Browsing by Subject "Abiotic stress"

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Characterization of epidermal bladder cells in Chenopodium quinoa
(2021) Otterbach, Sophie L.; Khoury, Holly; Rupasinghe, Thusitha; Mendis, Himasha; Kwan, Kim H.; Lui, Veronica; Natera, Siria H. A.; Klaiber, Iris; Allen, Nathaniel M.; Jarvis, David E.; Tester, Mark; Roessner, Ute; Schmöckel, Sandra M.
Chenopodium quinoa (quinoa) is considered a superfood with its favourable nutrient composition and being gluten free. Quinoa has high tolerance to abiotic stresses, such as salinity, water deficit (drought) and cold. The tolerance mechanisms are yet to be elucidated. Quinoa has epidermal bladder cells (EBCs) that densely cover the shoot surface, particularly the younger parts of the plant. Here, we report on the EBC's primary and secondary metabolomes, as well as the lipidome in control conditions and in response to abiotic stresses. EBCs were isolated from plants after cold, heat, high‐light, water deficit and salt treatments. We used untargeted gas chromatography–mass spectrometry (GC–MS) to analyse metabolites and untargeted and targeted liquid chromatography‐MS (LC–MS) for lipids and secondary metabolite analyses. We identified 64 primary metabolites, including sugars, organic acids and amino acids, 19 secondary metabolites, including phenolic compounds, betanin and saponins and 240 lipids categorized in five groups including glycerolipids and phospholipids. We found only few changes in the metabolic composition of EBCs in response to abiotic stresses; these were metabolites related with heat, cold and high‐light treatments but not salt stress. Na+ concentrations were low in EBCs with all treatments and approximately two orders of magnitude lower than K+ concentrations.
Drought affects the synchrony of aboveground and belowground phenology in tropical potato
(2023) Hoelle, Julia; Khan, Awais; Asch, Folkard
The literature describes the belowground and aboveground phenology of potato to be linearly related. Bud formation is synchronous with tuber initiation and flowering with tuber filling. Many agronomic and breeding studies on potato use non‐destructive aboveground phenology to assess belowground development. No information is currently available on the influence of water deficit on the synchrony of above‐ and belowground development in potato. Five contrasting potato genotypes were subjected to four irrigation treatments on two different soil types. The irrigation treatments were as follows: fully watered, early drought, intermediate drought, and late drought. In 5‐day intervals after withholding water, detailed belowground and aboveground development was recorded. Results showed that the synchrony between aboveground and belowground development is strongly influenced by both water deficit and development stage at drought initiation. Under early drought, the aboveground development was hastened and belowground development was delayed. The opposite was found in later development stages. The earlier the drought was initiated, the longer the tuber filling phase was, while the bulking phase was shortened. We concluded that under terminal drought conditions aboveground development and belowground development need to be evaluated separately and cannot follow the standard evaluation system that uses aboveground phenology as a proxy for tuber formation belowground development rates.
Environmental effects on physical properties of Geohumus and effects of its application on drought responses in maize
(2013) Duong, Van Nha; Asch, Folkard
Geohumus belongs to a new generation of soil melioration/hydrophilic polymers; however, evidence is limited with regard to both, the ability of Geohumus to store water in variable abiotic environments and the effects of Geohumus or other hydrophilic polymers on plant genotypes in response to drought condition. Therefore, this study aims at providing necessary and complementary information for improving Geohumus usage under field condition, and to improve our ecophysiological understanding of the interactions between Geohumus, plant genotype and the growing environment. Three series of experiments were conducted to investigate (1) how abiotic factors affect the water holding capacity and restorability of Geohumus, (2) how the application of Geohumus affects plant morphological and physiological traits in response to different irrigation scenarios such as full irrigation, water deficit, and re-watering and (3) how the application of Geohumus in different soil types affects drought induced plant root-shoot communication. Water holding capacity (WHC) and restorability of Geohumus in mL water g-1 was determined by immersing teabags with fresh and used Geohumus in prepared media under laboratory conditions. A greenhouse experiment was carried out in order to analyze morphological and physiological