Browsing by Subject "Drought stress"

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Drought stress during anthesis alters grain protein composition and improves bread quality in field-grown Iranian and German wheat genotypes
(2021) Rekowski, Azin; Wimmer, Monika A.; Tahmasebi, Sirous; Dier, Markus; Kalmbach, Sarah; Hitzmann, Bernd; Zörb, Christian
Drought stress is playing an increasingly important role in crop production due to climate change. To investigate the effects of drought stress on protein quantity and quality of wheat, two Iranian (Alvand, Mihan) and four German (Impression, Discus, Rumor, Hybery) winter wheat genotypes, representing different quality classes and grain protein levels, were grown under field conditions in Eqlid (Iran) during the 2018–2019 growing season. Drought stress was initiated by interrupting field irrigation during the anthesis phase at two different stress levels. Drought stress at anthesis did not significantly change total grain protein concentration in any of the wheat genotypes. Similarly, concentrations of grain storage protein sub-fractions of albumin/globulin, gliadin and glutenin were unaltered in five of the six genotypes. However, analysis of protein sub-fractions by SDS polyacrylamide gel electrophoresis revealed a consistent significant increase in ω-gliadins with increasing drought stress. Higher levels of HMW glutenins and a reduction in LMW-C glutenins were observed exclusively under severe drought stress in German genotypes. The drought-induced compositional change correlated positively with the specific bread volume, and was mainly associated with an increase in ω-gliadins and with a slight increase in HMW glutenins. Despite the generally lower HMW glutenin concentrations of the Iranian genotypes and no effect of drought on the concentration of HMW sub-fraction, there was still high specific bread volume under drought. It is suggested that for the development of new wheat cultivars adapted to these challenging climatic conditions, the protein composition should be considered in addition to the yield and grain protein concentration.
Eco-physiological studies on False Horn plantain
(2020) Dzomeku, Beloved Mensah; Wünsche, Jens Norbert
West Africa suffers from climate uncertainty, high levels of variability, lack of access to real-time and future climate information, and poor predictive capacity are common barriers to adaptation though the region is identified as climate-change hotspot. The regions vulnerability is heightened by its overdependence on rain-fed agriculture, with its sensitivity to climate change and variability. Rain-fed agriculture contributes 30% of GDP and employs about 70% of the population, and it is the main safety net of the rural poor. Drought affects plantain production in West Africa resulting in high level of food insecurity among the vulnerable. Under rain-fed production, achievable yield of plantain landraces are 11.0t/ha while the potential yield is 20t/ha. Plantain breeding is limited due to the complex nature of the breeding process. Plantain plant itself is a giant herbaceous plant occupying 6m2 of land hence only 1667 could occupy a hectare of land. The production system is faced with a myriad of challenges from inadequate healthy planting materials at the time of plantain through the production system to post-harvest. Unlike bananas which are mainly produce by multinational companies under irrigation, plantain production is mainly by smallholder farmers under rain-fed agriculture. Whereas banana production under irrigation is efficient, plantain production under rainfed production is haphazard and unsustainable. Farm sizes range between 0.4 to 5ha. Major limiting factors of the rainfed system is drought resulting in low yields and economic loses. Our study seeks to understand the effects of drought on the physiological responses of plantain crop under rainfed production. Different experiments were conducted to study the responses of various cultivars to on-farm rapid production of healthy planting materials. The results revealed that drought seriously affects natural regeneration of plantain planting materials as such new approaches need to be used for sufficient production. As each plantain plant produces averagely 42 leaves before flowering and each leaf has at least one axillary bud, it presupposes that 42 suckers should be