Thirty-two isolates of rhizosphere bacteria, selected for their ability to inhibit zoospore germination and/or mycelial growth of Pythium aphanidermatum (Pa) in vitro, were evaluated in a test tube bioassay using cucumber c.v. 'Straight 8'. These isolates were identified as Psedudomonas corrugata (Pc13 or 35) and P. fluorescens (Pf15, 16 or 27). All but one of the five isolates effectively colonised the roots of cucumber plants in short term studies. Isolates 15 and 35 were found to maintain high population densities throughout the time period. Pa-inoculated plants treated with the Pc13 or Pf15 produced fruit yields equal to 92 and 74% respectively of the control (no Pa, no bacteria). Pa-inoculated plants without bacteria yielded only 46% of the control. In the fall crop, Pa-inoculated plants treated with Pc13 or Pf15 yielded 52 and 47% of the control compared to Pa-only treatment, which yielded 12.5% of the control. In both crops, treatment with any of the bacterial isolates resulted in significantly reduced cull rates compared to the Pa-only treatment.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Plant growth promoting substances (PGPS) are emerging as useful tools in the investigation of important plant growth traits. Two PGPS, smoke-water derived from burning plant material and a synthetic strigolactone analogue, GR24, have been reported to regulate a wide variety of developmental and growth processes in plants. These PGPS are beginning to receive considerable attention in the area of improving plant biomass yield and production. Variation in growth between plants is a major impediment towards the complete understanding of the intrinsic processes that control biomass production. Callus cultures of the model plant Arabidopsis thaliana could overcome some of these hindrances. However, the suitability of these callus cultures as a model system for plant biomass production must be established first. This study aimed at using A. thaliana callus cultures as a platform to study the plant growth promoting activities of smoke-water and GR24. The first part of this study was conducted to develop an optimal protocol for inducing A. thaliana callus formation. Wild-type A. thaliana Col-O, as well as strigolactone deficient and insensitive mutants (max1-1, max2-1, max2-2, max3-9 and max4-1) were cultured for callus induction. Hypocotyl and leaf explants were cultured onto MS media supplemented with different hormone concentrations of 2,4-D and kinetin (2:2 mg/L 2,4-D:kinetin and 0.5:0.05 mg/L 2,4-D:kinetin). Both media proved suitable for callus induction of all genotypes, with max1-1 showing the highest efficiency (83.33% and 92.22%) of callus induction. Calli were then used as a platform for future investigations into the effects of smoke-water and GR24. Secondly, this study examined the effects of smoke-water and GR24 on wild-type A. thaliana Col-O callus. Basic physiological studies were conducted to determine if these two compounds would positively affect callus growth, as was shown in previous studies using whole plants. Calli cultivated on MS media containing the two different hormone concentrations were transferred onto the same fresh MS medium, supplemented with either smoke-water or GR24. Growth promotion by smoke-water and GR24 in calli was characterized by a significantly increased mass (biomass). Calli were additionally transferred onto MS medium containing either auxin only or kinetin only and supplemented with GR24 or smoke-water. In the auxin only system, increased mass was recorded for both GR24 and smoke-water treatments, while these two compounds seemed to reduce growth in the kinetin only system. The positive growth stimulatory effect observed for the auxin only system could be attributed to the synergistic relationship between auxin and strigolactones, whilst the reduced mass in the latter system could be due to the antagonistic interaction between strigolactones and cytokinins. Finally, this study has discovered a dual role of strigolactones in biomass accumulation and adventitious root formation for Arabidopsis thaliana callus. On an auxin- and cytokinin-free MS medium supplemented