italy and it can be transmitted to pear plants in experimental transmission experiments. However, even though high titers 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 symptomps could be observed in the infected plants over a one year period. ‘Ca. L. europaeus’ represents the first liberibacter with quarantine potential described in Italy and Europe