produced at harvest. However, at harvest only 12 healthy suckers are produced around each plantain plant. The approach is able to exploit the full potential of every sucker to generate healthy planting materials. This technique therefore could be used to set up commercial propagation system for plantain planting material production. The study revealed Apantu and hybrid plantain FHIA-21 to show same responses. Plantain farmers can easily produce in large quantities healthy plantain planting materials using sawdust and building their own humidity chambers near water source. The study also showed that there is the potential for farmers to use this technique for establishing commercial propagation centres to generate healthy planting materials. We also studied the physiological responses of Apantu crop to water regimes and natural mycorrhization of plantains. Also, study was conducted on the fruit maturity index and the effect of climate variability on fruit micronutrient content. The natural mycorrhization of plantain roots was the first to be reported on plantain in Ghana. During the study it was observed that plantain roots were naturally colonised by mycorrhizae. However, this phenomenon was cultivar specific; with Apantu roots more colonised compared to Apem. Sustainable intensification of plantain production could be achieved through the use of beneficial soil microbes in production. Conventional production systems, however, do not promote the survival of these microbes. The study further revealed that plantains respond to water stress by reduction in stomatal density, movement and reduction in leaf area. In addition, early stages of water stress had little effect on the final yield of the crop. The anatomical and physiological studies were challenges faced in laticiferous plant like the plantain. However, drought stress at advance stage of growth of plantain adversely affect yields. Our study also showed that fruit maturity index could vary with seasons. The various maturity indices used in plantain production could not be used under rain-fed conditions; especially angularity. The angularity index used was observed not to be appropriate in the dry season. The study also revealed high α-carotene levels with seasonality and maturity in plantain. The high levels of provitamin A in plantain fruits during the dry season coincided with high incidence of sun’s UV index. This finding could play a significant role in the plantain industry as a food security crop the vulnerable who could not afford the high provitamin A foods especially for children under five years. However, the retention and bioavailability of the carotenoid after cooking need to be studied. In conclusion all the chapters showed clear understanding of the behaviour of plantain under severe adverse environmental conditions and conclusions drawn to guide future production of the crop. Under climate change with its complexities, further studies on plantain is needed to improve productivity to achieve food security in West Africa.
Genotypic responses of rice to alternate wetting and drying irrigation in the Mekong Delta
(2023) Johnson, Kristian; Vo, Thuong Ti Bach; Van Nha, Duong; Asch, Folkard
In the Vietnamese Mekong Delta (VMD), alternate wetting and drying (AWD) in rice (Oryza sativa L.) production during the dry season has the potential to reduce greenhouse gas emission and freshwater use. However, its effect on yield compared with continuously flooded systems can vary. To evaluate the effect of AWD on yield and yield‐forming processes on genotypes commonly grown in the VMD, field trials over two consecutive dry seasons were conducted at the Loc Troi Group's agricultural research station in the VMD. We observed a significant yield reduction, 7% on average, across all varieties grown under AWD. Analysis of yield components showed that under AWD, genotypes on average produced more tillers, but fewer spikelets, suffered greater spikelet sterility and had a lower 1000 grain weight. The size of this effect differed between dry seasons. Accordingly, we were able to identify and characterize genotypes better suited to AWD. We also could relate shifts in sink‐source relationships to the overlap of drying events and key phenological stages other than flowering. Our study shows how successful implementation of AWD requires adaptation to both environment and genotype.