responses of the two maize cultivars Mikado and Companero to progressive drought or full irrigation (field capacity) as affected by Geohumus. To obtain in depth information on Geohumus-plant interactions, a split root system experiment was conducted as a tool to investigate hydraulic and bio-chemical root-shoot communication of Mikado and Companero under full irrigation, partial rootzone drying, and deficit irrigation. Our results showed a negative correlation between salt concentration and water holding capacity (WHC) of Geohumus due to replacement of water molecules by ions at the polarized sites within the polymer chain (James and Richards 1986). Furthermore, salt types affected the WHC of Geohumus differently; in particular, multivalent ions were stronger impeding Geohumus compared to monovalent ions. Consequently, Geohumus application to sandy soil with base fertilizer application or to compost could not improve soil water content. However, split fertilizer application to sandy soil containing Geohumus led to a significantly improved soil moisture content indicating that timing and amount of fertilizer should be carefully considered under Geohumus application. Furthermore, for field applications the effect of climate needs to be considered, since the WHC of Geohumus increased with increasing temperature. The preferential ion uptake of Geohumus could translate into competition with plant roots for nutrient uptake from soil solution. On the other hand, Geohumus can capture nutrients which might have been lost for plants due to drainage. We found indications of these positive effects since biomass and leaf area of Mikado and Companero maize genotypes were increased compared to soils without Geohumus. Theoretically, polymers could release stored water to plants under drought stress; which in turn could inhibit or delay chemical signaling. However, our results showed increased concentrations of [ABA]leaf and [ABA]xylem of both Mikado and Companero grown in sandy soil with Geohumus in response to drought compared to treatments without Geohumus. This hormonal response was associated with larger leaf area and greater biomass resulting in a higher plant water demand due to its increased transpiration area while Geohumus did not improve soil water content significantly. On the other, hand root/shoot ratio, absolute root length and root biomass were decreased in plants grown with Geohumus. This suggests that plants grown with Geohumus under drought conditions could not extract water from deeper soil layers. The split root experiments showed that the larger leaf area of plants grown with Geohumus in combination with limited moisture content of sandy soil resulted in a stronger chemical root-shoot signal related to water stress. Regardless the increased [ABA]xylem which is associated with a reduction of stomatal conductance, Geohumus application could result in a decreased leaf water potential under partial root zone drying. Mikado grown with and without Geohumus, as a genotype potentially adapted to drought conditions, was able (1) to maintain its water potential under water limited conditions by penetrating roots into deeper soil layers (2) to delay the expression of physiological traits associated with drought, and (3) to maintain its shoot weight in contrast to Companero, a drought sensitive cultivar. The presented results are of relevance for the improvement of our understanding of the impact of abiotic factors such as temperature, salt concentration, and salt types on the WHC of Geohumus and therefore will help to optimize the application of hydro-gels under field conditions. Beneficial traits of plant genotypes grown under Geohumus application were identified, which will be valuable for breeding and applied programs targeting at crop improvement in arid and sub-arid regions and areas vulnerable to climate change.
Genotype specific responses to Bacillus spp. inoculation in lowland rice (Oryza sativa L.) under iron toxicity
(2023) Weinand, Tanja; Asch, Folkard
Amidst a growing global population, limited arable land, and higher pressure from both abiotic and biotic stressors in a shifting climate, there is a need for enhancing yields through sustainable agricultural practices, and new, more tolerant cultivars. In recent decades, employing microbial inoculants as biofertilizers and biopesticides has gained growing popularity. Yield reductions ranging from 16-78%, and sometimes complete crop failure, can occur in in lowland rice cultivation systems where high iron concentrations in the soil solution lead to excess iron uptake by the plants. Twenty to 60% of the rice growing area of sub-Saharan Africa is affected by iron toxicity. Development of iron-tolerant cultivars has lagged, largely due to gaps in understanding the genotypic adaptation mechanisms to this stress. Furthermore, effects of the microbiome on such