with GR24, calli of Arabidopsis thaliana strigolactone deficient mutants (max1-1 and max4-1) and the wild-type Col- O, but not the strigolactone response mutant (max2-2), showed enhanced biomass accumulation. In addition to this, the max4-1 mutant and wild-type Col-O demonstrated enhanced adventitious rooting, which was not apparent in max2-2. Together these data suggested that the biomass accumulation and the adventitious rooting activities of GR24 in Arabidopsis thaliana calli are controlled in a MAX2- dependent manner. The interaction between strigolactone, auxin and cytokinin signalling pathways in regulating these responses appears to be complex. Gene expression profiling showed regulation of stress-related genes such as B-box transcription factors, CALCINEURIN B-LIKE and RAP4.2 Genes encoding hormones associated with stress (ABA, ethylene) and defence mechanisms (JA) were upregulated. Expression of stress related genes indicated clues on some kind of stress mediation that might be involved during the regulation of the rhizogenic response. Conversely, smoke-water treatment could not enhance the biomass of the calli and nor could it induce adventitious rooting in the absence of auxin and cytokinin. This observation strongly emphasized the distinct roles of these two compounds, as well as the importance of the interaction and ratio of auxin and cytokinin in callus growth. This study has demonstrated a novel role of strigolactones in plant growth and development, i.e. enhancement of biomass production in callus cultures. Secondly the enhanced adventitious rooting ability is in agreement with recently published literature on the role of strigolactones in regulating root architecture. In vitro callus production is advantageous to plant sciences. It creates an opportunity for increasing plant material for cultivation and offers the use of cell cultures that accurately mimic specific growth responses. It could greatly contribute to the study of intricate regulatory and signalling pathways responsible for growth and development in plants. Because the regulation of plant biomass production is very complex and the molecular mechanisms underlying the process remain elusive, it is of paramount importance that further work be done in order to gain more in-depth insights and understanding of this aspect and subsequently improve efficiency and returns when applying biotechnology tools on commercially important crop plants. / AFRIKAANSE OPSOMMING: Verbindings wat plantgroei bevorder (PGBV) het as nuttige alternatief ontstaan om plant groei te ondersoek. Rook-water, afkomstig van verbrande plant material, en ‘n sintetiese strigolaktoon analoog, GR24, wat ‘n α, β-onversadigde furanoon funksionele groep in gemeen het, is vir die regulering van ‘n wye verskeidenheid ontwikkelings- en groei prosesse in plante verantwoordelik. Tans ontvang hierdie PGBVs aansienlik aandag in die area van die verbetering van plant biomassa opbrengs en -produksie. Die variasie in groei tussen plante is ‘n groot hindernis om die intrinsieke prosesse wat biomass produksie beheer, volledige te verstaan. Deur gebruik te maak van kallus kulture van die model plant Arabidopsis thaliana kan van hierdie hindernisse oorkom word. Tog moet die geskiktheid van kallus kulture as ‘n model sisteem vir plant groei biomass produksie eers gevestig word. Die doel van hierdie studie was om A. thaliana kallus kulture as ‘n platform vir die studie van die plantgroei bevorderingsaktiwiteite van rook-water en GR24 te gebruik. Die eerste deel van die studie is uitgevoer ten einde ‘n optimale protokol vir die induksie van A. thaliana kallus produksie te ontwikkel. Wilde tipe Col-0, asook strigolaktoon afwesige en onsensitiewe mutante (max1-1, max2-1, max2-2, max3-9 en max4-1) is vir kallus induksie gekultiveer. Hipokotiel en blaar eksplante is op MS medium wat verskillende hormoon konsentrasies van 2,4-D en kinetien (2:2 mg/L 2,4-D:kinetien en 0.5:0.05 mg/L 2,4-D:kinetien) bevat, oorgedra. Beide media was geskik vir kallus induksie van al die genotipes, met max1-1 wat die hoogste effektiwiteit (83.33% en 92.22%) van kallus induksie getoon het. Kalli is daarna as ‘n platform vir toekomstige navorsing i.v.m die effek van rook-water en GR24 gebruik. Tweedens ondersoek die studie die effek van rook-water en GR24 op wilde tipe Col-0 kallus. Basiese fisiologiese studies is uitgevoer om te bepaal of die twee verbindings ‘n positiewe effek op kallus groei toon soos aangedui in vorige studies waar intakte plante gebruik is. Kallus wat op MS medium wat die twee verskillende hormoon konsentrasies bevat gekultiveer was, is op dieselfde vars MS medium, wat addisioneel óf rook-water óf GR24 bevat, oorgedra. Die stimulering van groei van kalli deur rook-water en GR24 is deur ‘n merkwaardige toename in massa (biomassa) gekenmerk. Kallus is additioneel op MS medium wat slegs óf ouksien óf kinetin bevat (gekombineer met GR24 of rook-water behandeling), oorgedra. In die sisteem waar slegs ouksien toegedien is, is ‘n toename in massa waargeneem vir beide GR24 en rook-water behandelinge. In teenstelling hiermee, het die twee verbindings in die sisteem waar slegs kinetin toegedien is, ‘n vermindering in groei meegebring. Die positiewe groei stimulerende effek wat waargeneem is vir die sisteem waar slegs ouksien toegedien is, kan toegedra word aan die sinergistiese verhouding tussen die ouksien en strigolaktone; terwyl die verlaagde massa in die laasgenoemde sisteem aan die antagonistiese interaksie tussen strigolaktone en sitokiniene toegedra kan word. Laastens het hierdie studie het ‘n gelyktydige rol van strigolaktone vir biomassa akkumulasie en bywortelvorming in Arabidopsis thaliana kallus ontdek. Kallus van A. thaliana strigolaktoon afwesige mutante (max1-1 en max4-1) en die wilde tipe Col-0 (maar nie die strigolaktoon reagerende mutant (max2-2) het op ‘n ouksien en sitokinien vrye MS medium wat GR24 bevat ‘n verhoogde biomassa akkumulasie getoon. Die max4-1 mutant en wilde tipe Col-0 het verhoogde bywortelvorming getoon, wat nie so opmerklik by max2-2 was nie. Hierdie data het tesame voorgestel dat die biomassa akkumulasie en die bywortelvormingsaktiwiteite van GR24 in Arabidopsis thaliana kallus op ‘n MAX2-afhanklike wyse beheer word. Die interaksie tussen strigolaktoon, ouksien en sitokinien sein transduksie paaie vir die regulering van hierdie reaksies blyk kompleks te wees. Die geen uitdrukkingsprofiel het die regulering van stres verwante gene soos B-boks transkripsie faktore, CALCINEURIN B-LIKE en RAP4.2, getoon. Gene wat vir hormone wat aan stres (ABA, etileen) en verdedigingsmeganismes (JA) verwant is, is opgereguleer. Die uitdrukking van stress verwante gene dui op tekens van ‘n ander tipe stres bemiddeling wat dalk by die regulering van die risogeniese reaksie betrokke kan wees. In teenstelling, rook water behandeling kon nie die kallus biomassa verhoog nie en dit kon ook nie die bywortelingvorming in die afwesigheid van ouksien en sitokiniene induseer nie. Hierdie waarneming is ‘n sterk bevestiging vir die uitsonderlike rol van die twee verbindings, asook die belang van die interaksie en verhouding van ouksien en sitokinine vir die groei van kallus. Hierdie studie toon op ‘n nuwe rol van strigolaktoon in plant groei en ontwikkeling, d.w.s die verhoogde biomassa produksie in kallus kulture. Tweedens, die verhoogde bywortelvormingsvermoë is in ooreenstemming met literatuur wat onlangs gepubliseer is i.v.m die rol van strigolaktone in die regulering van wortel argitektuur. Die in vitro produksie van kallus is voordelig in plant wetenskappe. Dit skep ‘n geleentheid vir die vermeerdering van plant materiaal vir kultivering en bied die gebruik van selkulture wat spesifieke groei reaksies op ‘n merkwaardige wyse akkuraat namaak. Dit kan grootliks bydra tot die studie van die delikate regulatoriese en sein transduksie paaie wat vir groei en ontwikkeling van plante verantwoordelik is. Aangesien die regulering van plant biomassa produksie baie kompleks is en die molekulêre meganismes vir die proses onbekend bly is dit van grootskaalse belang dat meer werk gedoen word om ‘n meer in diepte insig en kennis van die aspekte en gevolglike verbetering van effektiwiteit en wins te kry deur die toepassing van biotegnologiese metodes op die gewas plante wat van kommersiêle belang is.

