Abiotic stresses significantly reduce crop yield, causing serious problems in agriculture. Understanding the mechanisms of plant stress responses could contribute to the improvement of their stress tolerance. Phytohormones play an important role in plant stress defence as well as in regulation of growth and development. This thesis summarizes the results published in four articles focused on the evaluation of the effects of phytohormones during abiotic stresses, namely salinity, drought, ZnO nanoparticle treatment and cold stress. The main emphasis is put on abscisic acid as the key regulator of water status and stress defence, and on cytokinins, which regulate plant growth and stabilize photosynthetic machinery. Cytokinins act antagonistically to abscisic acid. Our results showed that abscisic acid is a general abiotic stress response regulator. Stress- tolerant plants (halophyte Thellungiella salsuginea or winter line of einkorn wheat Triticum monococcum) had a higher basal level of this hormone, especially in shoot meristematic tissues (apices, crowns), than stress-sensitive plants. Stress-tolerant plants reacted faster and in a more flexible way to stress. Active cytokinins were negatively affected by stress, which was associated with growth suppression. The drought stress study showed that...

<p>  </p> <p>Modern agriculture must address the massive challenge of providing food for the increasing population. The challenge lies in increasing crop yield and reducing losses caused by abiotic and biotic stresses. In fact, for some crops, such as wheat and maize, over 40% of the production is lost due to environmental conditions (abiotic stresses) or pests and pathogens (biotic stresses). Specialists in the area are suggesting a need for a second green revolution to meet the increasing demand in food production. While in the first green revolution was focused on breeding and genetics to produce crops' genetic lines with a higher yield. The second green revolution will utilize cutting-edge technologies to increase yield and reduce crop losses. The development of remote sensing technologies and their applications is the main driving force of modern agricultural practices. Currently, farmers are relying more on automation, data collection, and data analysis to manage farming operations. The reliance on remote sensor technologies is a game-changer for traditional agricultural practices, and it is contributing tremendously to increasing production and avoiding yield losses. Hyperspectral phenotyping is an emerging remote sensing technology that utilizes the light's reflectance to provide insightful information about plant traits. For several years, research groups have been applying hyperspectral phenotyping techniques to detect plant traits information, such as nitrogen content, photosynthesis rates, pests infestation, and abiotic stress detection. Although this is not a novel approach to plant traits detection, this technology application is not mature yet. Several challenges are associated with using hyperspectral information for phenotyping, such as model transferability, data collection scalability, and the heritability of plant traits retrieved using hyperspectral data. In my thesis dissertation, I addressed some of those challenges contributing to advances in hyperspectral phenotyping. My results demonstrate that using full-range hyperspectral reflectance data (400-2400nm) to retrieve nitrogen in winter wheat increases the model transferability across years and genotypes. Predicting nitrogen content using hyperspectral data can be used as a surrogate to calculate nitrogen use efficiency traits. My research highlights the hurdles associated with spectral detection of stresses interaction, such as drought stress, which can mask western corn rootworm detection in maize. Finally, I explored the correlation among spectral, functional, and field traits in a soybean NAM (Nested Association Mapping) population to understand the relationship among those traits' variability and how that information can be used for soybean breeding programs. The outcomes of my thesis dissertation advance the knowledge in the hyperspectral phenotyping field and its application to modern agriculture. Consequently, my study also contributes to food security programs by providing insightful information about the hyperspectral assessment of plant health status, which is essential to increase yield production and reduce crop losses. </p>

Biotic and abiotic stresses are signifi cant factors limiting the production of food and other supporting materials required to sustain increasing world population. Plant health is directly related to human health and is increasingly becoming signifi cant and demands more attention towards limiting the damages caused by biotic and abiotic stresses. Signifi cant progress has been made towards our understanding of the processes, which mediate both biotic and abiotic stress signaling in plants. Signifi cant role is played by various plant hormones, e.g., salicylic acid (SA) and jasmonic acid (JA) in biotic stress and abscisic acid (ABA) in abiotic stress (Annu Rev Cell Dev Biol 28:489-521, 2012). Other hormones with minor role include the cytokinins (CK), auxins (indole 3 acetic acid. IAA), and the brassinosteroids (BR) (Annu Rev Cell Dev Biol 28:489-521, 2012). Cross talk between these plant hormones is signifi cant and may result in either synergistic or antagonistic effect on stress responses (Annu Rev Cell Dev Biol 28:489-521, 2012). In recent years, extensive research carried out in various laboratories has implicated cross talk between the ABA and the SA in abiotic stress response. This is signifi cant in light of SA being key player in biotic stress responses in plants. This review will discuss the role of SA in biotic and abiotic stress signaling and its cross talk with other hormones in mediating abiotic stress signaling in plants.