stress responses are often overlooked. Although there have been previous reports on growth promoting effects of bacteria inoculation in lowland rice under iron toxicity, these studies were focused on plant growth promotion and mineral nutrient uptake. The primary aim of this dissertation was to assess the effects of Bacillus spp. inoculation on different lowland rice cultivars under iron toxicity, with emphasis on genotypic shoot tolerance strategies. Physiological, biochemical, and molecular mechanisms underlying genotypic responses to Bacillus inoculation were investigated and potential overlaps with responses to biotic stressors explored. Within the framework of this dissertation, three lowland rice cultivars, were inoculated with three Bacillus isolates (two B. pumilus isolates, one B. megaterium isolate) and exposed to 1000 ppm Fe2+ in the nutrient solution. The three cultivars were selected because they differ in their tolerance against iron toxicity, with one being sensitive, one a tolerant excluder (tolerance through minimizing iron uptake), and one a tolerant includer (tolerance of high iron concentrations in the plant). At day eight of stress exposure, the effects of Bacillus inoculation on tolerance against iron toxicity were evaluated by leaf symptom scoring. The effects of bacteria on the progression of leaf bronzing were then related to specific tolerance mechanisms, such as shoot iron content, iron allocation within the shoot, ROS scavenger enzyme activity, and the expression of genes related to iron toxicity tolerance. Furthermore, the effects of inoculation on brown spot disease development seven days after infection with Bipolaris oryzae were also assessed by leaf symptom scoring. All three Bacillus isolates were characterized for their ability to solubilize Zn and P, production of auxin, siderophores, and HCN, the presence of ACC deaminase activity, and in vitro inhibition of fungal growth. Effects of Bacillus inoculation on iron toxicity tolerance were found to depend on the cultivar x Bacillus isolate combination. While leaf symptom expression was ameliorated in the inoculated sensitive cultivar, the tolerant excluder cultivar generally developed stronger symptoms of iron toxicity when inoculated with Bacillus. No significant effects of Bacillus inoculation on the tolerance against iron toxicity were found in the tolerant includer cultivar. The beneficial outcomes of bacterial inoculation on plant stress tolerance are often credited to the bacteria's plant growth promoting properties. However, we did not find a clear association between plant growth and tolerance to iron toxicity. Furthermore, the Bacillus isolates did not display ACC deaminase activity nor the ability to solubilize Zn or P. Auxin production was only notable in B. megaterium, the isolate with least effects on both tolerance to iron toxicity and brown spot disease development. Siderophore production was found in B. pumilus D7.4 but only under low iron supply. Instead of plant growth, iron homeostasis as well as the interconnection between iron homeostasis and the immune response of lowland rice seem to be affected by bacterial inoculation. For the first time it was shown that Bacillus inoculation can directly affect tolerance against iron toxicity in lowland rice through inducing the production of ferritin in the young leaf blades of the sensitive cultivar. NO produced by B. pumilus Ni9MO12 is hypothesized to be involved in the signaling cascade leading to OsFER expression. Activity of ROS scavenger enzymes of the ascorbate-glutathione redox cycle were not affected by Bacillus inoculation in the leaf blades. In the tolerant excluder cultivar, an alteration in iron distribution within the shoot of B. pumilus Ni9MO12 inoculated plants, is assumed to cause the decline in tolerance. In conclusion, it was shown that Bacillus inoculation can influence iron toxicity tolerance in lowland rice. The results underline the significance of the interaction between rice genotypes and bacteria isolates. Furthermore, Bacillus inoculation did not promote plant growth, instead, distinct adaptation mechanisms within the shoot tissue were triggered to allow for increased tolerance of high iron concentrations in the leaves. The signaling cascades involved might be linked with biotic stress responses. Understanding such intricate mechanisms is vital for improving plant productivity. While inoculants composed of single microbial isolates may not meet the anticipated outcomes for practical application in sustainable agriculture, they offer a valuable laboratory tool for investigating genotypic plant tolerance to various abiotic and biotic stresses and the role of the microbiome within. New breeding approaches that consider genotypic traits essential for obtaining a beneficial microbiome might accelerate the creation of more tolerant cultivars.