Plant roots are central to C- and N-cycling in soil. However, (i) plants differ strongly in tissue recalcitrance (e.g. lignin content) affecting their mineralization in soil, and (ii) rhizodeposits also vary strongly in terms of the metabolites that they contain. Therefore, (i) we used 13C labelled ryegrass root and shoot residues as substrates to investigate the impact of tissue recalcitrance on soil processes through controlled incubation of soil, (ii) we assessed variations in root C-deposition between barley genotypes and their respective impacts on soil processes using 13CO2 labelled plants, (iii) using 13C/15N enriched ryegrass root residues as tracer material, we investigated the impacts of barley genotypes on mineralization of recently incorporated plant residues in soil and plant uptake of the residue-derived N, and (iv) we applied a quantitative trait loci analysis approach to identify barley chromosome regions affecting soil microbial biomass and other soil and root related traits. In the first study, addition of root residues resulted in reduced C-mineralization rates, soil microbial activity and soil organic matter (SOM) priming relative to shoot residues. Planted experiments revealed (i) genotype effects on plant-, SOM- and residuederived surface soil CO2-C efflux and showed that incorporation of plant derived-C to the silt-and-clay soil fraction varied between genotypes, indicating relative stabilization of root derived-C as a result of barley genotype, (ii) that plant uptake of residue released N between genotypes was linked to genotype impacts on residue mineralization, and (iii) barley chromosome regions that influence plant-derived microbial biomass C. These results (i) suggest that greater plant tissue recalcitrance can lower soil C-emissions and increase C-storage in soil, and (ii) demonstrate the barley genetic influence on soil microbial communities and C- and N-cycling, which could be useful in crop breeding to improve soil microbial interactions, and thus promote sustainable crop production systems.

Submitted by JULIANA SILVA RODRIGUES CABRAL null (jsrcabral@gmail.com) on 2016-08-30T23:49:11Z No. of bitstreams: 1 TESE - JULIANA SILVA RODRIGUES CABRAL.pdf: 1613065 bytes, checksum: 9d267faa19bdb0318205440f3bd75671 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-08-31T18:43:17Z (GMT) No. of bitstreams: 1 cabral_jsr_dr_ilha.pdf: 1613065 bytes, checksum: 9d267faa19bdb0318205440f3bd75671 (MD5) / Made available in DSpace on 2016-08-31T18:43:17Z (GMT). No. of bitstreams: 1 cabral_jsr_dr_ilha.pdf: 1613065 bytes, checksum: 9d267faa19bdb0318205440f3bd75671 (MD5) Previous issue date: 2016-07-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A mangabeira (Hancornia speciosa Gomes) se destaca entre as árvores frutíferas nativas do cerrado como uma das mais promissoras para programas de exploração sustentável. Apesar do potencial econômico, a falta de informações sobre esta cultura vem restringindo seu cultivo comercial. A propagação sexuada desta espécie é dificultada, pois suas sementes têm curta longevidade e a redução do teor de água prejudica sua viabilidade e vigor. A técnica de micropropagação possibilita a multiplicação em massa de mudas com características geneticamente superiores, uniformes, em espaço físico reduzido e curto período de tempo. Entretanto, ela elimina os microrganismos associados ao tecido vegetal, incluindo mutualistas como os fungos micorrízicos arbusculares (FMA), além dos promotores de crescimento vegetal, que podem melhorar o desempenho da planta sob condições de estresse, além de aumentar o rendimento. A inoculação destes microrganismos durante a micropropagação tem sido recomendada para reduzir o tempo de formação das mudas e de aclimatização, aumentar a tolerância a estresses bióticos e abióticos, resistência a patógenos e porcentagem de sobrevivência das mudas após o transplante. Objetivou-se com este trabalho a aclimatização de plantas micropropagadas de mangabeira com diferentes substratos e câmara úmida, inoculadas com fungos promotores do crescimento vegetal (FPCV) in vitro e ex vitro, associados com o FMA Glomus clarum, em casa de vegetação, para maximizar a produção de mudas a serem utilizadas em programas de formação de pomares e