Institut für Kulturpflanzenwissenschaften

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A cropping system for yacon (Smallanthus sonchifolius Poepp. Endl.) : optimizing tuber formation, yield and sugar composition under European conditions
(2020) Kamp, Larissa; Graeff-Hönninger, Simone
The demand of healthy food is constantly increasing in Germany, as well as in developed countries in general. Here "healthy" is not clearly defined but it is often associated with foods indicating a low caloric value and further health-promoting benefits such as a high proportions of dietary fiber, phenols or antioxidants. In contrast, the proportion of obese people and the number of chronic diseases such as diabetes type II and obesity are increasing. As a result, the European Commission recommended to reduce the sugar content and the caloric value of food products, especially in sweetened beverages, breakfast cereals and dairy products by 10%. In general, a distinction can be made between artificial and natural sweeteners. Natural sweeteners such as honey, agave nectar or rapadura occur naturally and do not have to be artificially produced or synthesized. Disadvantages here are the high production costs as well as the high calorie value which is similar to conventionally used sugar. Artificial sweeteners, on the other hand, which are also known as "high-intensity sweeteners", have been artificially produced or synthesized. Examples are aspartame, saccharin or sucralose. They often have a lower calorie value (except for sugar alcohols such as xylitol or sorbitol) and are more economical to produce, which makes them particularly attractive for food producers. However, artificial sweeteners are suspected of being harmful to health or even carcinogenic. As a result, the consumer acceptance of artificial sweeteners is decreasing and the demand for natural sweeteners as alternatives is increasing. A possible alternative as a natural sweetener is yacon (Smallanthus sonchifolius). Yacon is a tuberous root crop native to the Andean region. The roots store carbohydrates mainly as fructooligosaccharides (FOS). These FOS cannot be digested by the human intestinal tract, and therefore do not cause a noticeable increase of blood glucose level. In addition, high amounts of fiber, phenols and antioxidants lead to further health promoting benefits. So far, yacon has been cultivated mainly in the Andean region in smallholder structures. Therefore, there are several open questions regarding the cultivation of yacon in Europe, especially in the area of propagation, choice of genotypes and adapted nitrogen fertilization. Especially the propagation is an important factor, as it is normally done by seedlings of mother plants or single rhizome pieces, both with pre-cultivation in the greenhouse. This is expensive and leads to a price of 3.60 € for young plants. In addition, the influence of genotype and amount of nitrogen fertilization on tuber yield and sugar composition has not been investigated yet. These open questions regarding the cultivation of yacon in Europe outline the following objectives: • to evaluate differences between direct planting and pre cultivation of rhizomes in two ways with regard to yacon growth, development, tuber yield formation and cost distribution; • to investigate the yield potential of different yacon genotypes with regard to tuber yield, sugar yield and tuber composition under the given climatic conditions of Europe; • to determine the influence of different nitrogen levels on nitrogen uptake, tuber yield formation and amount of monosaccharides and polysaccharides as well as total sugar; • to investigate the environmental impact and the production costs of different yacon cultivation systems to determine the most sustainable cultivation method. To achieve the objectives, field trials were carried out a from 2016 to 2018. As a result, four scientific publications were developed, which formed the body of this thesis. Publication I focused on the differences between a propagation with pre-cultivation in the greenhouse (DSAB), rhizome pieces with pre-cultivation in the greenhouse (RP1) and a direct planting of rhizome pieces (RP2) in agronomic and economic terms. RP1 achieved the highest yield with 29.8 t ha 1 FM and differed significantly from the other treatments with 21.3 and 17.8 t ha-1 FM (DSAB and RP2, respectively). With regard to the cost per kg of produced yacon, RP1 was also convincing, which can be explained by a high tuber yield and comparatively low propagation costs. DSAB was the most expensive treatment and is therefore not recommended. Contrary to that RP2 has a high potential for mechanization and yield increases. Publication II investigated the differences between nine different genotypes with respect to tuber yield and sugar composition. The three genotypes red-shelled, brown-shelled and Morado achieved the significantly highest tuber yields with 46.6, 43.5 and 41.6 t FM ha-1. Also the sugar contents were outstanding with up to 66% of the DM in the red-shelled genotype. As a result, the sugar yields of these three genotypes were highest with 2.2, 2.0 and 1.9 t ha-1 in the same order as the tuber yields. In Publication III the influence of different amounts of nitrogen fertilizer (0, 40 and 80 kg ha-1) on tuber yield, sugar composition and nitrogen uptake of the brown- and red-shelled genotype was investigated. Both genotypes reached highest tuber yields of 50 and 67 t FM ha-1 at the highest nitrogen fertilizer amount (brown- and red-shelled, respectively). Contrary to this responded the total amounts of sugar and FOS. Both decreased with increasing amounts of nitrogen. With decreasing amounts of FOS, the proportion of FOS with higher degree of polymerization (DP) increased. With regard to the nitrogen utilization efficiency of both, tubers and the entire plant, a nitrogen amount of 40 kg N ha-1 seems to be sufficient and recommendable. Publication IV examined the ecological and economic sustainability of the cultivation of two genotypes (brown- and red-shelled), each with pre-cultivation in the greenhouse and as direct planting, with three different nitrogen fertilizer levels. The aim was to investigate the environmental impact and production costs of different yacon cultivation systems. Considering the costs, the highest fertilizer amount (80 kg N ha-1) led to the lowest production costs and also to comparatively low environmental impacts per functional unit (1 kg FOS). The red-shelled genotype performed better, both in terms of cost and environmental impact. This was mainly due to higher tuber yields. Overall, the preceding publications showed that the cultivation of yacon in Europe is possible and offers new possibilities for farmers. Embedding yacon successfully into existing cropping systems and crop rotations seems to be possible. The farmer has the opportunity to establish a promising new crop with great value potential on his farm in order to cover the increasing demand for raw materials for natural sweeteners.
Acrocomia aculeata fruits from three regions in Costa Rica: An assessment of biometric parameters, oil content and oil fatty acid composition to evaluate industrial potential
(2020) Alfaro-Solís, Jose David; Montoya-Arroyo, Alexander; Jiménez, Víctor M.; Arnáez-Serrano, Elizabeth; Pérez, Jason; Vetter, Walter; Frank, Jan; Lewandowski, Iris
Due to increased global demand for vegetable oils, diversification of the supply chain with sustainable sources is necessary. Acrocomia aculeata has recently gained attention as a multi-purpose, sustainable crop for oil production. However, the information necessary for effective selection of promising varieties for agricultural production is lacking. The aim of this study was to assess variability in fruit morphology and oil composition of individual Acrocomia aculeata plants growing wild in different climatic regions of Costa Rica. Fruits at the same ripening stage were collected at three locations, and biometric features, oil content, fatty acid composition of oils from kernels and pulp, as well as fiber composition of husks were determined. Biometric parameters showed high variability among the regions assessed. Moreover, oil content and relative proportions of unsaturated fatty acids were higher at the most tropical location, whereas lauric acid content was lowest under these conditions, indicating a potential environmental effect on oil composition. Pulp oil content correlated positively with annual precipitation and relative humidity, but no clear relation to temperature was observed. The oil chemical composition was similar to that reported for Elaeis guineensis, suggesting that Acrocomia aculeata from Costa Rica may be a suitable alternative for industrial applications currently based on African palm oil. Analysis of husks as a coproduct revealed the possibility of obtaining materials with high lignin and low water and ash contents that could be used as a solid bioenergy source. In conclusion, Acrocomia aculeata oil is a promising alternative for industrial applications currently based on African palm oil and byproducts of its oil production could find additional use as a renewable energy source.
