Partner und Internationale Organisationen
(Englisch)
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B, CH, CRO, D, DK, E, F, H, I, N, NL, S, SK, UK
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Abstract
(Englisch)
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The activities of this project started in 1993 with participants from five countries who decided to adopt a biological control strategy that we now call the 'system management approach' (Müller-Schärer & Frantzen, 1996). This is a new approach of biological weed control characterised by the use of native pathogens as a relatively small inoculum. Relating disease epidemics to crop-weed interactions at the population level became the major research issue of this working group (Müller-Schärer & Frantzen, 1996; Frantzen & Müller-Schärer, 1998). As a contribution to the development of the system management approach, this research focuses less on the application of biological weed control in practice and more on scientific questions generated by developing the system management approach. The philosophy behind the research activities is described by Frantzen and Hatcher (1997). The rust fungus Puccinia lagenophorae, the selected biological control agent has been intensively studied in the past with regard to its impact on S. vulgaris (Paul et al., 1993). Further studies investigated the survival of the rust over-winter (Frantzen & Müller-Schärer, 1999), mechanisms of avoidance (Frantzen & Müller-Schärer, unpubl. obs.), and the mechanisms of resistance (Wyss & Müller-Schärer, 1999). Ongoing unpublished research concerns the effects of temperature on the infection process and seed germination. Weed population dynamics, genetic variation, phenotypic plasticity, intraspecific and interspecific competition are all being studied at present by our group at Fribourg (CH). Developing epidemics in the field implies that biotic and abiotic factors may influence both the speed of epidemic spread and the subsequent impact of P. lagenophorae on S. vulgaris. Insects are abundant in the field and may be a biotic factor influencing biological weed control. The interactions between insects and rust have been investigated (Tinney et al., 1999a; Tinney et al., 1999b) but the results have not yet been evaluated with respect to the system management approach of biological weed control. The effects of the abiotic factor temperature on P. lagenophorae epidemics are currently under investigation. A preliminary result is that the velocity of epidemic spread increases linearly with temperature in the range of 10 - 22°C (Kolnaar, unpubl. obs.). The effects of herbicides on the infection process are also investigated and preliminary results suggest that herbicides have a negative effect on P. lagenophorae epidemics (Rossi and Wyss, unpubl. obs.). Estimates of basic parameters of epidemiological models allow the calculation of velocities of epidemic spread which are presently being tested in field experiments. The impact of induced epidemics on celeriac (Apium graveolens L. var. rapaceum cv. Kojak - S. vulgaris interactions will be quantified in future field experiments.
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