Identifizierung und Quantifizierung von Trockenstressreaktionen an ausgewählten Zierpflanzenkulturen
(2013) Krato, Theresa; Wünsche, Jens Norbert
The present thesis gives attention to the development of a practicable screening process for the identification of drought-stress tolerant ornamental plants. Requirements are to be created in terms of reduced water use, market expansion to warmer regions and increased ability of transportation. The studies were included into a cooperative research project involving 4 plant breeding companies, research centre Jülich, research institute Geisenheim and the GFP. Scope of the thesis was the deployment and evaluation of an assessment scheme to quantify drought-stress reactions, the development of dehydration experiments under stationary climatic conditions and to search for physiological markers of drought-stress tolerance. The experiments were mainly conducted on Petunia Cultivars and Impatiens Neu Guinea Grp. Genotypes. Main results of the investigation are listed below: 1. The species specific assessment schemes are based on an accurate visual characterization of the wilting process. The wilting is rated using ranks from 1 ? 9. Assessed parameters were the phyllotaxy, surface texture and leaf color. The assessment schemes were proved to be acceptably objective and precise during the experiments and the genotypes were evaluated accordingly. 2. The plants were dried out under standardized conditions in climate chambers. The decrease of water as well as the occurrence of wilting was recorded. Climatic conditions (temperature, humidity and radiation) in dehydration experiments were set up to reach a rank of 9 in 5 to 9 days according to drought-stress tolerance and pretreatment of genotypes. For this reason, an adequate differentiation between genotypes was ensured even with a single assessment per day. However, the system weight (substrate and plant), which was used to characterize the stress intensity has to be corrected about the fresh weight of plants. The investigated genotypes of Impatiens behaved similarly regarding to their drought-stress tolerance in many replications and consequently allowed for a ranking. In contrast, the ranking order of investigated genotypes of Petunia was vague in experimental replications. However, an influence of water supply on the wilting behavior of plants was detected in this context. 3. In order to search for physiological markers of drought-stress tolerance, studies on water potential, gas exchange and thermal imaging were conducted in line with the dehydrogenation experiments. A tendency was shown, that drought-stress tolerant genotypes reacted later and less distinctive on drying of the substrate compared to susceptible plants. But a correlation between water potential of shoots and water supply in the substrate as well as a differentiation between genotypes was certainly week. This was mainly due to high variation of data. The transpiration rate of investigated plants reacted more on water supply though. The ranking, which was based on the parameter transpiration rate correlated well with the ranking of the wilting behavior from the dehydrogenation experiments. Consequently, the stomata management appears to be a promising indicator of drought-stress tolerance. Thermal imaging showed an increase of leaf temperature with decreasing moisture content of the substrate. Accordingly, the leaf temperature of Impatiens can serve as an indicator for the opening rate of stomata. 4. Currently, the dehydrogenation experiments can be considered as the easiest and most practicable approach to identify drought-stress tolerant genotypes of Impatiens and Petunia due to the results of the present thesis. Physiological measurements supported the ranking of genotypes, which was developed according to the dehydrogenation experiments. Especially, data on the opening rate of stomata illustrated differences between the tested genotypes. However, the dehydrogenation experiment does not provide information of the dependence of vegetative and generative performance of plants on water supply, which is very important for producers of ornamentals. 5. The ranking of drought-stress tolerance from climatic chambers corresponds only partly with results of experiments under field conditions. Therefore, a screening concept has to be developed in a subsequent project to investigate the complex context of climate-stress tolerance.
Managing crop health by mineral nitrogen fertilization and use of different chemical nitrogen forms
(2023) Maywald, Niels Julian; Ludewig, Uwe
