Browsing by Subject "Pollen"

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Analyzing resistance to ergot caused by Claviceps purpurea [Fr.] Tul. and alkaloid contamination in winter rye (Secale cereale L.)
(2022) Kodisch, Anna; Miedaner, Thomas
Ergot caused by Claviceps purpurea [Fr.] Tul. is one of the oldest well-known plant diseases leading already in medieval times to severe epidemic outbreaks. After the occurrence of honeydew, the characteristic ergot bodies called sclerotia are formed on the ear. These are containing toxic ergot alkaloids (EAs). Strict limits are set within the European Union. Rye (Secale cereale L.) as cross-pollinating crop is particularly vulnerable to ergot since the competitive situation of fungal spores and pollen during flowering. Nevertheless, even today the threat is real as agricultural practice is changing and screening studies revealed EAs in samples of the whole cereal value chain frequently. The aims were to establish a harmonized method to test ergot resistance and EA contamination in winter rye, to clarify major significant factors and their relevance and to reveal the suitability of one commercial ELISA test. Further, effort was paid to examine the covariation of ergot amount and EA content considering different factors because of prospective legislative changes. Genotypes showed significant variation for ergot severity and pollen-fertility restoration after natural infection as well as artificial inoculation whereas a high positive correlation could be found between both treatments. Additionally, variances of environment, general combining ability (GCA), specific combining ability (SCA), and interactions were significant. Although male pollen-fertility restoration was of utmost importance, the female component was also significant. This illustrates that apart from promising selection of high restoration ability the maternal restorability could be exploited in future breeding programs especially when a high pollen amount is already reached. A large-scale calibration study was performed to clarify the covariation of ergot severity, EA content (HPLC, ELISA) considering genotypes, locations, countries, years, and isolates. EA profile was rather stable across country-specific isolates although large differences regarding the EA content were detected. The moderate covariation between ergot severity and EA content (HPLC) indicates that a reliable prediction of the EA content based on ergot severity is not possible what can also not be explained by grouping effects of the factors. Further, EAs seem not to act as virulence factor in the infection process since EA content showed no relationship to disease severity. Additionally, the missing correlation of ELISA and HPLC leads to the conclusion that the ELISA is not an appropriate tool what can be used safely to screen samples regarding ergot in the daily life. The genetic variation of male-sterile CMS-single crosses was analysed in a special design without pollen in field and greenhouse to identify resistance mechanisms and to clarify whether ergot can be reduced in the female flower. At this, comparison of needle and spray inoculation revealed medium to high correlations illustrating that both methods were suitable for this research. Significant environment and genotype by environment interaction variances were detected. So, testing across several environments is necessary also without pollen. Further, small but significant genotypic variation and identification of one more ergot-resilient candidate revealed that selection of female lines could be promising to further reduce ergot. The EA content was lower for less susceptible genotypes. Thus, EA content can be considerably reduced by breeding. A strong positive correlation could be found for ergot severity and EA content when analysing 15 factorial single crosses. The male pollen-fertility restoration was also here the most relevant component but the female component contributed an obviously higher proportion for the EA content than for ergot severity. In conclusion, this thesis demonstrate that implementing of a high and environmental stable male fertility restoration ability via exotic Rf genes can effectively reduce ergot although also the female restorability enables great opportunities. The unpredictable covariation between ergot amount and EA content illustrates that both traits have to be assessed, in particular the EA content by a valid HPLC approach to guarantee food and feed safety.
