Browsing by Subject "Cold stress"

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    Advancing soybean adaptation to Central European growth conditions with novel breeding tools
    (2020) Jähne, Felix; Würschum, Tobias
    According to the European Soy Monitor 2018 (European Soy Monitor, 2018), there is a wide discrepancy in the EU between market demands and general sustainability aims regarding soybean products. Europe needs to take action, if it wants to maintain its protein demands and at the same time requests a reduction in the destruction of globally important tropical and subtropical ecosystems. One step towards more sustainable soybean products lies in the increase of domestic production which has the potential to decrease soybean imports from areas of unsustainable cultivation. An augmented EU production of soybeans can be achieved for example by increasing the yield potential of soybeans in areas where successful cultivation already takes place or by expanding the cultivation area to more northern parts of Central Europe. Breeding for new, improved and adapted soybean cultivars that meet those terms, is a key activity towards that aim. This dissertation elucidates three different ways how the adaptation of soybeans to the climatic and photoperiodic conditions of Central Europe can be assisted and even accelerated: 1) By using off-season climate-controlled LED chambers to enable a speed breeding single seed descent approach. A 10 h light regime, rich in blue and deprived of far-red light emission is capable to significantly reduce and synchronise the generation time of soybeans. It was possible to shorten the life cycle for a panel of 8 soybean cultivars from different maturity groups to 77 days. This allows several generations of soybeans to be grown within one year. For the short day crops rice and amaranth on the other hand, different light quality parameters were favoured. In those crops mean flowering time was accelerated when far-red light was included in the light protocol. This underlines the importance of a crop-specific light regime in order to realise the full potential of LED-based speed breeding single seed descent. 2) By including experiments in climate-control chambers in combination with molecular tools (i.e. genomic prediction) to advance cold tolerance in soybeans. This quantitatively inherited key trait is necessary to adapt soybeans to colder regions and consequently extend growing areas of this crop to higher latitudes in Europe. In the biparental soybean population Merlin × Sigalia (103 recombinant inbred lines) three QTL for cold tolerance during pod onset were found on chromosomes 7, 11 and 13. The relatively small proportion of genotypic variance for this trait explained by these QTL underlines the quantitative nature of cold tolerance. Genomic prediction was shown to be a promising approach to select for cold stress tolerance. Scenarios with different test set sizes and prediction models were evaluated. In scenarios with smaller test set sizes prediction accuracies increased if known and confirmed QTL were included in the prediction model. 3) By incorporating citizen science into the breeding process. The citizen science project ‘1000 Gärten’ from 2016 approached this topic. Phenotypic data from soybean cultivars and breeding lines were collected by citizen scientists in 2492 gardens throughout Germany which generated a unique dataset. Among many other results this study was able to show that in 2016 and within the early maturity segment of soybeans the factor temperature influenced flowering and maturity to a higher degree than photoperiod although day length differed by over an hour between the north and the south of Germany during the time of flowering. It was shown that this admittedly challenging tool can realise a significant impact not only regarding the possibility of a highly multi-environmental screening of breeding material but also by connecting plant breeding, agriculture and potential future costumers in order to raise awareness and acceptance of a crop in larger parts of the society - a factor that may not be highlighted enough when a new crop is introduced to our agriculture. These approaches should not be seen as an alternative to classical plant breeding, but rather considered as valuable additional tools that can contribute to conventional breeding of soybeans, as well as other crops. If applied, the presented tools may assist plant breeding to pave Europe’s way towards a greener and more sustainable future that is urgently needed.
