Partenaires et organisations internationales
(Anglais)
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AT, CY, CZ, DK, FR, DE, EL, IT, LV, NL, NO, PL, PT, SK, ES, CH, UK
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Résumé des résultats (Abstract)
(Anglais)
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Pandora neoaphidis (Entomophthorales) is one of the most important fungal pathogen of aphids and it has a great potential for use in biological control of aphids. As cultivation and subsequent direct application of this fungus has proven difficult, conservation biocontrol strategies are favored to control aphids. However, profound knowledge on the life cycle of P. neoaphidis, particularly its overwintering strategy, as well as its dissemination in spring is critical for the successful implementation of such strategies. Our hypothesis was that natural areas may play an important role for the winter survival and the initial population build up of P. neoaphidis in spring. Further, our hypothesis was that these early P. neoaphidis populations migrate together with the aphids from natural areas to arable crops, where the fungus may control the aphids. To test these hypotheses we have chosen two approaches. In the first approach, we intended to develop molecular markers to assess the genetic structure of P. neoaphidis populations in different aphid species, in natural habitats, and in arable land to test whether these populations truly migrate between habitats. Our goal was to develop and apply microsatellite markers. However, even though 21 microsatellite loci have been identified, no polymorphisms between different P. neoaphidis strains were detected. In the second approach, we have investigated the overwintering strategy of P. neoaphidis. To do so, we have developed a cultivation-independent PCR-based diagnostic tool. This tool allowed for detection of P. neoaphidis DNA in top soil samples collected in 2004/2005 from a nettle field harboring infected aphids in fall 2004. The results suggested an overwintering stage of P. neoaphidis in top soil layers. However, PCR-based detection methods do not provide information on the viability or the virulence of P. neoaphidis. Therefore, a field study was initiated in summer 2006 and will last until spring 2007. It aims at investigating the winter survival of P. neoaphidis in top soil layers and to test whether P. neoaphidis material detected with the PCR-based tool represents infectious fungal material. For this purpose, molecular analyses of soil samples are accompanied with a bioassay in which aphids are placed on soil samples and P. neoaphidis infection is monitored, and recorded as aphid mortality. Soil plots were artificially inoculated with P. neoaphidis in October 2006 and samples were/are being collected at different time points between October 2006 and April 2007. Preliminary results indicate a good correlation between bioassay data and PCR-based data, and suggest a decrease of P. neoaphidis inoculum present in soil after winter begins. Analysis of samples collected in April 2007 will allow to determine whether infectious fungal material is able to overwinter in top soil.
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