Georeferenced field data were used to develop logistic regression models of the geographic distribution of 38 frequently common plant species throughout Rich County, Utah, to assist in the future correlation of Natural Resources Conservation Service Ecological Site Descriptions to soil map units. Field data were collected primarily during the summer of 2007, and augmented with previously existing data collected in 2001 and 2006. Several abiotic parameters and Landsat Thematic Mapper imagery were used to stratify the study area into sampling units prior to the 2007 field season. Models were initially evaluated using an independent dataset extracted from data collected by the Bureau of Land Management and by another research project conducted in Rich County by Utah State University. By using this independent dataset, model accuracy statistics widely varied across individual species, but the average model sensitivity (modeling a species as common where it was common in the independent dataset) was 0.626, and the average overall correct classification rate was 0.683. Because of concerns pertaining to the appropriateness of the independent dataset for evaluation, models were also evaluated using an internal cross-validation procedure. Model accuracy statistics computed by this procedure averaged 0.734 for sensitivity and 0.813 for overall correct classification rate. There was less variability in accuracy statistics across species using the internal cross-validation procedure. Despite concerns with the independent dataset, we wanted to determine if models would be improved, based on internal cross-validation accuracy statistics, by adding these data to the original training data. Results indicated that the original training data, collected with this modeling effort in mind, were better for choosing model parameters, but sometimes model coefficients were better when computed using the combined dataset.

Doctor Educationis / Maize (Zea mays L.) is grown globally as an important grain crop in South Africa, United States, China and Brazil and plays a major role in the worldwide economy. In South Africa, the grain is utilised for food consumption, livestock feed, for malting purposes and bioethanol production. Maize contains approximately 72% starch, 10% protein, 4% fat and supplying an energy density of 365 Kcal/100 g. The production of grain crops in South Africa is restricted by various factors such as abiotic and biotic stresses. The fungal genus Aspergillus is one of the most important biotic stresses affecting maize in the country. Aspergillus flavus can contaminate a wide range of agricultural commodities either in storage or field. Hydrogen sulfide appears to have a potential in the mechanism of resistance against pathogen attack by Aspergillus flavus. / 2023

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The occurrence of phenotypic and genotypic diversity is the key factor in crop improvement including abiotic stress tolerance. The focal objectives of this study were to evaluate and characterize 74 tropical indica rice breeding lines for phenotypic and genotypic diversity, screening for the most devastating abiotic stresses in rice; drought and salinity at the seedling stage at morpho-physiological and molecular levels. To fulfill these objectives, five studies were conducted in pots; first two experiments aimed at assessing phenotypic and yield variability at seedling and maturity stages respectively; based on several (more than 20) root and shoot traits which exploited a wide range of variability among genotypes for measured traits. Germplasm was then screened for drought stress at two moister regimes, 50%, and 100% moisture levels, under mini-hoop structures. Nine percent of the genotypes exhibited a high tolerance to drought stress, and genotypes IR86638 and IR49830 were identified as the most and least drought tolerant respectively. Germplasm was also screened for salinity tolerance in pure sand pot-culture (a simple, efficient and alternate screening method) at three levels; high salt stress (EC 12 dSm-1), moderate salt stress (EC 6 dSm-1), and control imposed one week after emergence. Thirteen genotypes (17.57%) were identified as highly salt tolerant; genotypes FED 473 and IR85427 were highly salt tolerant and salt sensitive, respectively. Root traits were found more crucial and best descriptors in identifying both salinity and drought tolerant genotypes. Genotypes were further used in Genome-wide Association Study (GWAS) to uncover important SNPs, QTLs or genes related to salinity tolerance. A higher number of significant SNPs were discovered for root traits, indicting the importance of root traits in identifying abiotic stress tolerance in rice. The knowledge gained from this investigation could be useful in breeding for better crop establishment, yield improvement, screening for any abiotic stress tolerance.

