Browsing by Subject "Hopfen"

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Bedarfsgerechte Stickstoffernährung von Hopfen (Humulus lupulus L.) durch Düngesysteme mit Fertigation
(2021) Stampfl, Johannes; Ebertseder, Thomas
In terms of quantity, nitrogen is the most important and most yield limiting plant nutrient in hops (Humulus lupulus L.), whereby excess nitrogen not taken up by the hop plant is subject to various loss processes. Despite that, little is known about the exact effects of an N supply varying in rate and timing for the hop varieties and cultivation systems currently used in the Hallertau, the worlds most important hop-growing region. In the Hallertau, the required amount of nitrogen is largely supplied by surface spreading of granulated N fertilizers, whereas in semi-arid growing regions, high proportions are applied via irrigation water (fertigation). The aim of this thesis was to examine nitrogen fertilization systems with fertigation under the conditions in the Hallertau region with regard to a nitrogen nutrition that is based on the hop plant’s needs. Therefore, four research questions with different sub-aspects have been formulated, as explained below. From 2017 to 2019 the experimental research and the acquisition of empirical data has been conducted in various field trials consisting of three trial series examining the most important hop varieties at different locations. Apart from a variation in rate and timing of N fertilization, different fertilizer application forms (surface application of granulated fertilizer and above- or below-ground fertigation) have also been examined. In addition to the determination of yield, quality and N-uptake at the time of harvest, further analysis methods such as the 15N-Tracer-Technique, chlorophyll value measurements (SPAD-Meter) or passive reflection measurements were used in individual field trials to depict the N-uptake and N-distribution in different parts of the plant. a) Which effects have different nitrogen treatments varied in rate and timing? These studies found that the hop plant absorbs more than two thirds of the total amount of nitrogen over a period of 7 to 8 weeks between early June and end of July - during formation of main biomass. Despite the fact that only a low amount of nitrogen is accumulated in the plant prior to this stage, the varieties Perle and Tradition showed that a nitrogen deficit in early growth stages until end of May already leads to a decrease of yield potential. This is due to a change in the variety-characteristic formation of lateral shoots (side arms) - the later the application of nitrogen, the greater the formation of side arms was reduced, starting from the bottom to higher plant sections. Consequently, a nitrogen fertilization solely based on the hop plant’s N uptake curve cannot be recommended, neither regarding yield formation nor nitrogen utilization. Instead, an early application of the first nitrogen treatment in April is of vital importance for early maturing varieties such as Perle and Tradition. Late maturing varieties like Herkules show a higher potential of compensation due to prolonged growth phases which enables a higher adaption of N-Fertilization to the plant’s N uptake curve. The ideal amount of nitrogen fertilization with regard to yield optimization has been determined by the growth pattern - depending on variety, weather conditions and location - and therefore by the N uptake, the supply of mineral nitrogen in the soil as well as the location-specific N mineralization potential. A reduction of the nitrogen fertilization to a level significantly below the plant’s N uptake not necessarily led to a limitation of biomass and yield formation in the same year, however, it resulted in an accelerated ripening and a negative impact on external cone quality. Furthermore, it showed that the storage of nitrogen in specific storage roots declines if N levels are significantly reduced, leading to lower vitality as well as limited plant development and yield formation in the following year. With regard to the hop plant’s perennial properties as well as the goal to achieve a demand-oriented nitrogen nutrition of the hop plant it is also necessary to supply the storage roots with enough nitrogen. With respect to valuable contents of alpha acid it has been found that high N supply levels during the stage of alpha acid synthesis (starting