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ERWINIA
Induction of pathogen resistance in fruit trees by transiently altering the flavonoid metabolism with specific enzyme inhibitors

Apple and pear trees, treated with the plant growth regulator prohexadione-Ca, are significantly less affected by fire blight (a bacterial disease), and by scab (caused by a fungus). Initial results indicate that prohexadione-Ca, which is inactive as a bactericide or fungicide, transiently alters the spectrum of endogenous flavonoids and related substances, thereby inducing natural resistance. This project aims to provide an in-depth explanation of the underlying physiological, biochemical and molecular biological mechanisms. As a result, optimised methods for fire blight control, which are urgently needed, particularly in pear-growing areas, will become available. The disputed use of antibiotics to combat this disease will no longer be required. Likewise, the understanding of the new type of resistance mechanism will lead to new, efficient, safe and environment-friendly products for pathogen control in several other crop plants.

Objectives
The following objectives are dealt with in this project:
1) chemical, biochemical and molecular clarification of the basic flavonoid pathway in apple and pear shoot tissues, its modulation after pathogen infection and after prohexadione-Ca treatment. This involves the isolation and identification of flavonoids and phenylpropanoids, the characterisation of the involved enzymes, the isolation of the respective genes as well as studies on gene expression
2) identification of the substance or combination of substances, which represent the active principle. Evaluation of the potential biological activity of bacterial endotoxin(s) versus Erwinia amylovora in vitro and in planta
3) Determination of the dynamics of fire blight and scab infections in pear and apple as related to dioxygenase inhibitor(s) application
4) Identification of additional compounds influencing flavonoid enzyme activity and evaluation of their effects on plant resistance
5) Optimisation of practical application (formulation, dosage, timing) of dioxygenase inhibitors and active resistance principles.

Progress to Date
The main deliverables and milestones have been achieved and the project ended in April 2003. Dissemination of the results is ongoing.

Results
The outcome of the project can be summarised in three different categories:
1) basic prerequisites for the investigations of the flavonoid metabolism in Rosaceous species. Standard enzyme assays are available for the main flavonoid enzymes in apple, pear, rose and hawthorn.
2) scientific knowledge. The multidisciplinary investigations of the flavonoid pathway opened the way to an alternative and environmentally safe method for resistance induction in pome fruit trees, and this approach could be transferred to other crop plants as a general protection strategy.
3) commercial product. BASF has started to commercialise prohexadione-Ca as an agent to control fire blight in pome fruit trees in various European countries.

Classified in ARABLE CROPS, FRUIT, CROP PESTS AND DISEASES

Scientist responsible for the project

Ao. Univ. Prof. KARL STICH
GETREIDEMARKT 9/173
1060 Wien
Austria - AT

Phone: +43 1588 0117320
Fax: +43 1588 0117399
E-mail: kstich@mail.zserv.tuwien.ac.at

References

Project ID QLRT-1999-01583
Organisation TU WIEN
Area 5.1.1
Start date 01 February 2000
Duration (months) 39
Total cost 1 945 369 €
Total EC contribution   1 498 885 €
Status Completed
Web address of the project   http://www.weihenstephan.de/ob/fireblight/

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