reflorestamento. Os experimentos foram conduzidos na UNESP - Universidade Estadual Paulista, Campus de Ilha Solteira e Instituto Federal Goiano – Campus Rio Verde (IF Goiano – Campus Rio Verde). O material vegetal utilizado na propagação in vitro foi retirado de frutos de diferentes plantas de mangabeira coletados na Fazenda de Ensino, Pesquisa e Extensão da UNESP Campus Ilha Solteira e na Fazenda Gameleira, município de Montes Claros de Goiás - GO. Todos os experimentos foram realizados e conduzidos por 120 dias. A associação do saco plástico como câmara úmida com o substrato Bioplant®, seguido da pulverização de FPCV e inoculação do G. clarum é o método mais adequado para aclimatização de plantas micropropagadas de mangabeira, em casa de vegetação. / Mangabeira (Hancornia speciosa Gomes) stands out among the native fruit trees of the Cerrado as one of the most promising for sustainable exploitation programs. Despite the economic potential, lack of information about this culture is limiting its commercial cultivation. The sexual propagation of this species is difficult as its seeds have a short longevity, and reduced water content impairs their viability and vigor. The micropropagation technique enables the mass multiplication of plants with genetically superior features, uniform, in a reduced physical space and a short length of time. However, it eliminates the microorganisms associated with plant tissue, including mutualistcs, as mycorrhizal fungi (AMF), in addition to plant growth promoters, which can improve plant performance under stress conditions, and increase the yield. Inoculation of these microorganisms during micropropagation has been recommended to reduce the time of seedlings formation and acclimatization, and to increase tolerance to biotic and abiotic stresses, resistance to pathogens and percentage of seedling survival after transplantation. This study aimed the acclimatization of micropropagated plants with different substrates and moister chamber, inoculated with plant growth-promoting fungi (PGPF) vitro and ex vitro, associated with AMF Glomus clarum, in a greenhouse, to maximize seedlings production to be used in the mangabeira and reforestation programs. Experiments were conducted at UNESP- Universidade Estadual Paulista, Ilha Solteira Campus, and Federal Institute Goiano - Rio Verde Campus (IF Goiano - Campus Rio Verde). The plant material used in the in vitro propagation was removed from fruits of different mangabeira plants collected in Teaching, Research and Extension Farm of the UNESP Ilha Solteira Campus and Gameleira Farm, Montes Claros de Goiás-GO. All experiments were performed and conducted for 120 days. The association of plastic bag as a moist chamber with Bioplant® substrate, followed by spray PGPF and inoculation of G. clarum is the most appropriate method for acclimatization of micropropagated plants mangabeira in the greenhouse. The association of plastic bag as moist chamber with Bioplant® substrate, followed by spray PGPF and inoculation of G. clarum is the most appropriate method for acclimatization of micropropagated of mangabeira plants in the greenhouse. / FAPESP: 2012/14489-9

Orientador: Ana Maria Rodrigues Cassiolato / Resumo: A mangabeira (Hancornia speciosa Gomes) se destaca entre as árvores frutíferas nativas do cerrado como uma das mais promissoras para programas de exploração sustentável. Apesar do potencial econômico, a falta de informações sobre esta cultura vem restringindo seu cultivo comercial. A propagação sexuada desta espécie é dificultada, pois suas sementes têm curta longevidade e a redução do teor de água prejudica sua viabilidade e vigor. A técnica de micropropagação possibilita a multiplicação em massa de mudas com características geneticamente superiores, uniformes, em espaço físico reduzido e curto período de tempo. Entretanto, ela elimina os microrganismos associados ao tecido vegetal, incluindo mutualistas como os fungos micorrízicos arbusculares (FMA), além dos promotores de crescimento vegetal, que podem melhorar o desempenho da planta sob condições de estresse, além de aumentar o rendimento. A inoculação destes microrganismos durante a micropropagação tem sido recomendada para reduzir o tempo de formação das mudas e de