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    Micronutrients, silicon and biostimulants as cold stress protectants in maize
    (2020) Moradtalab, Narges; Streck, Thilo
    Mitigation of abiotic stress in crops is a feature attributed to various so-called biostimulants based on plant growth-promoting microorganisms (PGPMs) plant-, compost- and seaweed extracts, protein hydrolylates, chitosan derivatives etc. but also to mineral nutrients with protective functions, such as zinc (Zn), manganese (Mn), boron (B), calcium (Ca) and silicon (Si), recommended as stress protectants in commercial formulations. This study focussed on the effects of selected biostimulants on cold stress mitigation during early growth in maize, as a major stress factor for cultivation of tropical and subtropical crops in temperate climates. Chilling stress and micronutrient supplementation Chilling stress, induced by moderately low soil temperatures (8-14°C) in a controlled root cooling system, was associated with inhibition of shoot growth, oxidative leaf damage (chlorosis, necrosis accumulation of stress anthocyanins) and a massive decline in root length (Chapter 4 and 5). Due to inhibition of root growth, nutrient acquisition in general was impaired. However, nutrient deficiencies were recorded particularly for the micronutrients zinc (Zn) and manganese (Mn). The impaired Zn and Mn status was obviously related with the observed limitations in plant performance, which were reverted by exogenous Zn and Mn supplementation (0.5 mg plant-1), finally leading to restored nutrient acquisition and improved plant recovery after termination of the cold stress period. Zinc and manganese deficiency was mainly related with impaired uptake of the micronutrients, since the cold stress-induced deficiency symptoms persisted even in hydroponic culture when all nutrients were freely available. Beneficial effects of Zn/Mn supplementation were only detectable when the micronutrients were supplied prior to the onset of the stress period via seed soaking, seed dressing or fertigation, when uptake and internal translocation was still possible. A transcriptome analysis of the shoot tissue (Chapter 5) revealed 1400 differentially expressed transcripts (DETs) after 7-days exposure of maize seedlings to chilling stress of 12°C, mostly associated with down-regulation of selected functional categories (BINs), related with photosynthesis, synthesis of amino acids, lipids and cell wall precursors, transport of mineral nutrients (N, P, K,), metal handling and synthesis of growth hormones (auxins, gibberellic acid) but also of jasmonic (JA) and salicylic acids (SA) involved in stress adaptations. In accordance with the impaired micronutrient status and oxidative leaf damage in response to the cold stress treatments, downregulation was also recorded for transcripts related with oxidative stress defence (superoxide dismutases SOD, catalase, peroxidases POD, synthesis of phenylpropanoids and lignification), particularly dependent on the supply of micronutrients as co-factors. Upregulation was recorded for BINs related with degradation of lipids, of cell wall precursors, synthesis of waxes and certain flavonoids and of stress hormones, such as abscisic acid (ABA) and ethylene but degradation of growth-promoting cytokinins (CK). Accordingly, supplementation of Zn and Mn increased the accumulation of anthocyanins and antioxidants, the activities of superoxide dismutase and peroxidases, associated with reduced ROS accumulation (H2O2), mitigation of oxidative leaf damage and improved plant recovery at the end of the cold stress period (Chapter 5 and 6). Effects of seaweed extracts Cold-protective properties similar to Zn/Mn supplementation, associated with an improved Zn/Mn-nutritional status and reduced oxidative damage, were recorded also after fertigation with seaweed extracts prior to the onset of the stress treatments (Chapter 4). However, this effect was detectable only with seaweed extract formulations rich in Zn/Mn (Algavyt+Zn/Mn; Algafect; 6-70 mg kg DM-1) but not with a more highly purified formulation (Superfifty) without detectable micronutrient contents. This finding suggests that the cold-protective effect by soil application of seaweed extracts is based on an improved micronutrient supply and not to an elicitor effect, frequently reported in the literature for stress-protective functions after foliar application of seaweed extracts. Silicon fertilization Similar to seaweed extracts, also silicon (Si), applied by seed soaking or fertigation with silicic acid, mimicked the cold-protective effects of Zn/Mn supplementation in maize seedlings (Chapter 5). The Zn/Mn status of the Si-treated plants was improved although, in this case no additional micronutrient supply was involved. However, Si application significantly reduced leaching losses of Zn/and Mn by 50-70%, as a consequence of cold stress-induced membrane damage in germinating maize seeds and favoured the root to shoot translocation of Zn. This was associated with a restoration of gene expression, similar to the profiles recorded for unstressed control plants. However, the expression of genes related with synthesis and signal transduction of ABA, as central regulator of adaptive cold stress responses in plants, was even more strongly upregulated than in the cold-stressed controls. Accordingly, expression of cold stress adaptations involved in oxidative stress defence (SOD, peroxidases, phenolics, antioxidants) and the reduction of oxidative leaf damage and improved plant recovery were similar to the plants with Zn/Mn supplementation. Plant growth promoting microorganisms Cold-protective functions were recorded also for selected microbial inoculants (Chapter 6). However, out of five tested inoculant formulations, based on strains of Pseudomonas sp., DSMZ13134, Bacillus amyloliquefaciens