Core Facility Hohenheim

Permanent URI for this collectionhttps://hohpublica.uni-hohenheim.de/handle/123456789/16626

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Comparison of floral traits in Calibrachoa cultivars and assessment of their impacts on attractiveness to flower-visiting insects
(2021) Marquardt, Melanie; Kienbaum, Lydia; Losert, Dominik; Kretschmer, Lea Annina; Rigling, Marina; Zhang, Yanyan; Schweikert, Karsten; Westermann, Nils; Ruttensperger, Ute; Rosenkranz, Peter
Ornamental plants are appreciated by humans for their colorfulness, beauty, abundant flowering and long blooming periods. Many ornamental plants can also constitute an additional foraging resource for flower-visiting insects. However, the ability of the popular ornamental plant Calibrachoa to support urban insect communities is not well documented. In this study, 20 different Calibrachoa cultivars were selected and tested in regard to their insect friendliness based on standardized observations (I) in flight tents using the large earth bumble bee Bombus terrestris as a model species and (II) in open field trials. To investigate what floral characteristics might constitute attractiveness to bumble bees, various floral traits were recorded and compared across all tested Calibrachoa cultivars. Over a two-year period, a total of 6,327 foraging bumble bees were recorded in the tent observations. In the open field observations, we counted 4,188 flower-visiting insects. Our results revealed that (I) all Calibrachoa cultivars were visited by insects for foraging, (II) the number of insect visitors varied significantly among the 20 tested cultivars and (III) the cultivars displayed different floral traits. For the morphometric floral traits and the aroma profiles of Calibrachoa, only the mean nectar quantity and a few identified compounds could be correlated with attractiveness to the model species B. terrestris. We also found that the petal color of the tested cultivars had a significant impact on the number of visitors. Therefore, B. terrestris clearly preferred red or blue Calibrachoa cultivars over those with other petal colors. However, as the cultivar preferences in the different insect groups differed, it is highly recommended to use various cultivars in urban plantings. Nevertheless, efforts must be made to explain what additional floral traits make Calibrachoa and other ornamental plants generally attractive to flower visitors. This information can then be used for breeding purposes to increase the insect friendliness of ornamental plants.
Diacetoxyscirpenol, a Fusarium exometabolite, prevents efficiently the incidence of the parasitic weed Striga hermonthica
(2022) Anteyi, Williams Oyifioda; Klaiber, Iris; Rasche, Frank
Background: Certain Fusarium exometabolites have been reported to inhibit seed germination of the cereal-parasitizing witchweed, Striga hermonthica , in vitro . However, it is unknown if these exometabolites will consistently prevent S. hermonthica incidence in planta . The study screened a selection of known, highly phytotoxic Fusarium exometabolites, in identifying the most potent/efficient candidate (i.e., having the greatest effect at minimal concentration) to completely hinder S. hermonthica seed germination in vitro and incidence in planta , without affecting the host crop development and yield. Results: In vitro germination assays of the tested Fusarium exometabolites (i.e., 1,4-naphthoquinone, equisetin, fusaric acid, hymeglusin, neosolaniol (Neo), T-2 toxin (T-2) and diacetoxyscirpenol (DAS)) as pre- Striga seed conditioning treatments at 1, 5, 10, 20, 50 and 100 µM, revealed that only DAS, out of all tested exometabolites, completely inhibited S. hermonthica seed germination at each concentration. It was followed by T-2 and Neo, as from 10 to 20 µM respectively. The remaining exometabolites reduced S. hermonthica seed germination as from 20 µM ( P < 0. 0001). In planta assessment (in a S. hermonthica -sorghum parasitic system) of the exometabolites at 20 µM showed that, although, none of the tested exometabolites affected sorghum aboveground dry biomass ( P > 0.05), only DAS completely prevented S. hermonthica incidence. Following a 14-d incubation of DAS in the planting soil substrate, bacterial 16S ribosomal RNA (rRNA) and fungal 18S rRNA gene copy numbers of the soil microbial community were enhanced; which coincided with complete degradation of DAS in the substrate. Metabolic footprinting revealed that the S. hermonthica mycoherbicidal agent, Fusarium oxysporum f. sp. strigae (isolates Foxy-2, FK3), did not produce DAS; a discovery that corresponded with underexpression of key genes (Tri5, Tri4) necessary for Fusarium trichothecene biosynthesis ( P < 0.0001). Conclusions: Among the tested Fusarium exometabolites, DAS exhibited the most promising herbicidal potential against S. hermonthica . Thus, it could serve as a new biocontrol agent for efficient S. hermonthica management. Further examination of DAS specific mode of action against the target weed S. hermonthica at low concentrations (≤ 20 µM), as opposed to non-target soil organisms, is required.
Evaluation of the importance of ornamental plants for pollinators in urban and suburban areas in Stuttgart, Germany
(2021) Marquardt, Melanie; Kienbaum, Lydia; Kretschmer, Lea Annina; Penell, Anja; Schweikert, Karsten; Ruttensperger, Ute; Rosenkranz, Peter
Urban landscapes are often characterized by a wide range of diverse flowering plants consisting of native and exotic plants. These flower-rich habitats have proven to be particularly valuable for urban pollinating insects. However, the ability of ornamental plants in supporting urban pollinator communities is still not well documented. For this study, we established flower beds at 13 different urban testing sites, which were planted with identical sets of ornamental garden plants. The pollinator visitation patterns were then observed throughout the summer seasons. Over a two-year period, a total of 10,565 pollinators were recorded with wild bees (> 50%, excluding bumblebees) being the most abundant pollinator group. Our results revealed that (I) the assortment of ornamental plants was visited by a high number of urban pollinators for collecting pollen and nectar, and (II) the pollinator abundance and composition varied significantly within the tested ornamental plants. These differences occurred not only among plant species but to the same extent among cultivars, whereby the number of pollinators was positively correlated with number of flowering units per plant. By using a generalized linear mixed model (GLMM) and redundancy analysis (RDA) we identified further significant impacts of the two variables year and location on the insect pollinator abundance and richness. Despite of the local and yearly variations, our approach provided a good and field-applicable method to evaluate the pollinator friendliness in ornamental plants. Such tools are urgently required to validate labels like ‘bee friendly’ or ‘pollinator friendly’ used by plant breeding companies.

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