Factors influencing Phytoplasma transmission

Phytoplasmas are bacteria responsible for a wide range of plant diseases. These bacteria are transmitted by sap-sucking insects, especially jumping plant lice. Apple proliferation is a phytoplasma disease of apple trees in Europe. First described in the 1950s, two outbreaks in the late 1990s and the first decade of the 2000s have caused vast economic damages in the apple growing regions of Northern Italy. Infected plants cannot be cured. Therefore, the control of plant lice is currently the most efficient w ay to limit the spread of the disease. Two lice species are the main transmitters of Apple Proliferation: Cacopsylla picta is the main transmitter in Northern Italy and most other regions in Europe. It is absent in Northwestern Italy, where Cacopsylla melanoneura transmits the disease. Interestingly, this species is not able to transmit the disease in other regions of Europe. Knowledge about factors influencing phytoplasma transmission is scarce. In our project, we will study the interplay of three groups of organisms involved in the spread of Apple Proliferation: the phytoplasmas, the plant lice species, and other bacteria colonizing the lic e. New technologies have made it possible to read huge amount of DNA sequences at low costs. We will use such technology to characterize many genes of the phytoplasma, the plant lice, and their bacteria. We will use samples from various parts of Italy. We will search for yet undiscovered lice species and test how good they transmit phytoplasmas. Furthermore, we will test whether phytoplasma strains from different regions are identical, or if multiple strains cause Apple Proliferation. Finally, we will test if bacteria present in the insects influence phytoplasma transmission. Taken together, our study will provide novel insights into phytoplasma transmission and will contribute to the development of new methods to control the disease.

Apple Proliferation is a bacterial disease of apple trees in Europe. First described in the 1950s, this phytoplasma disease has caused vast economic damages in the apple growing regions in Europe, and particular in Northern Italy. Infected plants with this phytoplasma disease cannot be cured. Therefore, the control of the vectors, i.e. the jumping plant lices is the most efficient way to limit the spread of the disease. Two lice species are the main transmitters of Apple Proliferation in Europe: Cacopsylla picta and Cacopsylla melanoneura. Interestingly, latter species infests apple and hawthorn. In this project we analysed the genome of these two plant lices and phylogenies estimate a mid-Miocene divergence. Furthermore, data revealed that Italian samples were genetically distinct from populations in Central Europe. Results also showed a clear separation between C. melanoneura collected on apple and hawthorn, suggesting the existence of two different ecological and genetic variants within this species. While individuals from hawthorn displayed high variation compared to the variants of apple. Nevertheless, even within the apple, individuals subtle genetic differences could be observed between different populations. The data presented here provides a robust phylogenetic framework and a first genetic repository for future studies.