Browsing by Subject "Salat"

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Das Potenzial von Falschem Mehltau als Quelle von Omega-3-Fettsäuren für die menschliche Ernährung
(2009) Anderle, Ann-Marie; Spring, Otmar
The absolute EPA ((5Z, 8Z, 11Z, 14Z, 17Z)-eicosapentaenoic acid) contents of the downy mildews of sunflowers (Plasmopara halstedii) and lettuce (Bremia lactucae) were quantified by means of GC-FID. The EPA content in sporangia of Bremia lactucae varied between 8 to 13 mg per dry weight. As at the institute of botany a collection of genetically identical sporangia strains of Plasmopara halstedii was established, the natural variation of EPA in four genetically different sporangia strains of Plasmopara halstedii on 10 different sunflower cultivars or -lines (15 days old seedlings) was investigated. The variance in EPA between the sporangia strains (LS-13.12.05-C6, BL-11.06.02-A4z, GG-16.10.97-A25, HE-10.01.06-A8) was only low (18-25 mg EPA per g dry weight). In contrast, the specific variation of EPA in infected sunflower seedlings (Giganteus, HA 821, HA 304, RHA 265, RHA 274, PM 13, 799-2, PM 17, 803-1, DM-2) was relatively high (0,28 to 1,10 mg EPA per g dry weight). Additionally three stages (minimum, optimum, maximum) of nitrogen fertilization were tested for their influence on the EPA content in infected sunflower seedlings. Statistical analysis was carried out by the program SAS. Analysis of variance based on F-tests and multiple t-tests. The influence of hydroponic fertilization (0.1 mM, 1 mM, 5 mM) on EPA in infected sunflower seedlings was high. The nitrogen dose of 5 mM almost doubled the EPA content in infected sunflower seedlings from 1 to almost 2 mg EPA per g dry weight. However, this content is not enough (by factor 10) to serve directly for human nutrition. Therefore at last a food chain trial with Bremia lactucae- infected lettuce was carried out in a cooperation project by several institutes of the Universtiy of Hohenheim. Infected lettuce was fed to hens. The omega-3-fatty acid content per egg was almost doubled (80 to 136 mg) if 10% lettuce was given to hen´s food. The infection with EPA containing downy mildew showed no effects.
The role of soil properties and fertilization management in pathogen defense and plant microbial interactions in the rhizosphere of lettuce (Lactuca sativa L.)
(2022) Windisch, Saskia Helen; Neumann, Günter
Soil microorganisms are involved in nearly all relevant soil processes and considered as key players in agro-ecosystems. This is particularly relevant for the rhizosphere which is created by the activity of plant roots with dynamic impact on microbial communities, their diversity and activity. Both, beneficial but also pathogenic plant-microbial interactions in the rhizosphere are driven by root exudates and other root-induced modifications in rhizosphere chemistry, which are highly variable in space, time, composition and intensity. The physicochemical properties of the rhizosphere are influenced by numerous external factors including nutrient availability, biotic and abiotic stress, soil properties or plant genotypic variation but the related consequences for plant-microbial interactions and the consequences for plant performance and health status are still poorly understood. In this context the present study was initiated to investigate (i) the influence of the soil type on root exudation and the composition of the rhizosphere solution (ii) their impact on interactions with soil pathogens and beneficial rhizosphere microorganisms and (iii) the effect of long-term fertilization strategies (organic vs. mineral fertilization), using lettuce (Lactuca sativa) as a well-characterized model plant for studies on plant-microbial interactions in the rhizosphere.