Agrarlexikon mit den wichtigsten Begriffen zur Landwirtschaft im europäischen Umfeld : Bedeutung in deutscher und englischer Sprache erklärt
(2017) Hartmann, Peter; Raupp, Manfred G.
Agricultural diversification of biogas crop cultivation
(2018) von Cossel, Moritz; Lewandowski, Iris
For all types of agricultural land-use, more diverse cropping systems are required, with respect to the maintenance of ecosystem values such as biodiversity conservation and climate change adaptation. This need for greater agricultural diversity is clearly illustrated by biogas crop cultivation. In Germany, maize currently dominates biogas crop cultivation due to its outstanding methane yield performance. However, the ecosystem value of maize cultivation decreases if good agricultural practices are ignored. Additionally, the poor aesthetical value of maize has led to biogas production gaining a negative reputation in society. To increase the diversity of biogas crop cultivation, alternative biogas crops such as amaranth and wild plant mixtures need to be investigated with respect to both yield performance and biogas substrate quality. The research objective of this study was the development of strategies for agricultural diversification of biogas crop cultivation. For this purpose, the following research questions were formulated: 1. How does amaranth perform as a biogas crop compared to maize and what are the major opportunities for and obstacles to the large-scale implementation of amaranth cultivation? 2. How does the spatial diversification ‘legume intercropping’ perform in amaranth compared to maize and what are the major opportunities for and obstacles to its practical implementation? 3. How do perennial wild plant mixtures perform in biomass production with respect to yield, quality and species diversity in the long term and what are the relevant agronomic factors? 4. How do available models perform in the prediction of specific methane yield of different crops based on their lignocellulosic biomass composition and how could they be improved? To address research questions 1 and 2, field trials with amaranth and maize were conducted in southwest Germany in the years 2014 and 2015. Amaranth established well in both years. Its dark red inflorescences attracted many insects such as honeybees, wild bees and bumble bees. Therefore, a systematic implementation of amaranth into biogas crop rotations could significantly improve their socio-ecological value in terms of biodiversity conservation and landscape beauty. However, amaranth showed significantly lower dry matter yields (DMY) and specific methane yields (SMY), together resulting in lower methane yields than maize in both years. Therefore, breeding and an optimization of agricultural practices such as sowing density, planting geometry and fertilization management are required to make amaranth more competitive in comparison to maize. To address research question 2, the amaranth field trials mentioned above also included treatments of legume intercropping with runner bean (RB, Phaseolus vulgaris L.) and white clover (WC, Trifolium repens, L.). The RB and WC developed equally well in amaranth and maize each year. For both amaranth and maize, the RB share of total DMY was low (5-10%) and did not significantly affect the total DMY. By contrast, WC had a significant negative effect on the DMY. Overall, the spatial diversification ‘legume intercropping’ could considerably improve the socio-ecological value of amaranth cultivation in terms of biodiversity conservation, greenhouse gas (GHG) mitigation and soil protection. For research question 3, two different wild plant mixtures (WPM) were cultivated on three sites in southwest Germany from the years 2011 to 2015. At each location, the WPM showed great potential for both biodiversity conservation and ecosystem resilience. Numerous insect species were observed in the WPM stands each year, indicating WPM as a relevant cropping system for habitat networking. Furthermore, the aesthetic appearance of the WPM stands over the years demonstrated the potential positive effect WPM cultivation could have on the public perception of biogas production. The DMY of the WPM varied strongly depending on (i) the initial composition of species sown, (ii) the establishment procedure, (iii) the environmental conditions, (iv) the pre-crop, and (v) the number of predominant species. WPM were found to have low demands for fertilization and crop protection. Thus, WPM appear a promising low-input cropping system for the promotion of biodiversity conservation, habitat networking, soil and water protection, GHG mitigation and climate change adaptation. However, high DMY gaps remain a challenge for the practical inclusion of WPM in existing biogas cropping systems. With respect to research question 4, a meta-analysis revealed that available models proved to be much less precise than expected. Although outperforming all available models, the correlation of the new models was still low (up to r = 0.66). It was also found that non-linear terms are of less importance than crop-specific regressors including the intercept. This indicates that across-crop models including crop-specific configurations could help to improve the identification of alternative crops and cropping systems for a more diverse biogas crop cultivation in the future.
Agriculture in responsibility for our common world
(2022) Raupp, Manfred G.; Thomas, Angelika; Schüle, Heinrich; Carabet, Alin Flavius; Salasan, Cosmin; Fora, Ciprian George; Weinmann, Markus; Madora GmbH; University of Hohenheim, Institute of Crop Science; Klara Bradacova
The vocational training course program “Agriculture in Responsibility for our common World” organised within the frame of the Banat Green Deal Project “GreenERDE” (Education and Research in the context of the digital and ecological transformation of agriculture in the Banat Region and Baden-Württemberg - towards resource efficiency and resilience) and delivered between June 2021 and May 2022 targets the knowledge and experience transfer to the farmer community in the Banat Region, Romania and other parts of the world. Current and future challenges, such as the ecological conversion and digital transformation of agricultural production, but also social, economic and cultural aspects haven been addressed transcending prevailing patterns. The innovative and relevant knowledge originating from practice, experiments, research or development projects throughout Europe and other continents is presented in a training format for interested participants.
Agrivoltaics mitigate drought effects in winter wheat
(2023) Pataczek, Lisa; Weselek, Axel; Bauerle, Andrea; Högy, Petra; Lewandowski, Iris; Zikeli, Sabine; Schweiger, Andreas
Climate change is expected to decrease water availability in many agricultural production areas around the globe. At the same time renewable energy concepts such as agrivoltaics (AV) are necessary to manage the energy transition. Several studies showed that evapotranspiration can be reduced in AV systems, resulting in increased water availability for crops. However, effects on crop performance and productivity remain unclear to date. Carbon‐13 isotopic composition (δ13C and discrimination against carbon‐13) can be used as a proxy for the effects of water availability on plant performance, integrating crop responses over the entire growing season. The aim of this study was to assess these effects via carbon isotopic composition in grains, as well as grain yield of winter wheat in an AV system in southwest Germany. Crops were cultivated over four seasons from 2016–2020 in the AV system and on an unshaded adjacent reference (REF) site. Across all seasons, average grain yield did not significantly differ between AV and REF (4.7 vs 5.2 t ha−1), with higher interannual yield stability in the AV system. However, δ13C as well as carbon‐13 isotope discrimination differed significantly across the seasons by 1‰ (AV: −29.0‰ vs REF: −28.0‰ and AV: 21.6‰ vs REF: 20.6‰) between the AV system and the REF site. These drought mitigation effects as indicated by the results of this study will become crucial for the resilience of agricultural production in the near future when drought events will become significantly more frequent and severe.