Maintaining plant health is one of the most difficult but crucial challenges in crop production to realize plants’ full genetic potential. It is lowered by a variety of abiotic and biotic stresses that are becoming more severe and unpredictable due to climate change and its consequences. In addition, the use of chemical synthetic pesticides is increasingly criticized for endangering sensitive natural resources and possible pesticide residues in food and environment. Avoiding or reducing the use of chemical synthetic plant protection products makes the control of phytopathogenic pests even more difficult. Therefore, in addition to optimizing various management measures such as tillage, sowing time, row spacing or crop rotation, mineral nitrogen (N) fertilization and the targeted application of N forms must be utilized to reduce abiotic stress factors and the infestation pressure of certain pests to ensure high yield performance. Consequently, several experiments were conducted to better understand how mineral nitrogen fertilization and forms can improve plant health by increasing plant resistance to abiotic stressors, particularly repeated drought stress and nutrient (P) deficiency, and to biotic stressors, such as relevant phytopathogenic fungi. It was found that with respect to repeated drought stress, maize plants receiving supplemental nitrogen during the recovery period after an early drought stress were better able to cope with late drought stress. In this context, N fertilization could help the plant to maintain its photosynthetic activity under drought stress. Additionally, plants repeatedly exposed to drought stress recovered faster with N fertilization due to transiently higher antioxidant levels and higher production of reactive oxygen species. A further experiment revealed that depending on the maize genotype, ammonium as a form of nitrogen has a positive effect on the availability and uptake of phosphorus compared to nitrate, depending on the maize genotype. This observation could be attributed not only to the acidifying effect on the pH of the rhizosphere, but also to the increased abundance of various phosphorus-solubilizing bacteria and arbuscular mycorrhizal fungi under ammonium nutrition. Together this could provide an enhanced P availability, which ultimately reduces plant stress and improves physiologically resistance leading to a reduction in disease risk. Nevertheless, studies revealed that high N fertilization in most cases promotes disease attack and makes the plant more susceptible to pathogens. Scrutinization of this observation indicated that N fertilization enhances infestations of biotrophic pathogens, especially in wheat, while necrotrophic fungi were attenuated. Overall, the complex relationship between plant pathogens and nitrogen nutrition appears to be highly variable due to dynamic factors such as the soil, microorganisms in the rhizosphere, environmental factors, and the host plant, making it difficult to give definite statements about the effects of nitrogen nutrition on pathogen occurrence. Thus, the form of nitrogen could be a promising way to target nitrogen fertilization against individual pathogens. With regards to the previous research, experiments on the influence of N form on pathogen infection, revealed that wheat leaves inoculated with the foliar pathogen Blumeria graminis f. sp. tritici (Bgt) were comparatively less infested when fertilized with nitrate or cyanamide compared to ammonium. After contact with the pathogen, an enhanced defense response in form of increased production of protective substances, indicated by increased concentrations of hydrogen peroxide and superoxide dismutase, and increased antioxidant potential, was detected. Further, it was observed that ammonium fertilization resulted in lower bacterial richness in the plant rhizosphere and higher fungal richness compared to nitrate supplementation. Additionally, a pronounced effect of ammonium fertilization on rootcolonization by important fungal pathogens such as Gaeumannomyces graminis var. tritici (Ggt) and Bgt was found. Regarding the experiment with maize under low P conditions, it appears that ammonium is able to promote both pathogenic and beneficial fungi in cereal crops. Thus, nitrate fertilization appears not only to suppress the occurrence of fungi, but may also promote pathogen-antagonistic bacteria, which in turn have a positive effect on fungal disease suppression.
Optimizing selection efficiency in maize for the drought prone eastern and southern African environments
(2013) Kebede, Aida; Melchinger, Albrecht E.
Breeding for stress tolerance is the most cost effective way of avoiding drought-induced yield reduction in the tropics. Optimizing breeding for drought tolerance at CIMMYT could enhance the effectiveness of this multi-national breeding program and warrant fast delivery of drought tolerant materials to the farmers. Thus, the overall aim of my study was to improve the efficiency of drought tolerance breeding of maize at CIMMYT for the rapid and cost effective advancement of drought tolerant materials for the drought prone regions of the ESA (Eastern and Southern African countries). We screened a diverse source of tropical germplasm for their haploid induction rate (HIR) and the seasonal variation of this trait. We then compared various managed drought and well watered experiments conducted as line per se performance trials (LP) and testcross performance trials (TP) in Kenya and Mexico. Further, we estimated the relative selection efficiency of the principal breeding regions of CIMMYT for the tropics in ESA and Mexico with unselected and selected breeding materials. The