Conclusion
In the three investigated fruit crops the infection with specific
phytoplasmas induced different morphological and physiological responses
in the particular host plants. As apple trees generally survive a
phytoplasma infection more often and much longer than peach and pear,
some unique apple-specific responses are most interesting and indicative
features that could explain how a plant might become tolerant against
phytoplasma. Based on the results obtained, the long-lasting changes in
the structure of the vascular system with all physiological consequences
on the sap flow found in apple trees provides a promising step towards a
deeper understanding of host plant defence against phytoplasma. Despite
the growing understanding of this pathosystem, it seems clear that the
complexity of these interactions is not fully elucidated, yet, and many
open questions remain: Does the plant perceive a phytoplasma infection
at all? If so, what does the plant recognize? Is there a
MAMP/DAMP/effector present that induces an increased defence response in
the SEs? What are the specific events during infections in the host on
spatio-temporal and intensity level? How do the antagonists interact on
the molecular level? All these questions require more investigations on
the molecular level including for example RNAseq and transgenic
approaches.
Acknowledgements: We thank Sebastian Faus and Katharina
Piwowarczyk (JKI, Dossenheim, Germany) for excellent assistance in the
laboratory. We thank Felix Hergenhahn (JKI, Dossenheim, Germany) for
grafting and cultivation of the plants. We thank Andrea Lehr (MPI for
Chemical Ecology, Jena, Germany) for technical support. We are grateful
to Dr. Eva Gross (Schriesheim, Germany) for language editing. This work
was supported by the Deutsche Forschungsgemeinschaft (Grant FU 969/2-1).
Jannicke Gallinger was supported by a fund of the âLandwirtschaftliche
Rentenbankâ number 28RF4IP008.