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Biological control of broomrapes

Final Report Summary - BIOBROOM (Biological control of broomrapes)

Marie Curie Intra European Fellowship (IEF) No. 220177 under the title BIOBROOM was carried out at Wageningen University, the Netherlands through 2008 - 2010. The research was devoted to biological control of broomrapes (Orobanche spp.), where oligophagous agromyzid fly Phytomyza orobanchia (Agromyzidae) was a key tool. The project was focused on tritrophic aspects of the host plant selection by the fly. In order to address this problem, headspace volatiles of 21 different broomrapes as well broomrape hosts were collected. Headspace samples were analyzed using GC/MS and used for identification of Phytomyza-behaviour-effecting compounds using GC/EAD analyses and Y-tube olfactory experiments. The effectiveness of selected volatiles was tested in field experiments (in natural ecosystems). Following this outline, many exciting achievement arose. The three most important were as follows:

1. The top achievement was Phytomyza related. Key points briefly:

- the fly using scents of broomrapes for orientation;
- from among huge array of volatiles emitted by each broomrape, there are 40 mutual compounds for all broomrapes; 12 of them elicited antennal (EAG) responses; one of these compounds is unique for broomrapes;
- antennal responses for 3 compounds were very stable and also ratio between them in natural blends of all broomrapes (21 species screened) was stable;
- 5 different baits (based on GC/MS analyses) in simple delta traps yielded reasonable catch (Phytomyza adults) under field conditions; bait based on the three most EAG active compound caught 2x more flies as any other bait and the second-best bait (which contained all EAG active compounds) was as attractive as broomrape flower.

The composition of the most attractive bait will be patented. The results of this work are also expected to improve the efficacy of biological control of Orobanche spp., e.g. through positive effects of selected kairomones on the efficacy of P. orobanchia, increased attraction to its host, mass trapping and redistribution and attraction of flies to use them as vectors of disease into the broomrape population.

2. In this study, for the first time, the phylogenetic relations of parasitic plants (broomrapes) on the basis of volatile organic compounds (VOCs) emitted were investigated. VOC profiles of 21 different broomrape species (Orobanche and Phelipanche), five other parasitic plants from genera Striga, Cistanche and Cynomorium, and five closely related non-parasitic plants from genera Anthirrinum, Mimulus and Paulownia were used to create phylogenetic tree, and compared with taxonomic phylogenetic tree. Results show that the host range and life history of broomrapes evolve in correlated fashion. Besides VOCs shed more light on arrangement of some problematic broomrape species, what is hard realise using other methods. The MetAlign software was employed for the analysis, alignment and comparison of Mass Spectrometry datasets and subsequently principal component analysis (PCA) and pvclust (R package for assessing the uncertainty in hierarchical cluster analysis) for the next steps.

3. The early change in plant volatile emission and detection of de novo induced volatiles upon infection with parasitic plants (e.g. in rice or sunflower) was discovered. This knowledge could be developed into an early warning system by using sensors that can detect the difference between healthy and broomrape infected plants, such that selective herbicide application can be used.