Physiological and growth responses of Jatropha curca L. to water, nitrogen and salt stresses
(2012) Rajaona, Arisoa Mampionona; Asch, Folkard
This thesis provides necessary and complementary information for an improved understanding of jatropha growth to guide further research to evaluate the response of jatropha to abiotic stressors and for designing plantations adapted to the plants? requirements. Given the fact that jatropha is claimed to grow on marginal lands, we studied effects of water supply, salt stress, nitrogen and air humidity as major abiotic stressors on gas exchange parameters and biomass production followed by management options for pruning the trees to positively influence biomass productivity and to contribute to optimize resource use. The effects of water availability (rainfed versus irrigated) on growth and gas exchange parameters were investigated for 4-year old jatropha grown in a semi-arid environment at a plantation site in Madagascar in 2010. The results confirmed that 1250 mm water in addition to a 500 mm rainfall did not affect biomass production and instantaneous gas exchange. Nevertheless, leaf light responses of irrigated plants were higher than that of rainfed plants. The study showed to what extent salt stress affected water use, canopy water vapour conductance, leaf growth and Na and K concentrations of leaves of 3-year old and young jatropha plants. 3-year old plants were exposed to seven salt levels (0-300 mmol NaCl L-1) during 20 days and young plants to five salt levels (0-200 mmol NaCl L-1) during 6 days. In both experiments, plants responded rapidly to salt stress by reducing water loss. The threshold value of responses was between 0 and 5 dS m-1. Leaf area increment of young jatropha had a threshold value of 5 dS m-1 implying that jatropha is sensitive to external salt application in terms of canopy development, conductance and CO2 assimilation rate. Transpiration of plants in both experiments was reduced to 55% at EC values between 11 and 12 dS m-1 as compared to non-stressed plants. These findings indicate that jatropha responds sensitive to salt stress in terms of leaf elongation rate and consequently canopy development, and to immediate physiological responses. Leaf gas exchange characteristics of jatropha as affected by nitrogen supply and leaf age were intensively studied, as carbon assimilation is one of the central processes of plant growth and consequently a key process embedded in modelling approaches of plant productivity. This study showed that N supply effects on leaf gas exchange of jatropha leaves were small with only the treatment without nitrogen resulting in lower rates of CO2 assimilation rate and light saturated CO2 assimilation rate, nevertheless, effects of N supply on biomass formation were pronounced. Instantaneous rates of leaf gas exchange of different leaves subject to variable air humidity (atmospheric vapour pressure deficit (VPD)) were investigated. This study showed that CO2 assimilation rate (A) and stomatal conductance (gs) were correlated in a hyperbolic fashion, and that gs declined with increasing VPD. Maximal stomatal conductance of jatropha was in the range of 382 mmol m-2 s-1 and gs is predicted to be close to zero at 6 kPa. Effects of VPD, via stomatal conductance, by preventing high transpiration rates, have been demonstrated to be decisive on water use efficiency. Our findings are in this regard relevant for the estimation of water use efficiency of jatropha. The outcome further indicates favourable conditions at which stomatal opening is high and thereby allowing for biomass formation. This information should be considered in approaches which aim at quantifying leaf activity of field-grown bushes which are characterized by spatially highly diverse conditions in terms of microclimatic parameters. Microclimatic parameters can be modified by the tree structure. The reported field experiment on 4-year old jatropha indicated that the biomass production and canopy size depended mainly on primary branch length. A comparison of plants of different pruning types with regard to trunk height (43 versus 29 cm) and total length of primary branches (171 versus 310 cm), suggest that higher biomass production and greater leaf area projection was realized by trees with short trunks and long primary branches. Growth of twigs and leaves was positively correlated with total length of branches. Relative dry mass allocation to branches, twigs and leaves, length of twigs per cm of branches and specific leaf area were not affected by pruning and water supply. Trees with shorter branches had a higher leaf area density. As opposed to an allometric relationship between the average diameter of primary branches and total above ground biomass, our data suggest that these traits were not constantly correlated. Our data indicate that the length of newly formed twigs, where the leaves are attached to, can be related to the total length of already established branches. Leaf area density and relative dry mass allocation to leaves were not affected by the two pruning techniques, indicating that pruning differences in leaf area size were proportionally converted to corresponding pruning differences in the canopy volume exploited by plants. The results reported in this study are relevant for understanding jatropha growth. It helps farmers first for a better plantation management and researchers as well as contribution to future modelling purpose concerning jatropha growth under variable climatic conditions. Additionally, it should complement information for a better set of priorities in research, contribute indirectly to breeding programs and adjust agricultural policies in terms of encountering global change.