Agronomic strategies to reduce potential precursors of acrylamide formation in cereals
(2020) Stockmann, Falko; Graeff-Hönninger, Simone
Food safety is of great importance as harmful substances formed during food processing can negatively affect human health. When the carcinogenic food ingredient acrylamide (AA) accidentally appeared in 2002, it was not expected that AA would take this much attention during the next years. Yet, after around 15 years of research, AA has finally been recognized as being harmful. In a first step, research focussed on food processing implications on AA formation. The impact of heat treatment, time of heating, baking agents, fermentation time, additives and enzymes were reported in several studies. Nevertheless, since 2011 food AA levels seem to stagnate or even increase in some years. Thus, the food industry did not show sufficient progress in reducing AA. Reducing sugars and amino acid free asparagine (Asn) are the main AA precursors. They can fluctuate in their content for instance in grain flour or potatoes shifting the focus of AA origin to the raw material. Thus, the production of raw material low in AA precursors seems important. However, lowering precursors of AA in the raw material necessitates suitable agronomic strategies to grow cereal species and cultivars low, especially in free Asn. Hence, the major goal of this thesis was to investigate the following questions concerning their impact on free Asn formation in cereals: 1. Which role does the management system plays, as organic vs. conventional farming systems highly differ in their cropping strategies? 2. What is the best nitrogen fertilization strategy when comparing organic vs. conventionally cropping systems? 3. Is there an impact of sulphur fertilization concerning sulphur amount and sulphur type? 4. Can expanding row distance and lowering seed density in low-input farming systems positively influence baking quality while keeping free Asn amounts low? 5. For organically grown cereals no level of free Asn was available. Thus, the question came up to which extent organically grown cereal species and cultivars including ancient grains like einkorn and emmer differ in free Asn. 6. Should free Asn be implemented in breeding programs if heritability is high? 7. Is there an impact of harvest timing on free Asn formation? Out of several field trials the following results were obtained: • The cropping system had a significant impact on grain yield, the level of free Asn and quality traits. Across all species, free Asn contents in flour were 26% lower under organic conditions compared to conventional farming. For wheat a maximum reduction of 50% in free Asn content was possible if organically produced. Spelt and rye were affected to a minor extend as only in single years organically grown cultivars showed up to 33% lower Asn contents. • Nitrogen (N) fertilization significantly influenced grain yield and baking quality in both cropping systems. In contrast, up to a certain amount of N free Asn was only affected to a minor extend. In particular, within the organic farming samples no significantly higher free Asn amounts were determined even if N fertilizer was raised or the N form was changed. A late N fertilization within the conventional cropping system increased crude protein content, while no clear effect was found on free Asn. Also, cultivars affected free Asn level significantly. Wheat cultivar Capo exhibited the lowest AA formation potential at a N supply of 180 kg N ha−1 while simultaneously reaching a crude protein content > 15% (conventional) and > 12% (organic). Thus, lowering free Asn by adjusting N treatments should not necessarily affect baking quality. In general, free Asn amounts in wheat varied widely both within cultivars and between cropping systems. Besides N, neither type nor amount of sulphur fertilization influenced free Asn significantly. • Extending row distance can increase quality traits protein and sedimentation value. Seed density was highly related to grain yield and test weight. Most importantly, free Asn was only minor affected by both treatments. Thus, larger row distances can be recommended to raise baking quality in organic farming systems without simultaneously affecting free Asn. Number of grains spike-1 seems to be related to free Asn (R2=0.72). This provides new insights on Asn synthesis during grain development and offers the opportunity to predict free Asn formation without expensive chemical analyzes. In contrast Asn and protein content did not show any relation while high protein contents in grain seem to lower AA amount in heated flour samples. • The impact of organically grown cereal species and cultivars in combination with marginal N supply on free Asn was clearly shown. A reduction potential of 85% was reached if rye was replaced by spelt. Surprisingly, the ancient species einkorn and emmer reached a very high free Asn content similar to rye. Heritability was high for wheat and spelt concerning locations, while regarding years, heritability was low for wheat but high for spelt and rye. For organically grown cereals, the relation between free Asn and AA formation was proven. Across species and years free Asn can serve as an indicator for AA formation (R2 of 0.69). • Harvest timing affects free Asn levels. In this context a delayed harvest can increase Asn significantly while shifting harvest 1-2 weeks earlier decreased Asn by up to 60% depending on cereal species and cropping system. After summarizing and stating the most promising steps in the frame of agronomic strategies to lower free Asn, a prediction tool for free Asn should be implemented that classifies the impact of agronomic strategies and leads to recommendations to farmers. Finally, the main riddle, that should be solved during the next studies is the question, why cereal species and cultivars differ in their Asn formation. This thesis gives some preliminary ideas but a much deeper insight is essential to establish long-term strategies to lower free Asn content.
Alternative phosphorus resources from urban waste as fertilization
(2023) You, Yawen; Müller, Torsten
Phosphorus (P) is an essential macronutrient for plants. Plant roots assimilate P in soil mainly in the form of orthophosphates as H2PO4- and HPO42-. Due to the high reactivity, orthophosphates generally exist at low concentrations in soils that have high P sorption capacity. Besides the indigenous P in soil, fertilizers manufactured from phosphate rock are the main source of P to ensure a satisfactory yield in agricultural production. However, phosphate rock is a limited reserve with uneven quality and is geographically restricted. Technologies for recovering and reusing the P from waste streams were therefore developed to alleviate the dependency on this critical raw material and to promote sustainable solutions. Sewage sludge, which contains most of the P from wastewater, has great potential to produce P-rich products. However, the evaluation of their P availabilities to plants by simple chemical extraction of the product is difficult because they often contain different P species that do not easily dissolve in water. In the first chapter, three types of recycled P fertilizers derived from sewage sludge were tested first in the greenhouse using maize in two different substrates and were incubated in soil for 0, 22, and 56 days. Untreated sewage sludge ash (SSA), Na-treated SSA, and struvite were tested here. Untreated SSA failed to promote the growth of young maize, while Na-treated SSA and struvite achieved similar biomass as mineral P fertilizer. The pre-incubation time had a negative impact on the P use efficiency of recycled fertilizers. Although the P availability of untreated SSA was very low, it might be a potential substitute for phosphate rock to produce fertilizers. In Chapter II, the P availability and heavy metal contamination risk of superphosphate produced with untreated SSA in the lab were investigated. It was found that the superphosphate produced with the mixture of 25% SSA and 75% rock phosphate had a similar P use efficiency as the superphosphate produced with 100% rock phosphate, indicating untreated SSA could be a suitable substitution of rock phosphate in the P fertilizer production. Despite the heavy metal accumulations in soil and plant being minimal, the Pb and Cu concentration in untreated SSA exceeded the maximum limit according to the EU regulation on fertilizers and therefore its use is restricted in fertilizer production. The separation of industrial and municipal sludge before incineration is recommended to obtain SSAs with high P concentrations but less heavy metal. In Chapter III, the P availability of granulated struvite as affected by fertilizer application methods in comparison to di-ammonium phosphate (DAP) was investigated under field conditions. The experiment was conducted in one field in 2020 and repeated in an adjacent field in 2021. Two-year maize results showed an increase of 30% in maize yield and P content when struvite was placed, indicating that fertilizer placement enhanced the efficiency of granulated struvite. Struvite-placed had similar P use efficiency as DAP-placed, and both treatments led to significantly higher yield and P content of maize than no-P control. The residual effect of fertilizer treatment was evaluated with faba bean (Vicia faba) and triticale (Triticosecale Wittm. ex A. Camus.) as subsequent crops after maize. No significant difference in yield and P content was found between struvite-placed and DAP-placed. Nevertheless, this chapter demonstrated that placed struvite can replace DAP as P fertilizer in maize cultivation. In Chapter IV, the sensitivity of three P extraction methods to different P species was investigated to provide insights into the characterization of current soil P tests to plant P availability. Three soil P tests were compared: calcium acetate-lactate (CAL), Olsen, and diffusive gradients in thin films (DGT). Results showed that a portion of added orthophosphates was immediately fixed in the soil and cannot be extracted by any of the methods. The acidic CAL method may overestimate immediately plant-available P of insoluble calcium phosphate like Ca3(PO4)2. The most suitable method to determine immediately available P might be the Olsen and DGT method. To conclude, this dissertation demonstrated the P availability of recycled P fertilizers derived from sewage sludge and possible strategies to enhance their P use efficiencies. It provided agronomic evidence on the feasibility of replacing phosphate rock-derived P fertilizers with recycled fertilizers and insight into its land application. With the recently revised EU regulation on fertilizing products, it can be expected that recycled fertilizers will soon share the market with mineral fertilizers and help develop sustainable agriculture.
