Phytoparasitica (2002) 30 (3) - Broomrape (Orobanche spp.) as ...

D.M. Joel (2002)
Broomrape (Orobanche spp.) as an angiospermous pathogen: biological aspects and their impact on potential control
Phytoparasitica 30 (3)
The 23rd Congress of the Israeli Phytopathological Society - February 11-12, 2002
Abstract: Broomrape is a higher plant, but nevertheless exhibits many similarities with fungal pathogens, being a holoparasite that connects to host root tissues and interacts physiologically directly with the host. In this respect broomrape differs significantly from other weeds that compete only in the environment of agricultural crops and do not interfere with any exploitation of crop photosynthates. Another similarity with fungal pathogens is that it is not detected in the field during much of its development, and is discovered only after much of its damage has already been done. Contrary to other pathogens, broomrape resembles its hosts in physiological terms, and therefore selective control is tricky. Our understanding that the broomrape serves as a strong sink may help in controlling it, by using systemic herbicides that inhibit important metabolic pathways in the pathogen. Glyphosate and ALS inhibitors are thus effective in broomrape control, but are not selective to many crops. The use of transgenic crops with target-site resistance to these herbicides enables effective control of broomrape. However, these herbicides will sooner or later meet with herbicide-resistant broomrape races. Another way to reduce broomrape damage is the use of broomrape resistant crops. Sadly there are so far only very few sources of resistance, and again, new broomrape races are found that successfully attack resistant crops, thanks to the highly polymorphic nature of the parasite. The arsenal of Orobanche control methods is limited. Strict sanitation and new control methods therefore are needed for effective control of the parasite, both depending on suitable diagnostic capabilities. In order to cope with broomrapes that show different host capabilities we have developed in recent years tools for the molecular identification of all broomrape species that are known in the Mediterranean region. We have also developed the means to identify a single soilborne seed using SCAR (Sequence Characterized Amplified Repeats). Additional means to challenge the broomrape problem should include the development of artificial resistance and manipulation of key metabolic and developmental processes in the parasite. For this purpose we have carefully studied different stages in the life cycle of the parasite. For example, we found that the haustorium releases some wall-degrading enzymes during the penetration process. Penetration may be stopped once we provide the host with the ability to react to the presence of these enzymes, either by a hypersensitive reaction or by the release of a toxin. Another example is based on the understanding of seed conditioning, i.e., the developmental stage that is needed in order to render the seeds sensitive to germination stimulants, and that takes place when broomrape seeds are exposed to water. We were able to prevent parasitism by inhibition of gibberellin synthesis during seed conditioning. This was used as a model that proves that interrupting metabolic activities during seed conditioning may enable control of the parasite by preventing its germination. Other developmental stages, such as germination stimulation, are also possible targets, and the mechanisms involved may be manipulated for specific control of the parasite.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Daniel M. Joel

Research topic(s) for pests/diseases/weeds:
review
control - general

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Orobanche (weeds)