Premature fruit drop in mango (Mangifera indica L.) in Northern Vietnam
(2011) Roemer, Malte G.; Wünsche, Jens Norbert
Mango production in Northern Vietnam is mainly organized in farmer-owned, small-scale orchard operations. However, the production is limited due to excessive fruit drop presumably caused by unfavourable climatic conditions in combination with plant stresses during the fruit set period. There is a general belief that this phenomenon is caused by different combinations of stressing factors which may vary between regions and sites. In the mountainous area of Northern Vietnam, fruit drop of two main local cultivars ?Hôi? and ?Tròn? may be caused by environmental cues occurring particulary during fruit set. Environemntal stress factors may include excessive air temperature, low relative humidity, strong prevailing winds and little rainfall. These multiple stressors are likely associated with a time dependent change of the endogenous plant hormone auxin (indole-3-acetic acid, IAA) exported from fruit and within the pedicel. Field trials revealed, that fruit shedding could be reduced by irrigation and plant growth regulator (PGR) application throughout the 3-year experiment study; however, it remains unclear how climatic conditons might induce hormonal response and thus enhance fruit shedding at different stages of fruit development. The present research project consists of three studies. First it was to determined which single or multiple climatic cues trigger fruit shedding in mango. Second, it was attempted to alleviate fruit abscission by PGR spray application at post-bloom and early developmental stages of the fruit in comparison with regular irrigation scheduling to reduce extensive fruit abscission. Third, the morphological changes in the abscission zone of mango pedicel during fruit abscission were studied. The timely changes of plant tissue IAA concentration and its key role in the abscission process was also evaluated. The research work was conducted in a commercial orchard near the township of Yen Chau in 2007, 2008 and 2009. The experimental design consisted of 20 randomly selected 10-year-old mango trees of each of the cultivars ?Hôi? and ?Tròn?. Half of the trees were irrigated at 3-day-intervals by mircospinkler and the remaining trees served as non-irrigated controls. For the PGR applications, 3 trees of each cultivar in 2008, and 6 trees of each cultivar in 2009 were used. In both experiments, 10 randomly selected inflorescences per tree were labelled and counted twice per until end of the fruit drop period. Fruit tissue was collected on-site from irrigated and non-irrigated trees. The fruit export of the endogenous indole-3-acetic acid was analyzed by Radio-Immuno-Assay (RIA). Further, to clarify the morphological changes within the abscission zone (AZ) of mango pedicels, samples of irrigated and control trees were collected, fixed and embedded, using a modified dehydration and embedding technique by vacuum infiltration. The results of the first part of this study indicate that the onset of the hot, dry prevailing winds induced the fruit drop. Whether fruit drop was reduced by irrigation seems to depend on the level of soil water deficiency, hence the reduction of plant water potentials. The results of the second part of the study showed that PGR applications reduced excessive fruit drop. Although all chemical treatments indicated significant effects, a single spray application of N-(2-chloro-4-pyridyl)-N-phenylurea (CPPU) and 1-naphtaleneacetic acid (NAA) effectively improved fruit retention. Furthermore, those spray applications led to a greater fruit set per inflorescennce than irrigation. However, IAA-export was not clearly affected by irrigation or PGR applications. The results of the third part of the study indicate positive effect of irrigation on fruit retention in both cultivars, which might be influenced by increased pedicel thickness thus increased carbon/nutrient availability to the fruit during critical environmental periods. Moreover, shortage of carboydrate supply to the fruit may be associated with a reduction of IAA-export out of the fruit and this in turn triggers the abscission process. In conclusion, this research proved that prevailing environmental conditons, particulary hot, dry winds, induce premature fruit drop in mango in Northern Vietnam. The identification of the physiological basis of premature fruit drop allowed the development of effective crop management strategies (e.g. PGR applications, irrigation) to overcome unfavourable environmental conditions and to reduce or even inhibit plant responses associated with premature fruit drop. The presented results suggest, that setting up an irrigation system increased fruit retention, which; however, is a great investment for farmers. It was shown that the ease of PGR application and the efficiency of the treatment is a promising alternative to irrigation in oder to prevent excessive fruit drop in mango. The development of effective, fruit drop reducing crop management strategies may also optimized crop loads and enhanced financial returns to growers.