Ammonium fertilization increases the susceptibility to fungal leaf and root pathogens in winter wheat
(2022) Maywald, Niels Julian; Mang, Melissa; Pahls, Nathalie; Neumann, Günter; Ludewig, Uwe; Francioli, Davide
Nitrogen (N) fertilization is indispensable for high yields in agriculture due to its central role in plant growth and fitness. Different N forms affect plant defense against foliar pathogens and may alter soil–plant-microbe interactions. To date, however, the complex relationships between N forms and host defense are poorly understood. For this purpose, nitrate, ammonium, and cyanamide were compared in greenhouse pot trials with the aim to suppress two important fungal wheat pathogens Blumeria graminis f. sp. tritici (Bgt) and Gaeumannomyces graminis f. sp. tritici (Ggt). Wheat inoculated with the foliar pathogen Bgt was comparatively up to 80% less infested when fertilized with nitrate or cyanamide than with ammonium. Likewise, soil inoculation with the fungal pathogen Ggt revealed a 38% higher percentage of take-all infected roots in ammonium-fertilized plants. The bacterial rhizosphere microbiome was little affected by the N form, whereas the fungal community composition and structure were shaped by the different N fertilization, as revealed from metabarcoding data. Importantly, we observed a higher abundance of fungal pathogenic taxa in the ammonium-fertilized treatment compared to the other N treatments. Taken together, our findings demonstrated the critical role of fertilized N forms for host–pathogen interactions and wheat rhizosphere microbiome assemblage, which are relevant for plant fitness and performance.
Analyse von Wachstum und Qualität von Weizen unter ansteigender CO2 Konzentration als Folge des Klimawandels
(2019) Dier, Markus; Zörb, Christian
The atmospheric CO2 concentration is expected to increase to 500–620 ppm in the future. Such an elevated atmospheric CO2 concentration (e[CO2]) increases grain yield, but can decrease tissue N concentrations by about 9% in wheat. This could endanger global food security. Moreover, in previous studies, a decrease of grain N concentration by e[CO2] has closely been associated with that of gluten proteins, indicating a decreased baking quality under e[CO2]. The mechanisms by which e[CO2] decreases N concentration are still unclear and FACE studies investigating CO2 x N interactions on the formation of grain yield and the quality of winter wheat are scarce. The first main objective was the analysis of a decreased N concentration in the grain by e[CO2] in winter wheat based on a two-year FACE experiment with widely differing N levels (35 to 320 kg N ha-1) and different N forms (NO3- and NH4+). The focus was on key processes of grain N acquisition that are leaf NO3- assimilation, N remobilization and post-anthesis N uptake. The hypotheses were: e[CO2] inhibits leaf NO3- assimilation, e[CO2] decreases N remobilization (Nrem) by decreased N concentrations at anthesis and e[CO2] decreases post-anthesis N uptake (Nabs) by inhibition of leaf NO3- assimilation or acceleration of senescence. The second main objective was the simultaneous analysis of the e[CO2] effect on the grain proteome and baking quality with the hypothesis that e[CO2] reduces gluten proteins and thereby baking quality. e[CO2] increased grain yield in all N levels by 10% to 17% mainly through enhanced grain number per m2 ground area. This was due to increased radiation use efficiency (chapter 2). These increases were smaller under N deficiency compared with high N supply. The reasons were a reduction of photosynthesis capacity by e[CO2] and a sink limitation concerning grain yield due to N deficiency during ear growth. The indication for the reduction of photosynthesis capacity was a decrease of leaf N concentration under e[CO2] regardless of green leaf area index under N deficiency. An indication for sink limitation of grain yield was the decrease of harvest index by e[CO2] because of a strong and small stimulation of stem and ear growth, respectively by e[CO2]. Grain N yield was increased by e[CO2] under all N levels (chapter 3). There was a strong linear relation between grain N yield and grain number that was unaffected by e[CO2]. In contrast with the hypotheses of an decreased Nrem and Nabs under e[CO2], e[CO2] resulted in an increase of Nrem, Nrem efficiency and Nabs, causing the increase of grain N yield. Nevertheless, e[CO2] slightly decreased grain N concentration (by 1 to 6%), whereby the smallest effect of 1% was found under N deficiency. This decrease was primarily related to a growth dilution effect due to an increased individual grain weight under e[CO2]. A further reason was a stronger increase of grain number than an increase of vegetative N yield at anthesis by e[CO2] and thereby a decrease of the ratio between the N source and the N sink. Indication for an e[CO2] induced inhibition of leaf NO3- assimilation was not found as e[CO2] did not result in a decreased activity of leaf nitrate reductase under all N levels at both cool (17 °C) and warm (28 °C) temperatures (chapter 4). Furthermore, the e[CO2] induced stimulation of growth and N acquisition was not stronger under NH4+ compared with NO3- based N-fertilization. Reduction of grain protein concentration by e[CO2] was associated with reduced albumin/globulin and gluten concentrations under all N levels (chapter 5). Under optimal N supply, the grain protein composition was changed by e[CO2] with altogether 19 decreased and 17 increased protein spots. 15 out of the 16 identified decreased proteins were globulins, whereas specific gluten proteins were not found to be affected by e[CO2]. Correspondingly, baking quality remained unaffected under e[CO2] under all N conditions. In conclusion, grain N yields were increased by e[CO2] due to an increase of Nrem and Nabs with grain number being the driving force. Grain N concentrations were slightly reduced under e[CO2] with a growth dilution effect and a changed source to sink ratio as the underlying mechanisms. The reduction of the grain N concentration by e[CO2] was not specifically associated with a reduction of gluten proteins.