specific objectives of my study were to (1) monitor the variation for HIR among diverse source germplasm in tropical maize, (2) determine the relative importance of general (GCA) and specific (SCA) combining abilities of the source germplasm for HIR, (3) investigate the influence of tropical summer and winter seasons and genotype × season interactions on this trait, (4) determine if LP is predictive of TP for yield under drought in sets of lines under development by the CIMMYT maize breeding program in Kenya and Mexico, (5) determine the genetic correlation between performance of lines per se under drought and testcrosses under optimal conditions and assessing its effect on yield potential, (6) examine the correlation between TP under well-watered and drought stress conditions for potential indirect selection efficiency of well-watered conditions in comparison with drought stress, (7) determine the relative importance of regional adaptation of maize hybrids to Mexico and ESA by subdividing the genotype × environment interactions and determining genotypic correlations between both regions, (8) calculate the indirect selection efficiency for selecting materials based on test results from one region on the selection gain in the other region, and (9) identify the most suitable stage for exchanging breeding materials between Mexico and ESA. Source germplasm and induction season affected HIR and MCR (mis-classification rate) considerably in tropical maize. Source germplam with high HIR and low MCR could be used in the initial stage of implementing the DH technology in the tropics. GCA effect was more important than SCA or genotype × season interaction effects for HIR in tropical maize. Thus, enhancing HIR in source germplasm can be achieved through cyclical breeding or recurrent selection. Winter season was considered the best season for induction because it provides suitable environmental conditions for higher HIR and lower MCR. Overall HIR was high enough to apply the in vivo DH technology in the routine breeding activities in tropical maize. There were moderate genotypic correlation and ISE (Indirect Selection Efficiency) values between LP and TP under drought that increased with an increase in stress level. Hence, LP trials were predictive of TP trials particularly under severe drought stress. Furthermore, screening of lines for LP under drought stress did not compromise yield potential. TP under well-watered conditions were not predictive of TP under drought stress emphasizing the need of managed drought trials to identify drought tolerant materials. With the current shift of inbred development to large scale DH line production, LP evaluations can reduce the cost of making large numbers of testcrosses and optimize breeding for drought tolerant hybrids in the tropics. The exchange of breeding materials between ESA and Mexico can be done with early and late generation materials. This is because there was negligible genotype by region interactions as compared to genotype by location interactions within each region and high genotypic correlations between the two regions. Further, ISE estimates for trials conducted in Mexico and in ESA were high. Adaptive diseases for each location might hamper the exchange of materials, however, with current molecular marker tools like marker assisted selection and genomic selection, the problem of selecting for disease resistance in the region where the disease is not prevalent seems promising. In conclusion, there are ample opportunities in the CIMMYT maize breeding program to optimize breeding for drought tolerance in the tropics through rapid and large scale production of DH lines and evaluation of these lines for LP in managed drought trials. Moreover, breeders from ESA and Mexico could benefit from each other?s materials and test results by regular exchange of breeding materials at both the early and late stages of testing.
Phenotypic and molecular analyses of grain and biomass productivity under irrigated and rainfed conditions in hybrid rye
(2014) Gottwald, Marlen; Miedaner, Thomas
Rye (Secale cereale L.) is a small grain cereal used for bread making, livestock feeding and as renewable energy source. These types of usages are leading to different breeding goals. Rye growing regions are affected by climate change and consequently by drought. Germany is touched by rainless periods in spring and early summer in the last years. Again, in spring 2012 farmers in Brandenburg and Lower Saxony were affected by drought periods. Yield losses in those regions, especially in combination with sandy soils are expected. Therefore much attention is paid for breeding of drought resistant germplasm. Briefly, our objectives of this study were to (1) estimate the biomass and biogas potential of different plant materials, their quantitative genetic parameters and biogas-related traits, (2) analyze two recombinant inbred lines and differences in their yield potential between irrigated and rainfed regime, as well as the relative efficiency for indirect selection for drought resistance in irrigated regime, and (3) investigate the phenotypic performance