Root microbial interactions to enhance wheat productivity under water stress
Date
2018
Authors
Salem, Galal Saleh Ali, author
Weir, Tiffany, advisor
Stromberger, Mary, committee member
Wallner, Stephen, committee member
Vivanco, Jorge, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Water stress is one of the obstacles that most profoundly affects plant growth and crop yields worldwide. Water stress causes serious plant growth problems such as suppression of cell growth and photosynthesis, disturbance of plant water relations, and increased production of the plant hormone ethylene, which reduces plant root and shoot length, consequently hampering the growth and productivity of crop plants. Wheat (Triticum aestivum L.) is one of the most important staple food crops, and is one of the most widely cultivated crops worldwide. Water deficit is the major limiting factor for wheat productivity, affecting yield and crop productivity. As a consequence, studying the water stress tolerance and productivity of wheat is extremely important to cope with the issue of food security in the face of a changing climate. Microbial inoculants that improve plant performance offer an environmentally friendly and sustainable strategy to cope with water deficit. Plant growth-promoting rhizobacteria (PGPR) are defined as a group of beneficial bacteria capable of colonizing the rhizosphere and contribute to increased plant growth and crop productivity via different direct and indirect mechanisms, such as production of plant growth regulators such as cytokinins, auxins, and gibberellins, inhibition of stress ethylene by ACC deaminase enzyme, or suppression of soil-borne pathogens by induction of plant defense mechanisms such as production of antibiotics or induced systemic resistance to cope with microbial pathogen attack. The purpose of this research was to assess the performance of 1-aminocyclopropane-1-carboxylate (ACC) deaminase- positive bacteria (ACC+ bacteria) inoculants isolated from Colorado soils on growth parameters and performance of different winter wheat genotypes grown in a greenhouse under water-stressed and well-watered conditions (Chapter 2). The results of this study showed that under water stress, leaf relative water content was improved among genotypes in response to inoculation, whereas the growth responses of winter wheat to inoculation with ACC+ bacteria depended on the wheat genotype tested. Understanding of the biological underpinnings of the relationships between different genotypes and PGPRs could be clarified by exploring the chemical signals that mediate these interactions. Therefore, in chapter 3, a global metabolomics analysis of rhizosphere-associated metabolites was conducted to identify chemical signals that may be important in these interactions. The prime objective of this chapter was to identify whether specific root metabolites were associated with improved resistance to water stress. Root exudates from three winter wheat genotypes, under well-watered or water-stressed conditions and with or without inoculation by ACC+ bacteria, were collected and analyzed for global metabolite profile differences. By using untargeted UPLC-MS/GC-MS models for studying root exudate profiles of winter wheat genotypes that differ in their ability to withstand water stress combined with multivariate statistical techniques (PCA and OPLS-DA), we were able to identify statistically and potentially significant biochemical compounds that may contribute to improvement the stress tolerance in specific winter wheat genotypes. The results revealed that metabolite profiles were most influenced by irrigation status, with global differences between water stressed and well-watered plants evident from both unsupervised (PCA) and supervised (OPLS-DA) ordination plots of the data. In particular, water stress plants had higher levels of the citric acid cycle intermediate, succinate, as well as organic acids such as lactic acid. These compounds have been shown to be produced by bacteria and to enhance plant growth under varying environmental stress conditions. The data also illustrate that metabolomic profiling is a powerful tool for generating specific hypotheses related to novel mechanisms of plant-microbe interactions for attenuation of water stress in winter wheat.