aclimatização, aumentar a tolerância a estresses bióticos e abióticos, resistência a patógenos e porcentagem de sobrevivência das mudas após o transplante. Objetivou-se com este trabalho a aclimatização de plantas micropropagadas de mangabeira com diferentes substratos e câmara úmida, inoculadas com fungos promotores do crescimento vegetal (FPCV) in vitro e ex vitro, associados com o FMA Glomus clarum, em casa de vegetação, para maximizar a produção de mudas ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Mangabeira (Hancornia speciosa Gomes) stands out among the native fruit trees of the Cerrado as one of the most promising for sustainable exploitation programs. Despite the economic potential, lack of information about this culture is limiting its commercial cultivation. The sexual propagation of this species is difficult as its seeds have a short longevity, and reduced water content impairs their viability and vigor. The micropropagation technique enables the mass multiplication of plants with genetically superior features, uniform, in a reduced physical space and a short length of time. However, it eliminates the microorganisms associated with plant tissue, including mutualistcs, as mycorrhizal fungi (AMF), in addition to plant growth promoters, which can improve plant performance under stress conditions, and increase the yield. Inoculation of these microorganisms during micropropagation has been recommended to reduce the time of seedlings formation and acclimatization, and to increase tolerance to biotic and abiotic stresses, resistance to pathogens and percentage of seedling survival after transplantation. This study aimed the acclimatization of micropropagated plants with different substrates and moister chamber, inoculated with plant growth-promoting fungi (PGPF) vitro and ex vitro, associated with AMF Glomus clarum, in a greenhouse, to maximize seedlings production to be used in the mangabeira and reforestation programs. Experiments were conducted at UNESP- Universidad... (Complete abstract click electronic access below) / Doutor

Salt stress is a severe environmental challenge in agriculture, limiting the quality and productivity of the crops around the globe. Plant growth promoting rhizobacteria (PGPR) is proposed as a friendly solution to overcome those challenges. The desert plant endophytic bacterium, Enterobacter sp. SA187 has shown plant growth promotion and salt stress tolerance beneficial effect on the model plant Arabidopsis thaliana in vitro as well as under the field conditions on different crops. SA187 has a distinguished morphology of yellow colonies (SA187Y) that could be due to carotenoid biosynthesis. However, the bacteria tend to lose the yellow color upon incubation with the plants and the colonies turn to white (SA187W). In comparison to SA187Y, SA187W shows 50% reduction on the beneficial impact on A. thaliana fresh and dry weight of root and shoot system. By counting the CFU/plant, we showed that SA187Y and SA187W both have similar colonization rate in both shoots and roots. Under non-salt conditions, optimal bacterial colonization was observed on day 8 after inocubation, however, under the salt stress condition, the optimal colonization was observed at day 4. Moreover, during the time period of the incubation of the SA187Y with the plants, there was a consistent noticeable loss of the yellow color of the colonies. This change in color is only observed eight days after transfer and the number of white colonies increases with the increase of the incubation time. In addition, SA187W was GFP-tagged by Tn7 transposon system and visualized by confocal laser scanning microscopy. The SA187W-GFP colonies have shown a similar colonization pattern as SA187Y-GFP, bacteria were colonizing the differentiation zone and cell elongation zone in the roots. Finally, the gene expression of the carotenoid biosynthesis pathways genes in SA187Y showed an overall higher gene expression compared to SA187W. In conclusion, the color loss seems to affect the beneficial impact of the bacteria on plants. However, the reduced beneficial impact is not due to the colonization efficiency of bacteria on the plant roots but could be due to a regulation of gene expression of carotenoid biosynthesis.