for ten agronomic and quality traits across multiple environments and estimated the number and effects underlying QTL. For the biomass-/ biogas analyses a wide range of plant material was analysed. Germplasm resources, full-sib families selected for grain and forage use were tested for their per se and testcross performance and experimental hybrids selected for grain use and population cultivars selected for grain and forage use were analyzed. Dry matter yields varying across environments from 106 to 177 dt/ha for per se and testcross performance, respectively. For testcross performance, germplasm resources showed similar values to forage rye. The later the maturity stage, the more dry matter yield on the whole plant level was achieved. Estimates of genotypic variances for biomass yield were significant for all rye materials, whereas the variances per se and for testcrosses were for germplasm resources exorbitant higher than for forage and grain rye. Typical cumulative methane production curves were obtained for the whole plant material from the Hohenheim biogas yield test. Methane yield showed large differences between second and third harvest date for individual plant fractions. Differences between genotypes were not substantial for methane yield although significant in some instances. At EC77/83 hybrids and forage rye reached similar methane yield of about 5000 m3/ha. A high correlation between dry matter yield and methane yield was observed (r=0.95). Concerning high cost and time consuming analysis of biogas tests, for breeders the main breeding goal should be maximum dry matter yield. Direct selection on dry matter yield should indirect improve methane yield. Two biparental populations were used for the analysis of drought tolerance. The analysis was performed in duplicate. Both populations were grown under irrigated and rainfed regimes. Striking less rainfall compared to long-term precipitation occurred between April and July, during critical phases of plant development. Grain yield reduction between irrigated and non-irrigated regime ranged from 2% to 29.6% for population A and 2% to 40% for population B, whereas differences between both regimes were significant (P<0.05) for five and four environments, respectively. Genotypic variances of grain yield were significant in all instances, whereas genotype by irrigation interaction variance between both regimes being significant only in three and four environments for population A and B, respectively. Analysis across those environments revealed significant difference for genotype by irrigation interaction variance and the three-way interaction variance in both populations. Heritability estimates were higher for the irrigated than for the rainfed regime. High interaction variance with environment and no clustering of the two regimes in a multi-dimensional analysis were found. This illustrates the different soil and whether conditions between locations and additionally every location suffered from a different drought stress. The correlation between both regimes was significant but moderate, but genotypic coefficients considerably higher (Pop-A: 0.86, Pop-B: 0.84), which could be substantiated that testcrosses differed not substantially in drought-resistance. Indirect selection for drought in the irrigated regime was predicted to be equally or more efficient than direct selection in the non-irrigated regime. Phenotypic and genotypic analysis was done across ten environments for both biparental populations for the general improvement of agronomic and quality traits in rye. Population A were genotyped with a Rye5K SNP array and for population B DArT genotyping was done with a 3K rye array. Additionally both populations were genotyped with about 150 SSRs. The genetic linkage maps comprised 1,819 and 1,265 markers for population A and B, respectively and were used for the QTL analysis for ten agronomic and quality traits. Phenotyping revealed large genetic variation for ten agronomic and quality traits. Intensive phenotyping at up to ten environments led to moderate to high heritabilities. Across environments explained genotypic variance of the individual QTL ranged from 5 to 55%. For 1000-kernel weight, test weight, falling number, and starch content, several QTL with high effects and a frequency of recovery of about 90% were identified in both population. Rye suffered from drought stress in the last decade. Focusing on general improvement of rye regarding yield and quality, as well as improving rye regarding drought-resistance is important. Future research should be done in fine mapping and validation of the detected QTLs, for exploiting their potential in marker assisted breeding.
Quality impact of nitrogen in wheat grain properties and protein development for higher baking quality
(2022) Rekowski, Azin; Zörb, Christian