Abiotic stresses such as drought, salt and exposure to toxic metals adversely affect the growth and productivity of crop plants and are serious threats to agriculture. We are currently working with an Arabidopsis family of proteins known as Stress Associated Proteins (SAPs). There are a total of 14 proteins in the Arabidopsis SAP family whose members have been suggested to provide tolerance to abiotic stresses in plants. For this project, we aim to characterize AtSAP13, which codes for a protein of 249 amino acid residues. Through overexpression, we investigated the sensitivity or tolerances provided by the overexpressed protein in comparison to wild-type plants. Our preliminary results showed that Arabidopsis plants overexpressing SAP13 showed strong tolerance to arsenite, cadmium, and zinc. A semi-quantitative RT-PCR was performed to analyze SAP13’s mRNA levels in wild type plants exposed to the same set of stresses. Tissue specific expression was analyzed using a GUS histochemical assay. Sub-cellular localization of AtSAP13 was analyzed by creating an in-frame fusion of SAP13 and enhanced GFP (eGFP). We set out to optimize growth conditions for Crambe abyssinica in order to determine if Crambe could be grown as a biofuel crop in New England. We have determined that Crambe can be grown successfully in the New England climate. We tested three fertilizer application rates, two different cultivars, and two different soil types for changes in yield. In the end, we observed the greatest increase in yield when planted on well drained soil.

Lettuce is a highly nutritional crop that is sensitive to multiple stresses, including salt stress. The decreasing availability of salt-free water is posing a major challenge to growing nutritious lettuce in hydroponic systems. Despite evidence that salt stress affects yield and nutrition, its impacts on economically important growth stages are overlooked. This study addressed the knowledge gaps regarding the salt stress impact on romaine lettuce. Four independent experiments were conducted in controlled environment conditions using 2-38 lettuce genotypes, to assess the effects of salt stress at rosette or head formation. An increase in sodium chloride (NaCl) levels (0 to 150 mM) linearly decreased lettuce biomass. A positive association was observed between NaCl and sodium to potassium ion ratio. Lettuce was found to be sensitive to salt above 40 mM NaCl. The phenotyping of 38 lettuce genotypes revealed significant variability in salt stress tolerance. Genotype, Green forest exhibited a higher decline in fresh and dry biomass compared to Burgundy delight, indicating its higher sensitivity to salt stress. Sodium accumulation was significantly higher in both genotypes under salt stress, while potassium decreased in Green forest but remained relatively stable in Burgundy Delight. Hydro-primed lettuce had higher photosynthetic efficiency and oxidative stress tolerance than the control. Hydro-priming seed treatment could be used as a cost-effective priming technique to boost economic efficiency under stress. In addition, the low sodium: potassium ratio and high biomass can be used as indicators for selecting salt-tolerant genotypes.

The Effect of Abiotic Elicitors on the Content of Secondary Metabolites in In vitro Plant Cultures - II. The method of elicitation is used for the increased production of secondary metabolites in in vitro plant cultures. In this study, there the effect of pyridine derivate N-(5-chlorpyridin-2-yl)-4-ethylbenzamide in three concentration - 3.845.10-3 mol/l; 3.845.10-4 mol/l and 3.845.10-5 mol/l for the production of flavonolignans in callus and suspension cultures of Silybum marianum was tested. The evaluation of elicitation effect proceeded after 6, 24, 48, 72 a 168 hours against control samples without the elicitor treatment after 24 and 168 hours. In the same intervals the samples of culture medium were taken and assessed. The cells were cultivated on Murashige and Skoog medium with 10 mg/ml of α-naphtylacetic acid as growth regulator. The obtained and adjusted samples were analysed by the HPLC method. From the parts of silymarin complex were detected silychristin, silybin A, isosylibin A, isosilybin B. Flavonoid taxifolin wasn̕ t detected in any case. In callus culture, there was achieved a maximal production of all detected components of silymarin complex (30.508 μg/g DW) after 168 hours of elicitor treatment in concentration of 3.845.10-4 mol/l, it was about only substance - silychristin. The...