Abstract: '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 10(9) 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 10(8) 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.
Abstract: Diversity of bacterial endophytes associated with grapevine leaf tissues was analyzed by cultivation and cultivation-independent methods. In order to identify bacterial endophytes directly from metagenome, a protocol for bacteria enrichment and DNA extraction was optimized. Sequence analysis of 16S rRNA gene libraries underscored five diverse Operational Taxonomic Units (OTUs), showing best sequence matches with gamma-Proteobacteria, family Enterobacteriaceae, with a dominance of the genus Pantoea. Bacteria isolation through cultivation revealed the presence of six OTUs, showing best sequence matches with Actinobacteria, genus Curtobacterium, and with Firmicutes genera Bacillus and Enterococcus. Length Heterogeneity-PCR (LH-PCR) electrophoretic peaks from single bacterial clones were used to setup a database representing the bacterial endophytes identified in association with grapevine tissues. Analysis of healthy and phytoplasma-infected grapevine plants showed that LH-PCR could be a useful complementary tool for examining the diversity of bacterial endophytes especially for diversity survey on a large number of samples.
Abstract: Plum pox virus (family Potyviridae, genus Potyvirus, PPV) is one of the most important viral pathogens of plants in the genus Prunus, particularly Prunus persica L. The role of the Myzus persicae (Sulzer) (Hemiptera: Aphididae) as a vector of PPV-M, and its role in spreading PPV-M, was investigated. PPV-M-infected peach trees were used as inoculum sources, and transmission to 15 herbaceous species commonly present in and around peach orchards was evaluated. The presence of PPV-M in secondary hosts after aphid transmission was verified by reverse transcription-polymerase chain reaction tests. The results indicate that Saponaria ocymoides L., Pisum sativum L., Trifolium repens L., Trifolium pratense L., Lepidium sativum L., Matricaria chamomilla L., Centaurea cyanus L., Bellis perennis L., Papaver rhoeas L., and Zinnia elegans L. became infected. Although Lupinus polyphyllus Lindley, Taraxacum officinale L., Achillea millefolium L., Amaranthus retroflexus L., and Linum rubrum L. did not become infected, they are hosts of M. persicae. Among the 10 positive species that were infected, the species most common in peach orchards, T. pratense, T. repens, B. perennis, and M. chamomilla, were used as source plants for the transmission studies to the peach tree. Our study reveals the ability of M. persicae to transmit PPV-M from herbaceous hosts to peach trees, describes PPV-M symptoms in herbaceous species, and discusses the role of M. persicae and its hosts as a source of PPV-M in peach orchards.