from early August) can result in a reduction of alpha acid concentration in the variety Herkules. This decrease can be caused by late and excessive N fertilization as well as by high mineral N contents in the soil. However, this effect has not been observed in the aroma varieties Perle and Tradition. b) Is it possible to determine the current nitrogen nutritional status through non-invasive methods? The measurement of the chlorophyll value with a SPAD-Meter on the lower leaves of the main shoot generally reflected the N content and N supply status of the hop plant. However, short-term changes in the N nutritional status could not be recorded with sufficient accuracy at this measuring point, especially not during the stage of main biomass formation, since increased proportions of the applied nitrogen were transported to higher plant sections, as was shown by the use of 15N. Regarding the determination of threshold values a classification of the plant development into before, during and after main biomass formation independent of the measuring point, is considered appropriate, since the chlorophyll value correlates with the plant’s development stage. Vegetation indices, calculated on the basis of reflectance spectra, represent not only the N content but also the actual N uptake of the crop, which is why passive reflectance measurement methods have a higher informative value with regard to the current N supply status of the plant compared to chlorophyll value measurements. Therefore, this technology could be used to achieve a site-specific optimization of rate and timing of N fertilization and thus a more demand-oriented nitrogen nutrition of the hop plant in the future. c) What are the effects of surface and subsurface drip irrigation? In the period from 2017 to 2019, additional irrigation of the aroma variety Perle on sandy soil led to a stabilization of the agronomic parameters cone yield and alpha acid content every year. In addition, irrigation also achieved an improvement of nitrogen utilization. Compared to subsurface systems, surface drip irrigation achieved a higher efficiency if the horizontal water distribution was limited by hydraulic soil properties. It was shown that this is due to the fact that the majority of the hop plant’s fine root system is located in the hill formed along the hop rows and the soil layers beneath it. d) What are the effects of a nitrogen nutrition via irrigation water? A system comparison was made between N fertilization systems with fertigation and a solely granulated N application. The use of fertigation resulted not only in an improvement of cone yield and alpha acid content, but also in an increase of the plants nitrogen uptake and a reduction of Nmin content in the soil, which is also associated with a reduction of the risk of nitrate leaching into the groundwater. Fertilization systems with fertigation achieved a higher nitrogen utilization especially at low N-fertilization rates. If two thirds of the total amount of nitrogen were applied via irrigation water, the concentration over a 6-week period proved to have a positive impact on all analyzed varieties, especially under conditions of a limited N supply, since a higher proportion of N has been applied during main biomass formation and the stage of lateral shoot growth. For an efficient N-fertilization with fertigation the application should take place between mid-June and late July while no significant amounts of nitrogen should be applied after early August. For early maturing varieties such as Perle and Tradition, there is a risk of a late N application as it is hardly possible to lay out the drip tubes before the 25th week of the year. Therefore, in early maturing varieties, a higher proportion of N should be applied in earlier growth stages while the amount of N applied via fertigation should be less than two-thirds of the total amount of N fertilizer. A substantial advantage of fertilization systems with fertigation is that nitrogen applied via the irrigation water is immediately absorbed by the plants, which allows an effective short-term intervention in the plant’s nitrogen nutrition. On the basis of a reliable recording of the current N supply status with sensors during the main growth stage, fertigation could be used to adjust the N fertilization in order to achieve a site-specific and demand-oriented nitrogen nutrition of the hop plant.