Storage protein concentration and composition influence the baking quality of wheat. Traditionally, baking quality is correlated with the total protein concentration in flour. However, despite similar protein concentrations, the baking qualities of different cultivars can vary, and the variances may be related to differences in the storage protein composition (Zörb et al., 2018). Though both protein concentration and composition are affected by fertilization management (especially nitrogen) and water availability, it is not certain whether compositional changes will suffice to enhance the quality of final products. Additionally, there is a high risk for the environment, associated with nitrogen losses in wheat production. To increase nitrogen efficiency, minimize nitrogen losses and optimize the baking quality, it is crucial to improve nitrogen fertilizer management. To address the question whether nitrogen and water management induce changes in protein composition which result in altered baking qualities, several investigations were conducted in the present work. Total protein was extracted from wheat flour and SDS-PAGE (Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis) was used to detect proteins sub-fractions. To assess baking quality, the specific volume, freshness retention as well as the hardness of the bread were evaluated. In chapter two, as part of a pot experiment, two different levels of late nitrogen fertilizer were tested using two winter wheat cultivars of different quality classes (Discus and Rumor). Both cultivars produced more grain yield and total protein concentration as a result of late nitrogen supply. However, bread volume was only increased in Discus, possibly related to the greater changes in total gluten concentration and protein composition including HMW-GS and ω-gliadins. However, an increase of late nitrogen level did not further improve baking quality. Compared to Discus, an addition of late nitrogen did not result in significant changes in the protein composition of Rumor. Collectively these results indicate that late nitrogen management strategies are practical but need to be adjusted depending on the cultivar used. Chapter three describes a field experiment where three different nitrogen forms were used ((i)ammonium nitrate, (ii) urea with 46% total N, (iii) urea as before amended with urease inhibitor N-(2-nitro-phenyl) phosphoric triamide (2-NPT) and (iv) control (no nitrogen addition)). While no significant/only a slight effect was observed for urea alone, ammonium nitrate and urea plus urease inhibitor similarly increased total grain protein concentrations. Although both fertilizers boosted the levels of ω-gliadins and HMW-GS among the storage protein fractions, the influence was more pronounced in the ammonium nitrate application. In comparison to the urea treatment, the combination of urea plus urease inhibitor significantly influenced protein composition and generated higher specific baking volumes and the best fresh-keeping characteristics. Due to the strong enhancement in NUE and baking quality obtained with the urea plus urease inhibitor application, accompanied by reduced nitrogen losses and easy handling, this treatment could be considered as a substitute for urea alone or ammonium nitrate. Chapter four describes a field study conducted in Iran with different German (Impression, Discus, Rumor, Hybery) and Iranian (Alvand, Mihan) genotypes representing diverse quality classes and grain protein levels. Two different levels of water stress were applied during anthesis and grain filling period. Overall, no significant changes in total protein concentrations were recorded. In addition, the concentrations of different protein fractions were unchanged in five out of the six genotypes. However, German genotypes exhibited an increase in HMW-GS under severe drought conditions, and an increased severity of drought stress amplified the percentage of ω-gliadins in all genotypes. Even though drought stress did not alter the concentrations of the HMW-GS sub-fraction in Iranian genotypes, a high specific bread volume was still observed, most likely related to an increase in ω-gliadins. All in all, the protein composition should be considered in addition to yield and total grain protein concentration when developing new wheat varieties for challenging climatic conditions. In summary, late nitrogen and urea application, along with the addition of urease inhibitors, can enhance the gliadin and glutenin content and improve the baking quality. In addition, it may be possible to develop wheat genotypes with optimal baking properties by paying attention to the protein composition when drought stress exists. Although genetically determined subunits of the gluten fractions are known to be associated with bread-making quality, the studies presented here indicate that additional factors, such as the levels of nitrogen supply or water limitation, affect the composition of grain protein fractions and can be positively correlated with baking quality. Therefore, total grain protein concentration alone is not a reliable indicator of grain quality. Additionally, several individual proteins were altered by different management practices. Consequently, these proteins can have great effects on the quality of breads, so further studies should evaluate whether those individual proteins directly correlate with bread baking quality.
