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Population genomic analysis of factors influencing Phytoplasma transmission

Project Leader
Stauffer Christian, BOKU Project Leader
Duration:
01.02.2020-31.01.2023
Programme:
Joint Projects
EU-Project Instruments
Collaborative Project
Type of Research
Basic Research
Project partners
Fondazione Edmund Mach, Italy.
Contact person: Dr. Omar Rota-Stabelli;
Function of the Project Partner: Partner
Freie Universität Bozen, Italy.
Contact person: Dr. Hannes Schuler;
Function of the Project Partner: Partner
Research Centre Laimburg, Laimburg 6 , 39040 Auer (BZ), Italy.
Contact person: Dr. Katrin Janik;
Function of the Project Partner: Partner
University of Turin, Via Verdi, 8, 10124 Turin, Italy.
Contact person: Dr. Rosemarie Tedeschi ;
Function of the Project Partner: Partner
Staff
BOKU Research Units
Institute of Forest Entomology, Forest Pathology and Forest Protection
Funded by
Fonds zur Förderung der wissenschaftlichen Forschung (FWF) , Sensengasse 1, 1090 Wien, Austria
Abstract
Phytoplasmas are obligatory endosymbiontic bacteria that colonize the phloem of many plant species and cause hundreds of plant diseases worldwide. In nature, phytoplasmas are primarily transmitted by hemipteran vectors of the families Cicadellidae, Cixiidae, and Psyllidae. While, in principle, all phloem sucking insects could transmit phytoplasmas, only a limited number of species have been confirmed as vectors. This is because the transmission efficiency of phytoplasmas is a function of the complex tripartite association between the insect vector, the host plant, and the phytoplasma itself. Recent findings revealed that the microbial communities of both the insect vector and the host plant may interfere with phytoplasma transmission, making this system an even more complex multipartite one.
Apple proliferation (AP) is a disease caused by the phytoplasma ‘Candidatus Phytoplasma mali’, causing proliferation of auxiliary shoots and a decrease in fruit size and quality. It is not possible to cure infected apple trees, and the only way to limit the spread of the disease is to completely remove infected trees from the orchards. ‘Candidatus P. mali’ is mainly vectored between apple trees by two psyllids, Cacopsylla picta and Cacopsylla melanoneura. The genus Cacopsylla contains both transmitters and non-transmitters of phytoplasma, and transmission efficiency is not necessarily species-specific, that is, within a species, some geographic variants can transmit phytoplasmas, while others cannot. In detail, C. melanoneura, assumed to be the main vector of AP phytoplasma in Northwestern Italy, but is a poor transmitter in Northern Italy and other parts of Europe. In contrast, C. picta is the primary vector in most European populations with variable transmission rates among populations. Other occurring Cacopsylla species do not transmit phytoplasmas. Knowledge about factors influencing the transmission efficiency of ‘Ca. P. mali’ is currently scarce.
We aim to address the question of what causes different phytoplasma transmission efficiencies. We propose to use, for the first time, population genomic tools to study the tripartite interaction between the phytoplasma, the vector, and its microbiome. Specifically, we will perform: 1) genome sequencing and characterization of various vector populations; 2) genome characterization of the ‘Ca. P. mali’ strains carried by these populations, and 3) comparative genome sequencing of various endosymbionts present in the vector populations. Our goal is to determine key factors affecting transmission and test transmission efficiency directly via in vivo acquisition trials. We shall determine if AP acquisition and transmission depends on the genotype of the insect vector, on the vector's microbial community, and/or on the phytoplasma strain. Our results will provide novel insights into the complex biology of ‘Ca. P. mali’ transmission and will be therefore an important milestone in combatting this disease.

Keywords
Plant protection; Agricultural biotechnology;
Endosymbionts; Genome; Microbiome; Phytoplasma; Psyllidae;
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