Metabolic engineering of flavonoid biosynthesis in hop (Humulus lupulus L.) for enhancing the production of pharmaceutically active secondary metabolites
(2012) Gatica Arias, Andres Mauricio; Weber, Gerd
For a long time, hop (Humulus lupulus L.) has been used in the brewing industry as flavoring and preserving agent. Moreover, the hop plant has been used for medicinal purposes. Recently, xanthohumol and desmethylxanthohumol have received special attention due to their potential cancer chemopreventive properties. Hop breeding programs have been mainly focused on the development of new cultivars with a high content of α- and β-acids in order to satisfy the demand of the brewing industry. However, due to the medical and pharmaceutical importance of hops, new breeding efforts have been done to create new cultivars with a higher content of xanthohumol and desmethylxanthohumol. In order, to complement these efforts, metabolic engineering of flavonoid biosynthesis offers tremendous potential to modify the production of these compounds. The flavonoid biosynthetic pathway has been intensively studied in plants. Often single target genes are regulated by several transcription factors. The R2R3 MYB transcription factor family plays an important role in the regulation of the biosynthesis of phenylpropanoids and flavonoids. Ectopic expression of these transcription factors in transgenic plants stimulated the production and enhanced the quantity of flavonoids. The main objective of the research presented here was to modulate the production of pharmaceutical metabolites in hop through metabolic engineering of the flavonoid biosynthesis pathway. Towards this goal, in a first approach, genetic engineering of hop cv. Tettnanger with the heterologous transcription factor PAP1/AtMYB75 from Arabidopsis thaliana L. was successfully accomplished. It was shown that PAP1/AtMYB75 was stably incorporated and expressed in the hop genome. The transgenic events showed reddish to pink female flowers and cones. Moreover, compared to the wildtype plants, the expression of the structural genes CHS_H1, CHI, and F3´H was elevated in transgenic hop plants. In addition, the production of anthocyanins, rutin, isoquercitin, kaempferol-7-O-glucoside, kaempferol-7-O-glucoside-malonate, desmethylxanthohumol, xanthohumol, α-acids, and β-acids in transgenic hop plants was influenced by the PAP1/AtMYB75 transcription factor. In a second approach, the homologous transcription factor HlMYB3 from H. lupulus L. was genetically introduced and expressed in the hop genome. The effect of the over-expression of the transgene on the expression rate of structural flavonoid and phloroglucinol biosynthetic genes, like PAL, C4H, 4CL, CHS_H1, CHI, F3H, F3´H, FLS, F3´5´H, OMT1, HlPT1, and VPS was examined. Transgenic events with an elevated expression of genes of flavonoid and phloroglucinol biosynthesis were identified. For quite some time successful plant tissue culture and Agrobacterium tumefaciens-mediated transformation procedures are available to genetically modify hop. However, these procedures are characterized by the low regeneration and transformation rates. Moreover, A. tumefaciens-mediated transformation is a laborious and time consuming process. For that reason, in order to evaluate further homologous or heterologous transcription factors with respect to the regulation of flavonoid and phloroglucinol biosynthesis in hop was highly desirable to have a simple and fast transformation system. A. rhizogenes-mediated transformation represents an alternative to express genes in hairy roots. Therefore, hop explants were genetically transformed with A. rhizogenes strains K599 and 15834. Hairy roots were only induced by A. rhizogenes 15834. The transgenity of the obtained hairy roots was confirmed by histochemical GUS assay. The integration of rolC and mgfp5 genes in transgenic hairy roots was confirmed by PCR. Particle bombardment combined with the regeneration of plants in temporary immersion bioreactors could provide another alternative for hop genetic transformation. In this study, a protocol for the micropropagation and shoot induction from organogenic calli of hop cv. Tettnanger using the temporary immersion bioreactors was developed. Furthermore, a procedure for particle bombardment was established using the following parameters: helium pressure of 900 psi, and target distance of 6 cm. The importance of hop relies on the secondary metabolites contain in the lupulin glands of the female cones. The present thesis demonstrated that the production of these secondary metabolites in transgenic hop plants could be influenced and enhanced by the expression of homologous or heterologous transcription factors. Moreover, the new developed transformation methods open the possibility for evaluating further genes that might influence the composition of secondary metabolites in the lupulin glands of hop.
Resistenz von Hopfen, Humulus lupulus L., gegen die Hopfenblattlaus, Phorodon humuli (Schrank)
(2010) Kryvynets, Oleg; Zebitz, Claus P. W.