Rye (Secale cereale L.) : agronomic performance under drought and methods of crop physiology to determine the drought tolerance of winter rye
(2015) Kottmann, Lorenz; Fangmeier, Andreas
Winter rye (Secale cereale L.) is predominantly cultivated on light and sandy soils with a low water holding capacity and will therefore be especially affected by drought induced yield losses in Central and Eastern Europe in the future. Drought adaption through breeding is therefore an important task in order to adapt this crop to future climate conditions. In this context, the crop physiology methods canopy temperature depression (CTD = Tair - Tcanopy) and carbon isotope discrimination (delta) were examined for their suitability as selection criterion under drought on a small number of genotypes. Two sets of each 16 genotypes were therefore grown under different drought conditions in rain-out shelters and under well-watered conditions in the years 2011, 2012, and 2013. The CTD was determined several times during the growth period using two infrared (IR) thermometers and an IR camera. delta-analyses were performed on mature flag leaves (delta_leaf) and grains (delta_grains). Furthermore, ash content in mature flag leaves and grains, as well as mineral concentrations in mature flag leaves (Ca, K, Mg, and Si) were examined for their use as surrogates for the expensive and time-consuming delta-analyses. In addition to the evaluation of possible selection criterions, the agronomic performance of rye in the different drought regimes was assessed: Grain-, straw-, and total aboveground biomass yields, the grain yield components spikes m-2, kernels spike-1, and thousand kernel weight (TKW), leaf area index (LAI), and phenological characteristics were examined. Drought induced grain yield reductions ranged from 14 to 57%, whereas straw yield was generally lesser affected. The growth period was shortened by up to 12 days under drought conditions compared to optimal water supply. Grain yield was positively associated to straw yield, LAI, spikes m-2, and kernels spike-1 under water deficit. High number of grains per area land seemed to be especially important for high grain yields under drought. Furthermore, the results suggest a strong importance of pre-anthesis reserves for the reallocation of assimilates for grain filling under drought in rye. Regarding the suitability of possible selection criterions, CTD was significantly positively related to grain yield under drought. Significant correlations between CTD and grain yield were, however, only observed when the measurements were carried out on days with optimal weather conditions. Optimal conditions turned out to be days with a clear sky, a solar irradiation >700 W m-2, an air temperature of at least 20°C, as well as wind speeds <3 m s-1. Furthermore, the results showed that also rather inexpensive IR instruments are suitable to assess the CTD. Regarding the carbon isotope discrimination, delta_leaf was significantly positively related to grain yield under water deficit, but the correlation was weaker than between CTD and grain yield. Delta_grains was not related to grain yield at all. Ash content and mineral concentrations were significantly related to grain yield under drought, but the correlations were quite inconsistent between the two experimental years. Because of the weak or missing relationship with grain yield, carbon isotope discrimination and its potential surrogates ash content and mineral concentration cannot be recommended for their use as selection criterions under German climate conditions at present. A general limitation of the preset work was, however, the low genetic variability of the genotypes, which may have reduced the significance of the results. The results should therefore be validated with a more diverse set of genotypes. However, especially the CTD seemed to be a promising selection criterion which may help to develop drought tolerant rye genotypes, if this method can be successfully integrated into the breeding process.
Varietal effects on Greenhouse Gas emissions from rice production systems under different water management in the Vietnamese Mekong Delta
(2023) Vo, Thi Bach Thuong; Johnson, Kristian; Wassmann, Reiner; Sander, Bjoern Ole; Asch, Folkard
Rice production accounts for 15% of the national Greenhouse Gas (GHG) emissions and Vietnam aims at reducing emissions from rice production by focusing on changing farming practices. However, the potential for mitigation through the selection of different rice varieties is still poorly understood. A two‐year field screening of 20 rice varieties under continuous flooding (CF) and alternate wetting and drying (AWD) irrigation was conducted in the Vietnamese Mekong Delta (VMD), Vietnam, employing the closed chamber method for assessing GHG emissions. The results confirmed that varietal variation was the largest for methane (CH4) emissions under CF. Across the varietal spectrum, CH4 emissions were more important than nitrous oxide (N2O) (accounts for less than 2% of the CO2e) with the lowest emitting variety showing 243 kg CH4 ha−1 and the highest emitting variety showing 398 kg CH4 ha−1 emissions as compared to 0.07 kg N2O ha−1 and 0.76 kg N2O ha−1 emissions, respectively. Under AWD, CH4 emissions were generally strongly reduced with the varietal effect being of minor importance. Compared with IPCC default values, the data set from the two seasons yielded higher Emission Factors (EFs) under CF (2.92 and 3.00 kg ha−1 day−1) as well as lower Scaling Factors (SFs) of AWD (0.41 and 0.38). In the context of future mitigation programs in the VMD, the dry season allows good control of the water table, so varietal selection could maximize the mitigation effect of AWD that is either newly introduced or practised in some locations already. In the wet seasons, AWD may be difficult to implement whereas other mitigation options could be implemented such as selecting low‐emitting cultivars.