Analysis of phytotoxicity and plant growth stimulation by multi-walled carbon nanotubes
(2016) Zaytseva, Olga; Neumann, Günter
Nanotechnology is a rapidly expanding area of science and technology, which has gained a great interest due extraordinary properties of nanomaterials with numerous potential fields for practical application. Meanwhile, carbon nanotubes (CNTs) are among the ten most-produced engineered nanomaterials worldwide with applications in automotive industry, building and construction, electronics, and many other industrial sectors, showing also a great potential for integration into environmental and agricultural applications. However, during the last decade it has been demonstrated that nanomaterials can exert significant and extremely variable effects also on living organisms. In higher plants, both, positive and negative responses on growth and development have been reported but the related mechanisms are still not entirely understood. This study presents a systematic assessment of CNT effects on representative crops under standardized conditions with special emphasis on interactions with plant nutrition. After the introductory background (Chapter 1), presenting a comprehensive literature review on carbon nanomaterials with special emphasis on plant responses, environmental and agricultural applications, Chapter 2 describes the impact of selected multi-walled carbon nanotubes (MWCNTs) on seed germination and early seedling development of different crops (soybean−Glycine max, maize−Zea mays, and common bean−Phaseolus vulgaris). In face of highly variable plant responses to CNT treatments reported in the literature, the study was designed as a systematic analysis under standardized growth conditions, dissecting the effects of one single type of MWCNTs, depending on plant species, MWCNT dosage, duration of exposure to MWCNT treatments, and plant-developmental stage, including imbibition, germination and seedling development. Short-term seed treatments (36 h) with MWCNTs reduced the speed of water uptake particularly by soybean seeds, associated with an increased germination percentage and reduced formation of abnormal seedlings. However, during later seedling development, negative effects on fine root production were recorded for all investigated plant species. Inhibition of root growth was associated with reduced metabolic activity of the root tissue and a reduction of nitrate uptake, which could be mainly attributed to the smaller root system. The results demonstrated that even under standardized growth conditions largely excluding external factors, plant responses to MWCNT exposure exhibit differences, depending on plant species but also on the physiological status and the developmental stage of individual plants. Soybean was selected as a model plant for further studies since both, positive and negative effects of the same dose of MWCNTs (1000 mg L-1) could be observed even in the same individual plants. Chapter 3 investigates effects of short-term soybean seed exposure (36 h) to MWCNTs on seedling development, depending on the nutrient availability of the substrate. At 8 DAS stunted growth and poor fine root production were first detectable in seedlings germinating on moist filter paper without additional nutrient supply. This effect was preceded by reduced metabolic activity of the seedling tissues detectable by vital staining already at 2 DAS. Root growth inhibition was a long-lasting effect, detectable in soil culture up to 38 DAS. More detailed investigations revealed zinc (Zn) deficiency as a major growth-limiting factor. The growth of affected soil-grown plants was recovered by foliar application of ZnSO4 or by cultivation in nutrient solution supplied with soluble ZnSO4. A more detailed investigation of the physiological mechanisms related with the inhibitory effects of MWCNTs on plant growth is presented in Chapter 4. Oxidative stress was identified as a major factor determining MWCNT-induced root growth inhibition in soybean, demonstrated by recovery of root development after external supplementation with antioxidants. Induction of oxidative stress by MWCNT application was detectable already after the 36 h imbibition period particularly in the tips of the radicle as indicated by accumulation of superoxide anions, reduced triphenyltetrazolium chloride vital staining, and induction of superoxide dismutase activity. The expression pattern of the oxidative stress indicators coincided with preferential accumulation of MWCNTs in the cells of the root tip and was reverted by external application of proline as antioxidant. MWCNT-induced plant damage could be reverted by external supplementation of micronutrients (Zn, Cu, Mn) as important cofactors for various enzymes involved in oxidative stress defense (SOD, biosynthesis of antioxidative phenolics). Accordingly, SOD activity increased in seedling roots after Zn supplementation. During germination, the CNT treatments inhibited particularly the Zn translocation from the cotyledons to the growing seedling, and CNTs exhibited a selective adsorption potential for Zn and Cu, which may be involved in internal immobilization of micronutrients. Therefore, this study demonstrated for the first time that phytotoxicity of CNTs is linked with disturbances of micronutrient homeostasis during seedling development. Implications for environmental phytotoxicity assessment of MWCNTs and their potential applications in agriculture are discussed in a final overview presented in Chapter 5.
Analysis of the interaction between the helper component proteinase (HC-Pro) of Zucchini yellow mosaic virus (ZYMV) and the plant RNA methyltransferase Hua enhancer 1 (HEN1)
(2012) Jamoos, Rana; Reustle, Götz
The helper component-proteinase (HC-Pro) is a multifunctional protein found among potyviruses. It plays multiple roles in the viral infection cycle and some of these functions have been mapped to different regions of the protein. The subcellular localization of several viral RNA silencing suppressor (RSS) proteins was identified. In this study, we have shown that the Zucchini yellow mosaic virus (ZYMV) HC-Pro wild type (HC-ProFRNK) and its mutant, HC-ProFINK, had a diffuse cytoplasmic localization and formed aggregates along the endoplasmatic reticulum (ER). HC-ProFRNK and HC-ProFINK were stably expressed in N. benthamiana and A. thaliana plants. In addition, the HC-ProFRNK and HC-ProFINK were fused to a nuclear localization signal (NLS) sequence (NLS-HC-ProFRNK and NLS-HC-ProFINK) and these transgenes constructs were also stably transformed into N. benthamiana and A. thaliana. Expression of all four transgenes caused different effects in the two plant species. HC-ProFRNK?producing A. thaliana plants displayed severe phenotypic alterations. In A. thaliana, the HC-ProFINK led to a reduced number of seed set. In N. benthamiana expressing HC-ProFRNK/FINK, generally no or only slight phenotypic changes were monitored. The NLS-HC-ProFRNK/FINK-producing plants displayed clear phenotypes. Flower malformations and severe reduction of seed set were the most conspicuous observations made. In general, more severe developmental disturbances were observed in transgenic A. thaliana than in N. benthamiana plants. ZYMV HC-Pro RSS activity was previously demonstrated in N. benthamiana plants by transient expression experiments. In this study, RSS activity was confirmed in N. benthamiana lines stably expressing ZYMV HC-ProFRNK/FINK. Notably, these plants did not show significant morphological alterations. Because the RSS activity of HC-Pro leads to enhanced transgene expression, our ?symptom-free? transgenic N. benthamiana plants may serve as a platform for over-expression of foreign genes. In tobacco, transient or over-expression of rgs-CaM mimicked the phenotypic effects of Tobacco etch virus (TEV) HC-Pro, indicating that TEV HC-Pro may up-regulate rgs-CaM expression. However, our data revealed no significant difference in the levels of rgs?CaM mRNA in N. benthamiana plants expressing HC-ProFRNK/FINK when compared with the steady-state mRNA level found in the wild type plants. It is likely that RSS proteins from related viruses do not necessarily exhibit identical effects on RNA silencing. In addition, plant species might also differentially respond to identical RSS proteins. The small RNA (sRNA) binding activity of HC-Pro was evident in N. benthamiana plants co-expressing the HC-ProFRNK and an infectious transgene construct of Potato spindle tuber viroid (PSTVd). In comparison to PSTVd-infected N. benthamiana plants, Northern blot analysis showed increase accumulation of viroid-derived sRNAs in the double transformed plants. There is indirect evidence showing that in plants, transient or stable expression of HC-Pro results in decreased accumulation of methylated sRNAs. In this study, we demonstrated that recombinant ZYMV HC-Pro inhibited the methyltransferase activity of the A. thaliana Hua enhancer 1 (AtHEN1) in vitro. Moreover, we found that HC-ProFINK lacking sRNA-binding activity, also inhibited AtHEN1 activity. In contrast, truncated HC-Pro and total soluble bacterial proteins did not affect AtHEN1 activity. Using enzyme-linked immunosorbent assays, we provided evidence that the HC-ProFRNK/FINK, both bound to AtHEN1. Our results strongly indicated that inhibition of the AtHEN1 activity by HC-Pro is probably due to direct interactions between both proteins. We concluded that AtHEN1 inhibition and sRNA-binding activities of HC-Pro are independent of each other. Using the yeast two-hybrid (Y2H) system, we could show that in contrast to RSS proteins from some other viruses, the HC-ProFRNK/FINK proteins did not interact with the Argonaute 1 (AGO1) protein. Similar to previous reports our data confirmed that HC-Pro interacts with itself to form homodimers. Notably, only HC-ProFRNK but not HC-ProFINK was able to interact with itself. The conserved FRNK box is located in the central domain of HC-Pro and this domain has been previously shown to be involved in self-interaction. It should be noted that parts of the work have been published in: - Jamous R. M., Boonrod K., Fuellgrabe M. W., Ali-Shtayeh M. S., Krczal G. and Wassenegger M. (2011). The HC-Pro of the Zucchini Yellow Mosaic Virus (ZYMV) inhibits HEN1 methytransferase activity in vitro. J. Gen. Virol. 92, 2222-2226. - Fuellgrabe M., Boonrod K., Jamous R., Moser M., Shiboleth Y., Krczal G. and Wassenegger M. (2011). Expression, purification and functional characterization of recombinant Zucchini yellow mosaic virus HC-Pro. Protein Expr. Purif. 75: 40-45.
Application of infrared imaging for early detection of downy mildew (Plasmopara viticola) in grapevine
(2022) Zia-Khan, Shamaila; Kleb, Melissa; Merkt, Nikolaus; Schock, Steffen; Müller, Joachim
Late detection of fungal infection is the main cause of inadequate disease control, affecting fruit quality and reducing yield of grapevine. Therefore, infrared imagery as a remote sensing technique was investigated in this study as a potential tool for early disease detection. Experiments were conducted under field conditions, and the effects of temporal and spatial variability in the leaf temperature of grapevine infected by Plasmopara viticola were studied. Evidence of the grapevine’s thermal response is a 3.2 °C increase in leaf temperature that occurred long before visible symptoms appeared. In our study, a correlation of R2 = 0.76 at high significance level (p ≤ 0.001) was found between disease severity and MTD. Since the pathogen attack alters plant metabolic activities and stomatal conductance, the sensitivity of leaf temperature to leaf transpiration is high and can be used to monitor irregularities in temperature at an early stage of pathogen development.
Approaches to improve the implementation and expansion of Miscanthus production
(2016) Xue, Shuai; Lewandowski, Iris
Several species within the miscanthus genus (Miscanthus spp.) are characterized by high biomass yields and low production input requirements. This raised increasing interests in their applications for bioenergy. However, to date, only small areas of Miscanthus × giganteus (approximately 40,000 ha) are commercially grown and used for generating electricity and heat in Europe, where miscanthus has been developed as bioenergy crop for more than decade. Reviewing state-of-the-art revealed four main factors limiting the implementation of miscanthus production. These are inefficient and expensive propagation techniques, land use dilemma (i.e. lack of land available for growing miscanthus), lack of varieties/genotypes adapted to various and especially to stressful environmental conditions and lack of efficient agronomic practices for miscanthus establishment. Against these limiting factors, this thesis aims to (1) evaluate the different propagation systems with regard to technologies and costs, and improve the preferred rhizome propagation techniques; (2) address the land use dilemma through exploring marginal land (i.e. non-arable land with ability to grow plants with tolerance to environmental stresses) for miscathus production; (3) and screen optimal genotypes and effective practices for establishing and managing miscanthus on marginal land in a case study on grassland. To achieve the first objective, a review, our own field trials and farmer surveys were performed. Direct seed sowing was found to be the cheapest propagation method (1,508.5 € ha-1 overall establishment costs) and micro-propagation the most expensive (6,320.8 € ha-1). Direct rhizome planting is the farmers’ most preferred and most applied establishment method and has moderate establishment cost of 1,904-3,375.7 € ha-1. However, it goes along with the lowest propagation efficiency (1:10) and consequently restricts the availability of propagation material for large-scale plantations. However, the multiplication ratio can be increased by reducing the rhizome size. Field trial results showed that 6-cm length is close to the minimum size of rhizome that can germinate after directly planting into field. Compared to the traditionally used macro-rhizome, the multiplication ratio of the improved rhizome propagation (using 6-cm rhizomes) is tripled. In addition, the multiplication ratio can also be increased by transplanting rhizome- or stem-derived plantlets. However, due to higher labour and energy inputs required for the pre-growing of plantlets, their establishment cost reduction potential is limited, with estimated costs of 4,240.8-4,400.8 € ha-1. Direct seed sowing as the cheapest method is presently only possible for Miscanthus sinensis and not yet practical under German conditions. In addition, the seed-setting rate of M. sinensis is very low (0.0-28.7%) under the climatic conditions of south-west Germany, making commercial seeds production difficult. For all the propagation methods considered, more research efforts are still required to reduce the material production costs and simultaneously increase the multiplication ratio. For the second objective, the production potential of miscanthus on marginal land in China was assessed. Because China has limited agricultural land resources and its non-food bioenergy policy (it is only allowed to grow energy crops on marginal land) is adamant, there is a desideration for exploiting its marginal land potential. In this study, Geographic Information System (GIS) techniques, model simulation were adopted to identify the productive marginal areas for miscanthus and to estimate their biomass and bioenergy production potentials. The results show that in China there are large marginal land areas of 17,163.54 × 104 ha available for growing miscanthus. However, due to limitation by low winter temperatures and low precipitation levels in some areas, the total marginal area suitable for growing miscanthus is only 769.37 × 104 ha. The Monteith radiation yield model was used to determine the potential miscanthus yield in Chinese climatic conditions. The simulation gave the actual harvestable yield levels on arable land of 18.1-44.2 odt ha-1 yr-1. Taking the environmental stresses of marginal conditions into account an achievable miscanthus yield potential on marginal land of 2.1-32.4 odt ha-1 yr-1 was calculated (varying between different marginal land types). Based on these achievable yield levels, the total miscanthus production potential on the entire suitable marginal land areas is 13,521.7 × 104 odt yr-1; the corresponding bio-electricity generation and total greenhouse gas saving potentials are 183.9 TW h yr-1 and 21,242.4 × 104 t CO2 eq. yr-1, respectively. The spatial distribution of the suitable marginal areas shows that they are mainly