FZB42, Bacillus atrophaeus ABI05, Penicillium sp. PK112 (BFOD) and a consortium of Trichoderma harzianum OMG16 and five Bacillus strains (Combi-A), a significant protective effect was detectable only for Penicillium sp. and particularly for CombiA. The CombiA consortium significantly increased root length and reduced oxidative leaf damage of cold-stressed plants, associated with increased SOD and POD activities and accumulation of phenolics and antioxidants. Root growth stimulation was related with increased IAA (indole acetic acid) tissue contents and increased expression of genes involved in IAA biosynthesis (ZmTSA) transport (ZmPIN1A) and perception (ZmAFR12). The tissue concentrations of ABA were not affected by the microbial inoculants, but the shoot concentrations of JA and SA increased, suggesting an effect by induced systemic resistance (ISR). Moreover, root concentrations of cytokinins (CKs) as ABA antagonists and expression of IPT genes involved in CK biosynthesis declined, leading to an increased ABA/cytokinin ratio and accordingly to increased expression of ABA responsive genes (ZmABF2). These findings suggest that CombiA mainly acted via improvement of root growth and nutrient acquisition by activation of the plant auxin metabolism and activation of cold protective metabolic responses by induction of ISR via JA/SA signalling and ABA-mediated responses, due to inhibition of CK biosynthesis. Synergistic interactions While the different cold-stress protectants investigated in this study induced similar protective plant responses, synergistic effects were obtained by combined applications (Chapter 6). The combination of CombiA inoculation with Zn/Mn supplementation further increased the plant micronutrient status and the cold-protective effects of CombiA. For all treatments, generally the expression of cold-protective effects was further improved by use of DMPP-stabilized ammonium fertilizers instead of nitrate fertilization. Ammonium fertilization promoted micronutrient acquisition via root-induced rhizosphere acidification, increased the ABA shoot concentrations with a moderate activation of metabolic cold stress responses and stimulated root colonization of Trichoderma harzianum OMG16 (CombiA). Field performance A comparative evaluation of the various cold protectants under field conditions with stabilized ammonium starter fertilization, revealed a severely reduced seedling emergence at six weeks after sowing (44%) due to extremely cold and wet soil conditions by the end of April in 2016, associated with a low Zn-nutritional status (32 mg kg-1 shoot DM). Significant improvements were recorded particularly for starter treatments including Zn/Mn seed dressing (emergence 56%) or seed priming with K2SiO4 (emergence 72%) and also by inoculation with the fungal PGPM strain Penicillium sp. BFOD (emergence 49%) associated with a doubling of the Zn tissue concentrations. Even after re-sowing, a significant yield increase for silo maize was recorded exclusively for the K2SiO4 treatment (Chapter 5). Taken together, the findings suggest that exploitation of synergistic interactions by combined starter applications of protective nutrients with selected biostimulants, could offer a cost-effective option for cold-stress prophylaxis in sensitive crops.
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    Peruvian amaranth (kiwicha) accumulates higher levels of the unsaturated linoleic acid
    (2023) Kanbar, Adnan; Beisel, Julia; Gutierrez, Meylin Terrel; Graeff-Hönninger, Simone; Nick, Peter
    Grain amaranth (Amaranthus spp.) is an emerging crop rich in proteins and other valuable nutrients. It was domesticated twice, in Mexico and Peru. Although global trade is dominated by Mexican species of amaranth, Peruvian amaranth (A. caudatus, kiwicha) has remained neglected, although it harbours valuable traits. In the current study, we investigate the accumulation of polyunsaturated fatty acids, comparing four genotypes of A. caudatus with K432, a commercial variety deriving from the Mexican species A. hypochondriacus under the temperate environment of Southwest Germany. We show that the A. caudatus genotypes flowered later (only in late autumn), such that they were taller as compared to the Mexican hybrid but yielded fewer grains. The oil of kiwicha showed a significantly higher content of unsaturated fatty acids, especially of linoleic acid and α-linolenic acid compared to early flowering genotype K432. To gain insight into the molecular mechanisms behind these differences, we sequenced the genomes of the A. hypochondriacus × hybridus variety K432 and the Peruvian kiwicha genotype 8300 and identified the homologues for genes involved in the ω3 fatty-acid pathway and concurrent oxylipin metabolism, as well as of key factors for jasmonate signalling and cold acclimation. We followed the expression of these transcripts over three stages of seed development in all five genotypes. We find that transcripts for Δ6 desaturases are elevated in kiwicha, whereas in the Mexican hybrid, the concurrent lipoxygenase is more active, which is followed by the activation of jasmonate biosynthesis and signalling. The early accumulation of transcripts involved in cold-stress signalling reports that the Mexican hybrid experiences cold stress already early in autumn, whereas the kiwicha genotypes do not display indications for cold stress, except for the very final phase, when there were already freezing temperatures. We interpret the higher content of unsaturated fatty acids in the context of the different climatic conditions shaping domestication (tropical conditions in the case of Mexican amaranth, sharp cold snaps in the case of kiwicha) and suggest that kiwicha oil has high potential as functional food which can be developed further by tailoring genetic backgrounds, agricultural practice, and processing.