Partner und Internationale Organisationen
(Englisch)
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AT, BE, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GR, HU, IE, IL, IS, IT, LT, LV, MK, NL, NO, PL, PT, RO, SE, SK, UK
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Abstract
(Englisch)
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A significant potential exists to improve beneficial effects of root colonizing bacteria by breeding wheat genotypes with a greater capacity to sustain the interactions with these bacteria. However, the interaction of crop plants and bacteria as well as the conditions which favor the accumulation of beneficial microorganisms are largely unknown. Therefore we have in a first step evaluated the abil-ity of different Swiss wheat varieties (Arina, Zinal, and Cimetta) to accumulate naturally occurring plant beneficial pseudomonads and Pseudomonas spp. containing the phlD-gene. This gene is re-sponsible for the production of the antimicrobial compound 2,4-diacetylphloroglucinol (Phl), a key factor for the disease suppressive capacity of many fluorescent pseudomonads. Our results have shown that indeed there are variety specific differences. Some varieties accumulated more total pseudomonads and some more phlD+ pseudomonads compared to other varieties. Furthermore, a significant interaction between soil origin and wheat variety in respect of root colonization by Pseu-domonas spp. was found. In a next step, we characterized the Pseudomonas spp. populations which had accumulated in the rhizosphere of the different wheat varieties grown in two different soils. To this end populations producing Phl were analyzed by studying the diversity of a Phl biosyn-thetic gene using RFLP and DGGE. In one of the soils the variety Cimetta strongly differed from the other two varieties in the general genetic diversity of phlD+ pseudomonads colonizing its roots. However, the phlD genotype which had accumulated most on the roots was the same for all three varieties. In order to investigate whether the fitness of selected varieties can be improved by bacte-rial inoculants, we tested three different wheat genotypes for their ability of being protected by the well-described Pseudomonas fluorescens strains CHA0 and KD against the soil-borne pathogen Pythium ultimum. Furthermore plant growth promotion by these bacterial strains was evaluated in absence of a pathogen. In contrast to strain CHA0 strain KD did neither suppress Pythium nor pro-mote plant growth on any variety tested. For strain CHA0 we found variety-specific differences in the ability of wheat to benefit from this bacterium. The disease suppression on Arina was significantly better compared to the other two varieties, however, Arina profited less than Zinal and Cimetta from the plant growth promoting effect of strain CHA0. The evaluation of the potential of wheat genotypes to benefit, in terms of plant health and growth, from bacterial inoculants will allow selecting for best inoculant-wheat variety combinations for the use in low-input agricultural systems. These experi-ments give a good overview of the two-way interaction plant genotype x beneficial bacteria and pro-vide essential information for breeders which allow the development of a new and unique wheat breeding strategy for low-input and organic conditions. We have observed that some wheat varieties do neither support naturally occurring beneficial pseudomonads producing antimicrobial compounds very well nor do they profit satisfactorily from inoculation with biocontrol pseudomonads producing such metabolites. Since those wheat varieties which cannot profit from antimicrobial compound pro-ducing biocontrol strains are still of great agronomical value it is of importance to find other Pseu-domonas spp. strains specially adapted to and performing well on these varieties. Therefore we have isolated from the rhizosphere of these wheat varieties new Pseudomonas spp. strains and screened them for novel biocontrol mechanism other than antibiosis. Especially one isolate P. putida strain KT2440 showed good ability to control Gaeumannomyces graminis var. tritici. The bio-control mechanisms of this strain were investigated and we could demonstrate that the bacterial degradation of nutrients essential for the G. graminis var. tritici. to infect wheat roots plays an impor-tant role in the disease suppression by KT2440.
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