concentrated in the central part of Northeast China and the Loess Plateau. Both regions are recommended as priority development zones for the Chinese miscanthus-based bioenergy industry. However, implementation of this huge marginal land potential is currently constrained by many barriers, e.g. concerns on potential ecological effects, competition for marginal land from other uses, lack of high yield varieties in marginal conditions. Lack of varieties with suitability to marginal conditions and efficient agronomic practices for the establishment on marginal land are the main barriers that limit using marginal land for miscanthus production. Therefore, stress tolerant varieties need to be selected and methods of effective establishment of miscanthus on marginal land need to be developed. Worldwide, grassland is the most important marginal land type because it has the largest terrestrial area and mild environmental stresses for growing energy crops (including miscanthus). However, it is undesirable or even legally prohibited to convert grassland into bioenergy cropland to avoid biodiversity loss and soil carbon being reduced by tilling practices. Hence, no-till establishment practices for miscanthus establishment and maintenance on grassland are investigated here under the third objectives. Our study demonstrates that miscanthus can be successfully cultivated on both good (nutrient-rich) and marginal (nutrient-poor) grassland using the proposed agronomic practices and an increased grassland productivity may be achieved through the establishment of suitable miscanthus genotypes. The recommended agronomic practices are summarized as following. Miscanthus genotypes with tall, thick shoots perform better than those with short, thin shoots. Better establishment is achieved when rhizome-derived plantlets are transplanted into pre-disturbed grassland. The grassland pre-disturbance of low vegetation cutting (5 cm) and herbicide spraying in narrow stripes is recommended for its beneficial effect on miscanthus establishment without significant negative effects on grassland productivity. Two harvests, one in late spring and one in late autumn, are optimal to achieve a high grassland yield. In this thesis, the limitation of the inefficient propagation technique was mitigated through minimizing the rhizome size and exploring the seeds propagation potential. The land-use dilemma was alleviated by exploring the marginal land production potential. Additionally, constrains of lack of genotypes and agronomic practices for the miscanthus establishment on marginal land were improved by field trials on grassland (the most important marginal land type with a huge potential).These results can improve the implementation and expansion of miscanthus production. However, in addition to constrains improved in this thesis, the miscanthus production is currently constrained by many other technical, economic and financial, social and political, environmental issues. It is unlikely that the implementation and expansion will achieve without mitigating these constrains. Further research and support should address these barriers in an integrate manner.
Aspects of stomatal physiology during salt-stress-related disturbances of ion homeostasis
(2020) Franzisky, Bastian Leander; Zörb, Christian
Soil salinity is a major challenge for agriculture, because most crop plants are sensitive to high salt concentrations in soil, an environment that results in reduced growth and yield. One major constraint imposed by salinity is the disruption of ion homeostasis attributable to the uptake competition of salts and nutrients and the accumulation of deleterious ions, which are toxic to plants at high concentrations. For a better understanding of ion-homeostasis-associated traits contributing to salt tolerance in salt-sensitive crops, such as Vicia faba and Zea mays, the capabilities of ion exclusion and tissue tolerance were assessed in diverse genotype selections under saline conditions. In addition, the impact of increased salt ion concentrations in leaves and in the apoplast on stomatal physiology and guard cell integrity was characterized in V. faba exposed to long term salinity in order to improve our knowledge of stomatal physiology and functioning under conditions of NaCl stress. The treatment of diverse V. faba varieties with 100 mM NaCl demonstrated that ion homeostasis-associated tolerance mechanisms are differentially managed for Na+ and Cl-. The longer-withstanding varieties were tolerant to the accumulation of Na+ suggesting that tolerance to Na+ predominantly occurred at the level of tissue tolerance after Na+ had entered the leaves. Conversely, tissue tolerance for Cl- was weak throughout all varieties suggesting that the tolerance to Cl- was facilitated instead by the restriction of the intrusion of Cl- into the plant’s shoots; this process might be crucial for the ability of V. faba to withstand NaCl salinity. The treatment of diverse Z. mays hybrids with mild and high doses of Cl- added to the soil revealed that most genotypes restricted Cl- root to shoot translocation. This suggests that Z. mays effectively prevents Cl- from entering the xylem and, thus, the acropetal transport of Cl-, thereby hindering harmful Cl- accumulations building up in the photosynthetically active leaf blades. A detailed analysis of guard cell physiology under long-term NaCl demonstrated that guard cell primary metabolism differentially responds to altered ion composition resulting from salt stress in comparison with whole leaf tissue in V. faba; such a differential response might be a prerequisite for the maintenance of guard cell functionality under conditions of stress, i.e. the adjustment of guard cell turgor that affects stomatal aperture and water loss. Moreover, the shift from a photoperiod dependent accumulation of sucrose in guard cells and the apoplast to a photoperiod independent under salinity suggests that a metabolic sucrose-mediated feedforward mechanism is involved in coordinating stomatal closure under conditions of long term NaCl and might be beneficial for reducing water loss under conditions of stress related carbon partitioning. In summary, this work shows that ion-homeostasis associated tolerance traits vary between crop species and that the differential metabolic acclimatisation of guard cells to disturbed ion homeostasis might represent an important aspect of tissue tolerance enabling the maintenance of stomatal regulation during long term salinity.
Assessing long term effects of compost fertilization on soil fertility and nitrogen mineralization rate
(2023) Reimer, Marie; Kopp, Clara; Hartmann, Tobias; Zimmermann, Heidi; Ruser, Reiner; Schulz, Rudolf; Müller, Torsten; Möller, Kurt
Fertilization with organic waste compost can close the nutrient cycles between urban and rural environments. However, its effect on yield and soil fertility must be investigated. This study investigated the long-term effect of compost on soil nutrient and potentially toxic elements (PTEs) concentration, nutrient budgets, and nitrogen (N) mineralization and efficiency. After 21 years of annual compost application (100/400 kg N ha–1 year–1 [100BC/400BC]) alone and combined with mineral fertilization, soil was analyzed for pH, organic carbon (SOC), nutrient (total N and P, Nmin, extractable CAL-P, CAL-K, and Mg), and PTE (Cu, Ni, Zn) concentrations. Yields were recorded and nutrient/PTE budgets and apparent net mineralization (ANM, only 2019) were calculated. N efficiency was the highest in maize and for mineral fertilization. Compost application led to lower N efficiencies, but increased ANM, SOC, pH, and soil N, and surpluses of N, P, and all PTEs. Higher PTE concentrations were only found in 400BC for Cu. Nutrient budgets correlated with soil nutrient concentration. A surplus of 16.1 kg P ha–1 year–1 and 19.5 kg K ha–1 year–1 resulted in 1 mg kg–1 increase in CAL-P and CAL-K over 21 years. Compost application supplies nutrients to crops with a minor risk of soil-accumulation of PTEs. However, the nutrient stoichiometry provided by compost does not match crop offtakes causing imbalances. Synchronization of compost N mineralization and plant N demand does not match and limits the yield effect. In winter wheat only 65–70% of N mineralization occurred during the growth period.
