# Survey of ‘Candidatus Liberibacter solanacearum’ and Its Potential Psyllid Vectors in Northwestern Italy

## TL;DR

This study found the presence of a harmful bacterium and its insect carriers in crops in Italy, raising concerns about potential agricultural losses.

## Contribution

The study reports the first detection of CLso and its psyllid vectors in Northwestern Italy.

## Key findings

- CLso was detected in carrot plants and four psyllid species in the region.
- Bactericera nigricornis was the most common psyllid in potato fields.
- Haplotypes D and U of CLso were identified through sequencing.

## Abstract

Psyllids are a group of insects responsible for causing economic damage to crops both directly through their feeding behavior and indirectly, transmitting bacterial pathogens that circulate within plant sap from one plant to another. Among these pathogens, ‘Candidatus Liberibacter solanacearum’ (CLso) is associated with symptoms on plants of the Apiaceae and Solanaceae families. CLso was first reported in Europe in Finland followed by Norway and several other countries, with cases where it was linked to economic losses in carrot and celery crops. The presence of this bacterium in the region under study was unknown, prompting a survey to assess its presence and investigate potential psyllid vectors. The survey was conducted in Northwestern Italy, specifically in the Piedmont region. The bacterium was detected in carrot plant samples as well as in four psyllid species: Bactericera trigonica, Heterotrioza chenopodii, Bactericera nigricornis and Trioza urticae. This report highlights the need for further investigation into the spread dynamics of the bacterium in other areas, to mitigate potential risks to agriculture.

Psyllids (Hemiptera: Psylloidea) are the main vectors of various phloem-limited plant pathogens, including ‘Candidatus Liberibacter’ species. ‘Candidatus Liberibacter solanacearum’ (CLso) has been associated with various plant disorders and economic losses in plants from the Solanaceae and Apiaceae families. Recently, it has been reported in Europe, primarily linked to carrots and celery. This situation presents a significant threat, prompting the need for a survey to assess the presence of the bacterium and its potential vectors. Plant and psyllid samples were collected from potato (Solanum tuberosum), carrot (Daucus carota) and other wild weed species in commercial fields and urban areas over two consecutive years (2022 and 2023). DNA was extracted from the samples, followed by conventional PCR and the sequencing of positive samples. The psyllid species Bactericera nigricornis was the dominant species in potato fields, while Bactericera trigonica was the most abundant in carrot fields, followed by Heterotrioza chenopodii, ranking as the second most abundant species in both cases. CLso-positive samples were found in D. carota, B. trigonica, H. chenopodii, B. nigricornis, and Trioza urticae. The sequencing results suggest the detected haplotypes are D and U. These findings raise concerns about the potential spread of CLso and the associated risk of significant economic losses.