Rice genotypic variation on phenological development and yield performance in cold prone high altitude cropping systems
(2021) Abera, Bayuh Belay; Asch, Folkard
Despite a huge potential for rice intensification, several constraints have been reported as bottlenecks for rice production in the East African high-altitude cropping system. In this system, yield reductions are mainly caused by moisture deficit, which dictates the sowing date of the crops, and cold stress, which can occur either during specific crop growth phases or during the entire cropping period. In order to minimize yield losses, cultivation of suitable genotypes and timely implementation of proved crop management options are implicitly needed. Therefore, the objectives of this study were to investigate the effects of weather during specific development stages on yield and yield components of a large number of rice genotypes contrasting in crop duration; to explore the effects of crop establishment method on the performance of a set of rice genotypes in high altitude; and to identify key data sets required for the adaptation of agricultural decision support tools to new environments: the case of RiceAdvice being introduced to the highlands of East Africa. Field trials were conducted during the cropping seasons of 2016 and 2017 at the Fogera rice research station in Ethiopia. Further, to generate data to be used for the advancement of RiceAdvice, trials were implemented in Madagascar (Ambohibary and Ivory) and Rwanda (Bugarama and Rwasave) at different altitudes. Thirty contrasting genotypes were included in the study to investigate the effects early and late sowing and the related weather variation experienced by the crop. The crop establishment methods (direct seeding and transplanting) were evaluated using nine contrasting genotypes. Daily mean, minimum, and maximum temperature, rainfall, radiation, and relative air humidity were recorded during the experimental period; and the phenological development of each genotype was closely monitored in all trials. Data on grain yield and yield components were recorded and finally subjected to analysis of variance. Results showed that yield was positively correlated with the percentage of filled spikelets and the number of productive tillers, and negatively correlated with the number of tillers per hill. Genotypes differed in duration, yield, and yield components between the two years, which was related to both, differences in sowing date as well as differences in weather conditions. Early sowing in 2017 led to an extended duration until maturity of short-duration genotypes, which was related to low radiation levels as the vegetative phase of short duration genotypes entirely took place during the cloudy rainy season. Contrastingly, the duration to maturity of medium- and long-duration genotypes was shortened after early sowing in 2017, probably related to higher relative air humidity. In 2016, late sowing in combination with the early onset of the cool period led to high spikelet sterility in medium- and long-duration genotypes, as the cold-sensitive booting phase took place during the cold spell. Therefore, effects of sowing date on yield differed between genotype groups with short-duration genotypes suffering and medium- and long-duration genotypes profiting from early sowing and vice versa for late sowing. Similar results were obtained in the experiment conducted in Madagascar and Rwanda. At high altitude in Madagascar, short-duration genotypes performed well after late sowing, whereas medium-duration genotypes performed better after sowing one to two months earlier. Also, in Rwanda, delayed sowing compromised yield because of spikelet sterility related to low-temperature during the reproductive stage. Therefore, it was concluded that the choice of variety should depend on the sowing date, which is dictated by the onset of rains. Further, decisions on management intervention have to consider season-specific constraints. Comparison of transplanted and direct seeded rice showed that, in general, transplanting had a strong advantage over direct seeding. While at high-altitudes, growing medium- and long-duration genotypes with a high yield potential bears the strong risk of yield loss due to cold sterility, transplanting, which resulted in significantly higher yields than direct seeding, can mitigate this risk. As after transplanting, physiological maturity was observed earlier in the season than after direct seeding, rice plants, including medium- and long-duration genotypes, escaped the low temperature stress at the critical reproductive stage, and thus, low spikelet fertility. Thus, with a relatively cold tolerant genotype such as Yun-Keng, sowing a few weeks earlier within an irrigated nursery can make use of the full potential and increase yields. Comparison of the experimental sites in Ethiopia, Madagascar and Rwanda, showed that the mean temperature between sowing and flowering of the four tested genotypes was negatively correlated with altitude. In general, precise knowledge of the duration of the potentially suitable genotypes is required and a crop model that is well-calibrated for the genotypes as well as for the environment, in combination with a smartphone application such as RiceAdvice, would be of great help to support farmers’ decision-making. The data recorded from the three countries field trials can be used as data source to validate RiceAdvice, and thus, increase its applicability.