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• W32362479 abstract "109 bacterial and 19 fungal antagonists of Leptosphaeria maculans (Anamorph Phoma lingam), the causal agent of blackleg on oilseed rape, were isolated from compost and rhizosphere of different crops. 58 of the bacterial isolates inhibited the mycelial growth of L. maculans and Verticllium longisporum on different nutrient media. Most of the antagonists were active against further important pathogens on oilseed rape, wheat and sugar beet. A few isolates had been excluded from the following experiments because of their broad antibacterial activity. The isolates had been characterised according to their morphological and physiological properties in order to exclude human- and phytopathogenic bacteria. Some of the isolates were identified as Pseudomonas fluorescens, Serratia plymuthica, Paenibacillus polymyxaand Bacillus circulans using the commercial test kits API and Biolog. Eighteen of the isolated antagonists and three strains obtained from the Institute of Plant Pathology and Plant Protection, University of Goettingen, were chosen for ad planta pre-screenings in the greenhouse. Production of siderophores on CAS (35 positive isolates) as well as high chitinase- and ß-1,3-glucanase activity were used as selection criteria. In addition, antagonistic activity of the twenty-one strains was checked on nutrient-poor straw extract agar, and under low temperature of 8 °C. All bacteria chosen inhibited the growth of L. maculans markedly. Colonization of rape seedlings was more effective when the seeds were treated with fluorescent pseudomonads and Serratia plymuthica compared to the applications with bacillus strains. 20 of the 21 isolates reduced the infection of rape cotyledons with L. maculans (up to 21 dpi) when cotyledons were inoculated with a spore suspension of L. maculans 6-8 days after emergence of seedlings. Cotyledon infection decreased by 73% using Ps. fluorescens Gö2I and by 50% with Ps. fluorescens RII2 and KAR1, Paenibacillus polymxya HA3e, and B. circulans KOM1 and KOM19, respectively. Based on these results, 8 isolates were selected and tested for their efficacy to reduce infection on young plants by L. maculans at growth stage BBCH14/15. To mimic the conditions of a natural infection, a method was developed where plants were inoculated with pycnidiospores and ascospores without any mechanical wounding. The antagonists were applied as a suspension (109 cfu/ml) on the root collar region and stem base of the plants, followed by inoculation with a pycnidiospore-suspension (107/ml) two days later. The infection was quantified 49 dpi by means of an ELISA (Enzyme-Linked Immunosorbent Assay). From the 8 isolates tested, Paenibacillus polymxya HA3e, Ps. fluorescens RII2 and B. circulans Kom19 showed high antagonistic activity. A combined application of HA3e and RII2 reduced infection of plants by 85.9%. This was a 32.8 to 43.6% increase in efficacy compared to the single application of the two isolates. Invasion within the root collar and stem base by L. maculans was studied with the help of a DAS-ELISA. Results suggested the lack of systemic spread of the pathogen within the host plant. When plants were highly infected, L. maculans was found above and below the stem base and root collar region in a limited radius of 5 cm apart from point of infection. This area was used to quantify the extent of infection. The susceptible variety Cobra was used to study the effect of fungal infection on seed production on single plant basis. A higher correlation was calculated between yield reduction and extent of infection (r = -0,7159; p = 0,01). A yield reduction of 28.3% and 3.3% was estimated for a severe and slight infection respectively. The effect on plant growth promotion was negligible when the root collar and stem base region were treated with suspensions of Ps. fluorescens RII2 and Paenibacillus polymxa HA3e. However, phytotoxic effects were observed when seedling roots were dipped in a suspension of 5 x 109 cfu/ml of both antagonists for one hour. The production of the antibiotics 2,4-diacetylphloroglucinol (Phl) and pyrrolnitrin by Ps. fluorescens RII2 was verified using HPLC-analysis, while colorimetric tests proved the production of HCN und IAA (>1µg/ml). Concentrations of pyrrolnitrin as low as 2ppm were effective against L. maculans in disc-assay. Colonization of antagonists on the surface of root collar and stem base was visualized by means of a cryo-REM (Raster Electron Microscope) two days after the plants were treated with a xanthan-suspension of the bacteria. But only a faint population density of Ps. fluorescens R2II and Paenibacillus polymxya HA3e could establish on the outer surface of plants above ground." @default.
• W32362479 created "2016-06-24" @default.
• W32362479 creator A5066364830 @default.
• W32362479 date "2022-02-20" @default.
• W32362479 modified "2023-10-14" @default.
• W32362479 title "Untersuchungen zum Infektionsmodus, immunologischen Nachweis und zur biologischen Bekämpfung von Leptosphaeria maculans (Desm) Ces. & de Not., dem Erreger der Wurzelhals- und Stängelfäule an Winterraps (Brassica napus L.)" @default.
• W32362479 doi "https://doi.org/10.53846/goediss-1787" @default.
• W32362479 hasPublicationYear "2022" @default.
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