One of the major challenges for agricultural research in the 21st century is to increase crop productivity to meet the growing demand for food and feed. Biotic (e.g. plant pathogens) and abiotic stresses (e.g. soil salinity) have detrimental effects on agricultural productivity, with yield losses being as high as 60% for major crops such as barley, corn, potatoes, sorghum, soybean and wheat, especially in semi-arid regions such as Saudi Arabia. Plant growth promoting bacteria isolated from pioneer desert plants could serve as an eco-friendly, sustainable solution for improving plant growth, stress tolerance and health. In this dissertation, culture-independent amplicon sequencing of bacterial communities revealed how native desert plants influence their surrounding bacterial communities in a phylogeny-dependent manner. By culture-dependent isolation of the plant endosphere compartments and a number of bioassays, more than a hundred bacterial isolates with various biochemical properties, such as nutrient acquisition, hormone production and growth under stress conditions were obtained. From this collection, five phylogenetically diverse bacterial strains were able to promote the growth of the model plant Arabidopsis thaliana under salinity stress conditions in a common mechanism of inducing transcriptional changes of tissue-specific ion transporters and lowering Na+/K+ ratios in the shoots. By combining a number of in vitro bioassays, plant phenotyping and volatile-mediated inhibition assays with next-generation sequencing technology, gas chromatography–mass spectrometry and bioinformatics tools, a candidate strain was presented as a multi-stress tolerance promoting bacterium with potential use in agriculture. Since recent research showed the importance of microbial partners for enhancing the growth and health of plants, a review of the different factors influencing plant-associated microbial communities is presented and a framework for the successful application of microbial inoculants in agriculture is proposed. The presented work demonstrates a holistic approach for tackling agricultural challenges using microbial inoculants from desert plants by combining culturomics, phenomics, genomics and transcriptomics. Microbial inoculants are promising tools for studying abiotic stress tolerance mechanisms in plants, and they provide an eco-friendly solution for increasing crop yield in arid and semi-arid regions, especially in light of a dramatically growing human population and detrimental effects of global warming and climate change.

Microorganisms will play a significant role in the agricultural revolution in the coming decades and help meet the growing population's needs. Hence, understanding the impact of beneficial bacteria on crop development is key to the future of developing microbial products. The ability of PGPB to increase crop yields has been recently investigated in agriculture, as PGPB can support and protect plants under different stresses. Since PGPB interactions occur naturally, finding a method to apply beneficial bacteria while maintaining their efficiency and quality is a topic of interest. PGPB have been used as microbial inoculants, biofertilizers, and also as seed coatings. Preservation of microorganisms through desiccation has been used as the preferred method for long-term storage of microbial culture. The use of dry powders is favored over liquid cultures due to their ease of transportation and better quality control. For microbial preservation, freeze-drying has been defined as the most convenient and satisfactory preservation method for long-term storage. Freeze-drying is generally preferred over other drying techniques as it gives a high-quality dehydrated product. However, to reach a high-quality product, many parameters need to be monitored, such as bacterial cell concentration, growth medium, lyophilization buffer, rehydration, and duration of freeze-drying. In this research, SA190 was freeze-dried with 10% sucrose mixed with 5% trehalose as lyophilization buffer. Pseudomonas argentinensis SA190 was isolated from the root nodules of the desert plant Indigofera argentae in Saudi Arabia, specifically Jizan. The SA190 freeze-dried product was examined by several tests to assess the product viability and quality, such as accelerated test and water stability test. For future work, the effect of freeze-dried SA190 on plant growth and crop yield will be investigated. Moreover, optimization of the freeze-drying process, formulation, and packaging for commercial will be considered. In addition, bacterial strains isolated in DARWIN21 project with promising effects on plant growth, will be subjected to freeze-drying process.

No description available.