Identification of Plant DNA in Adults of the Phytoplasma Vector Cacopsylla picta Helps Understanding Its Feeding Behavior.

Dana Barthel,Hannes Schuler,Katrin Heer,Daniel Burckhardt,Katrin Janik,Luigimaria Borruso,Jacob Geier,Jonas Galli

doi:10.3390/insects11120835

Abstract

Simple SummaryCacopsylla picta is an insect vector of apple proliferation phytoplasma, the causative bacterial agent of apple proliferation disease. In this study, we provide an answer to the open question of whether adult Cacopsylla picta feed from other plants than their known host, the apple plant. We collected Cacopsylla picta specimens from apple trees and analyzed the composition of plant DNA ingested by these insects. By applying a state-of-the art sequencing approach, we show, for the first time, that Cacopsylla picta feeds from a wide range of woody and herbaceous plant species. Our results are important for a better understanding of the biology and feeding behavior of Cacopsylla picta. Since this insect is an efficient vector of apple proliferation phytoplasma, our results are also important to define potential reservoir plants that might be involved in the transmissive cycle of this pathogen. This study thus provides important data of practical relevance.Apple proliferation is an economically important disease and a threat for commercial apple cultivation. The causative pathogen, the bacterium ‘Candidatus Phytoplasma mali’, is mainly transmitted by Cacopsylla picta, a phloem-feeding insect that develops on the apple tree (Malus spp.). To investigate the feeding behavior of adults of the phytoplasma vector Cacopsylla picta in more detail, we used deep sequencing technology to identify plant-specific DNA ingested by the insect. Adult psyllids were collected in different apple orchards in the Trentino-South Tyrol region of northern Italy. DNA from the whole body of the insect was extracted and analyzed for the presence of plant DNA by performing PCR with two plant-specific primers that target the chloroplast regions trnH-psbA and rbcLa. DNA from 23 plant genera (trnH) and four plant families (rbcLa) of woody and herbaceous plant taxa was detected. Up to six and three plant genera and families, respectively, could be determined in single specimens. The results of this study contribute to a better understanding of the feeding behavior of adult Cacopsylla picta.

Highlights

Apple proliferation (AP) is an economically important disease in commercial apple cultivation and is caused by the cell wall-less bacterium ‘Candidatus Phytoplasma mali’ [1]
As deep sequencing approaches are sensitive to contamination, we investigated the effect of airborne pollen contamination in five C. picta specimens, which were caught with a beating tray in the sampling location Tenna/Bosentino in May 2015
Sequencing of the rbcLa amplicon revealed five operational taxonomic unit (OTU) that could not be unambiguously assigned to a particular genus but only to a plant family

Summary

Introduction

Apple proliferation (AP) is an economically important disease in commercial apple cultivation and is caused by the cell wall-less bacterium ‘Candidatus Phytoplasma mali’ [1]. Tasteless and colorless fruits that are not marketable [3]. ‘Ca. P. mali’ infects Malus spp., but the pathogen could be detected in wild and ornamental plants (reviewed in Janik et al.; [5]). The bacterium colonizes the phloem, and C. picta can, acquire the pathogen during feeding on an infected plant. Due to saliva release during psyllid feeding activity, the pathogen can be further transmitted to new plants [12]. As C. picta can transmit ‘Ca. P. mali’ transovarially to its progeny, a single mother individual can produce hundreds of infected descendants and even a small

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