Non-chemical methods controlling the damson-hop aphid, Phorodon humuli (Schrank) have recently gained importance, due to its great economical relevance and increasing problems with its chemical control. Breeding for the classic 'Genetically controlled resistance', where the plant exerts negative influence on the pest's behaviour during feeding, in this case appears as the only promising method because so far no other efficient biological control methods are available. In order to analyse the host-parasite relationship between hop and damson-hop aphid, and to provide a reliable, standardised screening method based on line-specific host selection behaviour, 1. the composition of the aphid's food, 2. hardness of hop tissue, 3. host selection behaviour and 4. parameters of aphid growth and development were investigated. In the apoplast (Intercellular washing fluid) of leaves and cones from all hop lines resveratrol was found, which also indicates an accumulation of its glycosidic form in the plant tissue. In contrast, no resveratrol could be found in samples of non-transgenic hop. An analysis for bitter acids detected alpha- and beta-acids in the cones only, not however in the intercellular space of the leaves. In a comparative study of plant tissues the contents of lupulones in leaf extracts from transgenic plants (except Tk160 and Tk424) was lower, the contents of humulones higher compared with those from non-transgenic plants. Generally leaf extracts showed higher contents of alpha- than of beta-acids. Resveratrol was not found in any of the leaf- or cone-extracts. Tissue hardness differed between transgenic and non-transgenic plants as well as between those from the glasshouse and from open land. In the field-grown plants it was definitely higher. Leaves of transgenic lines were harder than those of non-transgenic ones. This difference was pronounced particularly in young leaves. Significant differences were observed among parameters of aphid growth and development. The individual transgenic lines exert significantly different influence on P. humuli in respect of relative growth rate of individuals, rate of population increase and fecundity. There was no significant difference between the variants regarding the parameters rDS-value, life span and number of embryos. Host selection behaviour was different on transgenic versus non-transgenic plants. On leaves of transgenic plants a slowing down of food intake from the phloem and an extension of water intake from the xylem were observed. On the cones no similar effect ? general reduction or extension of intake from phloem or xylem in comparison to non-transgenic plants ? could be ascertained. Generally a strong decrease in food intake from the phloem of cones compared to that of the leaves was observed, caused by frequent phases of aphid inactivity on cones. Aphid behaviour on artificial diets was definitely influenced by different concentrations of bitter acids and resveratrol. A gradual increase in bitter acid concentration first prolonged or raised some EPG-parameters and then shortened or reduced them subsequently. This means that the aphids first reacted negatively, from a certain concentration of bitter acids on, however, positively to these substances. A raise in resveratrol concentrations led in the whole course either to a notable increase or decrease of values for the individual EPG-parameters. This suggests a xenobiotic resistance effected by this substance. Correlations between the experimental data showed the following dependencies: The humulones and lupulones found in intercellular washing fluid and in tissue extracts influence EPG-parameters that indicate factors located in the mesophyll. The duration of those phases of the penetration that take place in the intercellular space is reduced with increasing concentrations of humulones and lupulones. Food quality and quantity in plants from the glasshouse had no negative effects on the damson-hop aphid. On field-grown plants different effects of alpha- and beta-acids in the extracts on the aphids were ascertained. The contents of lupulones in cone- and leaf-extracts exerted a more inhibiting, the humulones a more promotional effect on the aphids during feeding. As with the overall contents of humulone and lupulone a different influence of individual bitter acids on aphid behaviour was recognisable in EPG-parameters. On cones the strong behaviour modification by the examined substances took effect on the mesophyll level and in the phloem. Positive correlations between the adult weight of the aphids as well as the amount of offspring per life span per insect and the bitter acid contents indicate an influence in favour of the insect. Negative correlations between the rm -value and the bitter acid contents, however, show an influence on the aphids in favour of the plant. Higher bitter acid concentrations reduce the development rate of aphid populations. Notable differences between transgenic and non-transgenic plants as well as varying effects of examined substances on the aphids, partly favourable for the plant, partly favourable for the pest, were found. These differences were partially clarified by comparing the effects of the substances when administered with artificial diets. The exact mode of action of resveratrol and its derivatives in transgenic hop lines on the damson-hop aphid requires further examination. A direct toxic effect on the aphids is very probable. As a conclusion from the clustering by examined parameters the transgenic hop line Tk424 can be designated as optimal.