Assessment of a postharvest treatment with pyrimethanil via thermo-nebulization in controlling storage rots of apples
(2021) Büchele, Felix; Neuwald, Daniel A.; Scheer, Christian; Wood, Rachael M.; Vögele, Ralf T.; Wünsche, Jens N.
Apples are very susceptible to infections from various fungal pathogens during the growing season due to prolonged exposure to environmental influences in the field. Therefore, a strict and targeted fungicide strategy is essential to protect fruit and trees. Increased environmental and health concerns and pathogen resistance have resulted in a rising demand to reduce fungicide usage and residues on marketed fruit. Thus, producers must develop new plant protection strategies to conform to the legal and social demands while still offering high-quality apples. This study assessed the efficacy of a post-harvest fungicide treatment with pyrimethanil via thermo-nebulization for controlling storage rots and compared the results to those of standard pre-harvest fungicide strategies. The results showed that a single post-harvest application of pyrimethanil successfully controlled storage rots and is comparable to strategies using multiple pre-harvest fungicide applications. The control of fungal rot was sustained even after 5 months of storage and 2 weeks of shelf life. Thermo-nebulization into the storage facility allowed for a lower dosage of fungicide to be used compared to pre-harvest applications, while still maintaining optimal rot control. Residue analyses showed that the post-harvest fungicide treatment did not exceed legal or retailer’s standards.
Banana weevil borer (Cosmopolites sordidus) : plant defense responses and control options
(2021) Bakaze, Elyeza; Wünsche, Jens Norbert
Each year 25-75% of banana yields are lost to Cosmopolites sordidus, one of the major pests of banana/plantain plants. This loss is common with resource-limited farmers who cannot afford the frequent application of insecticides due to their cost and developed resistance by weevils. Larvae, the most destructive life stage, occupy ecologically different microenvironments from adult weevils, thus least affected by synthetic insecticides. Feeding of larvae on banana rhizomes interferes with the established and emerging roots which reduce water and nutrient uptake and consequently weaken the plant stability during windy weather. Integrated pest management (IPM) is being promoted, for a single control strategy produces limited and or unsustainable results. IPM options for banana weevils include habitat management (cultural control), biological control, host resistance, botanical control and chemical control as last resort. Of the above IPM strategies, this research evaluated host resistance, botanical plant extracts and entomogenous fungi to contribute to the overall goal of reducing synthetic insecticides use. In the evaluation of host resistance, physiochemical of phenolic origin; lignin, and suberin were considered. Comparably, weevil and methyl jasmonate treatment, induced higher deposits of lignin and suberin, cellular modifications, and high total phenolic content as well as antioxidant capacity in “Km5” than “Mbwazirume” banana cultivars. Induced polyphenols reduced weevil damage to less than 5% in “Km5” compared to 11% damage in the “Mbwazirume” cultivar. However, with the onetime application of 0.01% methyl jasmonate, “Mbwazirume”, had 50% reduced weevil damage compared to untreated control. Extracts from dried clove buds (Syzygium aromaticum), pepper fruits (Piper guineense) and neem seeds (Azadirachta indica) and their synthetic analogs were evaluated as botanical control option to Carbofuran against C. sordidus in the laboratory and infested field experiments. Efficacy of plant extracts and their synthetic analogs, revealed egg hatch inhibitory effect, larvicidal toxicity and adult repellency variation. For instance, clove extracts and its synthetic analogs had the lower egg inhibitory dose (ID50) of 0.08 to 0.22% than black pepper (0.24 to 0.75%), and half the ID50 value caused 50% larvae mortality. However, in 6 to 48 hours pepper repelled 80 - 98%, clove 78 - 90% and neem 63 - 75% adult weevils, an effect that significantly (P =0.001) reduced field weevil population. Lastly, three Entomogenous fungi; Curvularia senegalensis, Fusarium verticillioides, and Fusarium oxysporum species complex (FOSC) were also evaluated for their ability to infect weevil eggs, larvae and adult weevils, and to reduce weevil damage in potted plants. C. senegalensis and F. verticillioides greatly affected egg hatching and larval survival, for instance, they caused 75 to 90% eggs hatch inhibition, unlike the 25 to 55% egg hatch inhibition for Beauveria bassiana and FOSC. Besides that, fungal treated plants 14 days before weevils, had significantly high SPAD value (P <0.0001), less than 20% rhizome damage and predictive weevil mortality R2 = 0.46. Rhizome damage was greatly reduced by C. senegalensis, followed by B. bassiana and F. verticillioides, and it is the first record to demonstrate that C. senegalensis and F. verticillioides are pathogenic to C. sordidus. In conclusion, an IPM that combines host resistance with locally available botanic extracts and effective entomogenous fungi may provide a sustainable intervention in the management of the weevil population and their damages to benefit both commercial and resource-limited farmers.
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.
Beneficial microbial consortium improves winter rye performance by modulating bacterial communities in the rhizosphere and enhancing plant nutrient acquisition
(2023) Behr, Jan Helge; Kampouris, Ioannis D.; Babin, Doreen; Sommermann, Loreen; Francioli, Davide; Kuhl-Nagel, Theresa; Chowdhury, Soumitra Paul; Geistlinger, Joerg; Smalla, Kornelia; Neumann, Günter; Grosch, Rita
The beneficial effect of microbial consortium application on plants is strongly affected by soil conditions, which are influenced by farming practices. The establishment of microbial inoculants in the rhizosphere is a prerequisite for successful plant-microorganism interactions. This study investigated whether a consortium of beneficial microorganisms establishes in the rhizosphere of a winter crop during the vegetation period, including the winter growing season. In addition, we aimed for a better understanding of its effect on plant performance under different farming practices. Winter rye plants grown in a long-time field trial under conventional or organic farming practices were inoculated after plant emergence in autumn with a microbial consortium containing Pseudomonas sp. (RU47), Bacillus atrophaeus (ABi03) and Trichoderma harzianum (OMG16). The density of the microbial inoculants in the rhizosphere and root-associated soil was quantified in autumn and the following spring. Furthermore, the influence of the consortium on plant performance and on the rhizosphere bacterial community assembly was investigated using a multidisciplinary approach. Selective plating showed a high colonization density of individual microorganisms of the consortium in the rhizosphere and root-associated soil of winter rye throughout its early growth cycle. 16S rRNA gene amplicon sequencing showed that the farming practice affected mainly the rhizosphere bacterial communities in autumn and spring. However, the microbial consortium inoculated altered also the bacterial community composition at each sampling time point, especially at the beginning of the new growing season in spring. Inoculation of winter rye with the microbial consortium significantly improved the plant nutrient status and performance especially under organic farming. In summary, the microbial consortium showed sufficient efficacy throughout vegetation dormancy when inoculated in autumn and contributed to better plant performance, indicating the potential of microbe-based solutions in organic farming where nutrient availability is limited.

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