Charakterisierung der Qualität von Blütenpollen in unterschiedlichen Regionen Baden-Württembergs
(2022) Friedle, Carolin Gertrud Maria; Hasselmann, Martin
Honey bees (Apis mellifera) collect nectar and pollen from plants to feed their brood. Pollen provides a wide range of nutrients, such as proteins and lipids, but also carbohydrates, vitamins and enzymes. Because of these ingredients, pollen is also attractive to humans and is used as a dietary supplement. However, honey bees collect pollen not only from wild plants, but also from flowering crops grown in agriculture. Accordingly, contamination from plant protection products can be found in bee pollen and bee bread. In order to get a deeper insight into the occurrence and distribution of pesticide residues during an entire season, a total of 102 daily pollen samples were collected from April to July 2018 using pollen traps in an orchard in southern Germany. Almost 90% of the pollen samples showed detectable levels of pesticide residues. A total of 29 pesticides were detected in the samples, with more than half being fungicides, followed by insecticides and herbicides. Maximum concentrations of up to 4500 ng/g could be measured at the end of April. Samples collected in early May and late June also showed high levels of pesticides. A general risk management was performed to assess the risk of the detected pesticide concentrations for honey bees. The microbial quality of bee pollen is highly dependent on its botanical and geographic origin, as well as climatic conditions and post-harvest processing steps by the beekeeper. If no processing steps such as freezing or drying follow after harvest, the growth of microorganisms can be promoted and the pollen quality can be influenced by negative side effects such as fermentation or the production of mycotoxins. Bacterial and fungal colonies can be determined both by culture-dependent methods such as colony counting on plates and by culture-independent methods such as 16-rRNA amplicon sequencing. Following the hypothesis that storage conditions influence the composition of microorganisms in bee pollen, freshly harvested bee pollen was stored for seven days in June 2018 and 2019 under defined conditions (cold, room temperature, warm) and analyzed by sequencing 16S and 18S PCR amplicons. The bacterial community varied slightly between the sites studied and showed no significant difference between the storage conditions. The fungal community showed significant differences both between the studied sites and between the different storage conditions. The dominant fungal genera in the pollen samples were Cladosporium, Aspergillus and Zygosaccharomyces. While Cladosporium was most dominant in freshly collected pollen and the percentage decreased during storage, Aspergillus and Zygosaccharomyces showed a significant increase especially under warm storage conditions. Other contaminants naturally produced by plants can also have negative impacts on human health. Pyrrolizidine alkaloids belong to a group of phytochemicals, of which more than 600 structures are known in around 3% of all flowering plants worldwide. PA are known to be able to cause both acute poisoning and chronic damage or cancer in animals and humans. In July 2019, pollen was collected at 57 locations in Baden-Württemberg and analyzed for 42 different PAs and their N-oxides in order to expand knowledge about PA contamination in pollen and to be able to estimate the risk of the concentrations. A total of 22 different PAs were detected in over 90% of all samples examined. Only 5% of the PA were obtained as PA from plants of Senecio sp. identified, while 95% of PAs with a botanical background are from Echium sp. and Eupatorium sp. could be identified. The maximum total concentration of PA per sample was determined to be 48,400 ng/g. According to the risk values calculated by the BfR, however, 42% of the samples represented an increased risk to human health.
Effective pollen-fertility restoration is the basis of hybrid rye production and ergot mitigation
(2022) Miedaner, Thomas; Korzun, Viktor; Wilde, Peer
Hybrid rye breeding leads to considerably higher grain yield and a higher revenue to the farmer. The basis of hybrid seed production is the CMS-inducing Pampa (P) cytoplasm derived from an Argentinean landrace and restorer-to-fertility (Rf) genes. European sources show an oligogenic inheritance, with major and minor Rf genes, and mostly result in low-to-moderate pollen-fertility levels. This results in higher susceptibility to ergot (Claviceps purpurea) because rye pollen and ergot spores are in strong competition for the unfertilized stigma. Rf genes from non-adapted Iranian primitive rye and old Argentinean cultivars proved to be most effective. The major Rf gene in these sources was localized on chromosome 4RL, which is also a hotspot of restoration in other Triticeae. Marker-based introgression into elite rye materials led to a yield penalty and taller progenies. The Rfp1 gene of IRAN IX was fine-mapped, and two linked genes of equal effects were detected. Commercial hybrids with this gene showed a similar low ergot infection when compared with population cultivars. The task of the future is to co-adapt these exotic Rfp genes to European elite gene pools by genomic-assisted breeding.
The role of pollen as alternative food for predatory mites (Acari: Phytoseiidae)
(2018) Schreiber, Irina; Zebitz, Claus P. W.