Uptake of enterohemorrhagic Escherichia coli into the roots of lettuce plants
(2020) Eißenberger, Kristina; Schmidt, Herbert
Within the last 10 years, the annual numbers of human infections with enterohemorrhagic Escherichia coli (EHEC) in Germany increased by a factor of 2.4. The peak was reached during the large German outbreak in 2011. Intriguingly, the source of the outbreak was supposedly traced back to organic fenugreek sprouts. Moreover, the number of EHEC outbreaks traced back to plant-based foods, e.g. fresh produce, increased also in the United States. This trend poses a serious threat to public health as fresh produce is mostly consumed raw. Also, these observations gave rise to investigate the interactions of plants and human pathogens in more detail especially as fresh produce may be contaminated directly on the field. In the present thesis, the capability of different EHEC strains and an enteroaggregative/enterohemorrhagic E. coli (EAEC/EHEC) strain, to adhere to and to internalize into the roots of different lettuce plants was investigated. These studies conducted within the scope of this dissertation focused on different aspects of the mentioned processes, such as different bacterial strains, the bacterial genetic equipment, and different environmental conditions, such as plant variety, soil type used for plant growth, and the soil microbiota. To mimic the natural conditions as close as possible, plants were grown from unsterile plant seed in unsterile soil under greenhouse conditions. In the first publication, the overall ability of EHEC O157:H7 strain Sakai to adhere to and internalize into the roots of Valerianella locusta, also known as lamb’s lettuce, grown in diluvial sand soil was described. It was demonstrated that EHEC O157:H7 strain Sakai is indeed able to attach to and internalized into the lettuce roots under the conditions tested. Moreover, this paper shed light on potentially important intrinsic bacterial factors, i.e. genes/proteins, which are putatively involved in adherence and/or internalization. Therefore, deletion mutants lacking hcpA and/or iha, were also investigated regarding adherence to and internalization into the lamb’s lettuce roots. Both genes, coding for the major subunit of the hemorrhagic coli pilus HcpA and the adhesin Iha, respectively, are supposed to be associated with adherence and therefore called “adherence factors”. However, deletion mutants lacking one or both of these genes did not show significant differences in root attachment compared to the wild-type strain. Regarding internalization, deletion of either of these genes resulted in significantly lower numbers of internalized bacteria clearly indicating that both of these genes – or the proteins encoded by these genes – play an important role during invasion of EHEC O157:H7 strain Sakai into the roots of lamb’s lettuce. Interestingly, deletion of both genes did not result in further reduction of internalization compared to single deletion mutants. Hence, hcpA and iha encode rather internalization factors than adherence factors. Moreover, internalization does not solely depend on these two factors. The second paper focused on the influence of lettuce varieties and soil type on adherence and internalization of E. coli O104:H4 strain C227/11φcu. In this study, the lettuce varieties Valerianella locusta and Lactuca sativa, also known as lamb’s lettuce and lettuce, respectively, were both grown in two different soil types, diluvial sand (DS) and alluvial loam (AL), to address the impact of plant host and environment on bacterial attachment and invasion into lettuce roots. To approach the latter aspect in more detail, the composition of the soil microbial community was analyzed in parallel by partial 16S rRNA gene sequencing. Adherence to the roots was positively influenced by the soil type as the number of adherent E. coli O104:H4 strain C227/11φcu bacteria significantly rose by a factor of three to four when the plants were grown in DS compared to AL. However, when grown in the same type of soil, no statistically significant differences in attachment were detected between the distinct lettuce varieties. On the other hand, internalization significantly differed predominantly between the two types of lettuce. Internalization into the roots of L. sativa compared V. locusta was found to be increased by a factor of 12 upon growth in DS, and by a factor of 108 when the plants were grown in AL. Moreover, internalization into the roots of L. sativa was five-times higher in AL than in DS. Consequently, the lettuce variety significantly influences to ability of E. coli O104:H4 strain C227/11φcu to internalize into the lettuce roots, while the soil type affected bacterial invasion only at the roots of L. sativa under the conditions tested. Moreover, by microbiota analysis, the inoculated strain was found within the soil microbiota, and this analysis demonstrated that soil type, lettuce variety, and the combination of both result in large differences in the composition of the soil microbiota.