Predatory mites of the family Phytoseiidae (order Acari) are important biological control agents of various greenhouse pests. Their successful establishment in greenhouses depends on abiotic and biotic factors, and on different adaptation levels of the different mite species, which must be considered before practical implementation. In this study, the suitability and effect of pollen as alternative food was assessed for the predato-ry mites A. swirskii, A. limonicus, and A. cucumeris (Acari, Phytoseiidae). Besides lifetable and demographic parameters, body weight and size was included into the descriptive parameters, which has not been done before to obtain more detailed information on pollen quality for these mite species. In the first study (Goleva and Zebitz 2013), the suitability of pollen of 21 plant species as alternative food for A. swirskii was tested. Preimaginal mortality and developmental time have been assessed, followed by a life-table analysis of the emerged adults and a calculation of demographic parameters. Amblyseius swirskii was able to feed on 18 pollens, but the nutritional properties of the pollen differently affected mite performance. Pollen of Lilium martagon and Hippeastrum sp. were found to be toxic for the mites, probably due to secondary plant compounds in this pollen. Amblyseius swirskii was absolutely not adapted to feed on Hibiscus syriacus because of the external morphology of pollen grains, leading also to 100 % preimaginal mortality. The best pollen resulting in superior mite performance in all parameters tested were: Aesculus hippocastanum, Crocus vernus, Echinocereus sp. and Paulownia tomentosa. No or low mortality was observed when mites fed on other pollen tested. Developmental time, adult longevity, and reproduction parameters, were significantly affected, probably because of differences in pollen nutrient or non-toxic secondary compound composition. Commercial bee pollen was of very poor quality for the mites leading to low egg production, which excludes this pollen for practical use. Pollen of Helianthus annuus, Corylus avellana and a Poaceae-mix were of inferior quality, causing high mortality rates, low egg production and short adult longevity. For practical implementation in greenhouses, pollen of Ricinus communis, Zea mays, A. hippocastanum and Betula pendula pollen appeared suitable to improve predatory mite performance, either provided by banker plants or in form of dispersible pollen. The objective of the second study (Ranabhat et al. 2014) was to assess the suitability of seven pollen (castor bean, tulip, apple, Christmas cactus, horse-chestnut, maize, and birch) for Neoseiulus cucumeris (Acari: Phytoseiidae), and to scrutinize potential effects of these pollen on reproduction and life history parameters of this mite. Neoseiulus cucumeris accepted six pollen sources as alternative food, pollen of castor bean plants, however, caused 100 % mortality. Highest fecundity was observed when feeding on pollen of tulip and horse chestnut, resulting in the shortest preimaginal development compared with all pollen tested. Pollen of birch, tulip, maize, and apple had a positive effect on longevity, whereas pollen of horse-chestnut and Christmas cactus was significantly inferior. Our study suggests that birch, tulip, horse-chestnut, apple, and maize pollen may serve as alter-native food in the field, and birch and maize pollen have a good potential in practical use as banker plants or dusts in the greenhouse to guarantee mite establishment in periods of prey scar-city. The aim of the third study (Goleva et al. 2014) was to investigate the role of pollen of differing quality (tested previously in first study (Goleva and Zebitz 2013) on size and weight of A. swirskii. These parameters were considered from the physical aspect of predator-prey relations because predatory mites are not able to conquer prey individuals bigger than themselves and any deviation from normal size may negatively affect predation success. Biomass and body size of freshly emerged, 1, 3, and 30 days old adult A. swirskii continuously reared on pollen of B. pendula, H. annuus, P. tomentosa, and Zea mays revealed, regardless of pollen source, that females were bigger than males. Both parameters weight and size were affected by pollen tested. Females fed on pollen of P. tomentosa and Z. mays were significantly bigger than on B. pendula or H. annuus pollen. Increase of female biomass was observed until the adult age of 3 days, remaining constant or slightly decreased until the age of 30 days. This can be explained by particularly high nutritional requirements of females for egg production especially in the beginning of their repro-duction period. Males also reached their weight maximum at day 3 of adult life, then decreasing until day 30. Congruent with biomass, adult body length and width differed significantly depending on sex and age showing females bigger than males and 30 day old adults bigger than 1 day old adults irrespective of the pollen fed. While sunflower pollen was of poor quality for A. swirskii, causing small size and low weight of both sexes, pollen of P. tomentosa was significantly superior in both parameters. No reasonable correlation was found between body length and width, but body weight was significantly correlated with body length in females whereas there was no correlation at all in males. In a fourth study (Goleva et al. 2015), adult body weight of the generalist mites A. swirskii, A. limonicus, and N. cucumeris reared on 22, 12, and 6 pollen species, respectively, was assessed. In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs.In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs. In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs.In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs. In all mite species, female body weight was higher than that of males.Nutritional quality of pollen was neither consistent among the mite species nor among sex, revealing superior quality of Quercus macranthera pollen for females of A. swirskii and T. gesneriana pollen for males, Alnus incana pollen for females of A. limonicus and Ae. Hippocastanum pollen for males, and Ae. Hippocastanum pollen for both sexes of N. cucumeris. Pollen affected predatory mite species in our studies in various ways. Besides lifetable parame-ters, pollen also affected adult weight and size of predatory mites and these parameters should therefore be considered additionally in future studies to obtain more exhaustive information on nutritional biology and physiology of predatory mites. The differences in the parameters assessed and the mite species performance may be explained by different adaptations of mite species to pollen compounds. Knowledge in the chemical composition of pollen, however, particularly the nutritive substances, is poor or even lacking. Any correlation of performance parameters with nutrients is more or less theoretical unless the pollen constituents are known. Even then, nutritional physiology of predatory mites and their adaptation to various food sources must be improved and include mite’s enzymatic activity to metabolize secondary plant compounds in pollen. The results presented in this thesis open the door to future research on mite nutritional biology.