Ecology and Management of Plant Beneficial Microbial Communities

ECOLOGY AND MANAGEMENT OF PLANT BENEFICIAL MICROBIAL COMMUNITIES

Sponsoring Institution

National Institute of Food and Agriculture

Project Status

TERMINATED

Funding Source

HATCH

Reporting Frequency

Annual

Accession No.

0225891

Grant No.

(N/A)

Project No.

CA-R-ENS-5044-H

Proposal No.

(N/A)

Multistate No.

(N/A)

Program Code

(N/A)

Project Start Date

Nov 1, 2011

Project End Date

Oct 30, 2016

Grant Year

(N/A)

Project Director
Crowley, D.

Recipient Organization
UNIVERSITY OF CALIFORNIA, RIVERSIDE
(N/A)
RIVERSIDE,CA 92521

Performing Department
Environmental Sciences

Non Technical Summary
One of the principal goals of agricultural biotechnology has been to develop beneficial microorganisms for plant protection, nutrient uptake, and plant growth promotion. The idea of tailoring the species composition of the rhizosphere via application of soil inoculants dates back to more than a century ago with the first research on Rhizobium (Voelcker, 1896). Since that time, many different types of plant inoculants have been developed for agricultural biotechnology, including mycorrhizal fungi, plant growth promoting rhizobacteria (PGPR), phosphate solubilizing bacteria, and xenobiotic degrading bacteria for remediation of contaminated soils. Nevertheless, the practical use of most soil inoculants has been limited by inconsistencies that reflect our limited of knowledge of how specific inoculants interact with resident microbial populations (Haas and Keel, 2003). This problem is especially relevant to inoculation with PGPR bacteria as the genes encoding common PGPR functions are also carried by indigenous bacteria in the resident microbial community, and are regulated by quorum sensor mechanisms. The research described in this proposal is aimed at better understanding the interactions between PGPR inoculants and indigenous bacteria, and will study the effects of PGPR inoculation on both microbial community composition, and the expression of broadly distributed PGPR genes.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0110	1070	10%
102	0110	1100	20%
111	0110	1070	20%
111	0110	1100	10%
133	0110	1070	10%
133	0110	1100	30%

Knowledge Area
133 - Pollution Prevention and Mitigation; 102 - Soil, Plant, Water, Nutrient Relationships; 111 - Conservation and Efficient Use of Water;

Subject Of Investigation
0110 - Soil;

Field Of Science
1070 - Ecology; 1100 - Bacteriology;

Keywords

plant growth promoting bacteria

Goals / Objectives
One of the principal goals of agricultural biotechnology has been to develop beneficial microorganisms for plant protection, nutrient uptake, and plant growth promotion. The idea of tailoring the species composition of the rhizosphere via application of soil inoculants dates back to more than a century ago with the first research on Rhizobium (Voelcker, 1896). Since that time, many different types of plant inoculants have been developed for agricultural biotechnology, including mycorrhizal fungi, plant growth promoting rhizobacteria (PGPR), phosphate solubilizing bacteria, and xenobiotic degrading bacteria for remediation of contaminated soils. Nevertheless, the practical use of most soil inoculants has been limited by inconsistencies that reflect our limited of knowledge of how specific inoculants interact with resident microbial populations (Haas and Keel, 2003). This problem is especially relevant to inoculation with PGPR bacteria as the genes encoding common PGPR functions are also carried by indigenous bacteria in the resident microbial community, and are regulated by quorum sensor mechanisms. The research described in this proposal is aimed at better understanding the interactions between PGPR inoculants and indigenous bacteria, and will study the effects of PGPR inoculation on both microbial community composition, and the expression of broadly distributed PGPR genes. Objectives 1. Identify and characterize the predominant PGPR bacteria from indigenous and crop plant species in agricultural and arid zone soils in S. California. 2. Develop methods to monitor the copy number and activity of individual PGPR functions based on quantitative PCR and reporter gene constructs for conserved gene sequences that are shared across different genera of PGPR. 3. Determine the threshold and optimum population densities of PGPR and pollutant degrading bacteria that are required to improve plant tolerance to water stress, salinity, and crop yields. 4. Examine the effect of soil factors and agricultural management practices including use of soil organic amendments, biochar, pH, salinity, and nitrogen fertilizers on PGPR activity in soils. 5. Evaluate and develop inoculation methods for introduction of PGPR and pollutant degrading bacteria using biochar as a carrier for the inoculants, or by mass inundation using a field based fermenter.

Project Methods
Under objective 1, we will screen for PGPR or pollutant degraders using culture based methods that have been developed to identify bacterial colonies that degrade ACC, produce IAA, or degrade pollutants. Objective 2 is concerned with development of methods to quantify the copy number and activity of PGPR and organic pollutant degrading genes. For the PGPR research, this will include well known genes that have been shown to function for antibiotic and hydrogen cyanide production, ethylene destruction and auxin promotion. Among these, hydrogen cyanide and 2,4-DAPG production by PGPR pseudomonads are particularly important traits for disease suppression. Prior work has shown that the HCN genes are broadly distributed among many 2,4-DAPG producing pseudomonad strains (Haas and Defago, 2005). PCR primers for a conserved gene sequence in the hcnAB genes have already been designed by others and were shown to be specific and effective for detection of HCN producing pseudomonads from a world-wide collection of isolates (Svercel, et al., 2007). Similarly, primers are available to target production of 2,4-DAPG (Bergsma-Vlami). Another target gene will be the accA gene that encodes aminocyclopropane carboxylic acid deaminase. The accAgene is broadly distributed among a wide range of Gram negative bacteria including PGPR pseudomonads, and is also common in many Gram positive bacteria, rhizobia, and fungi (see review: Glick 2005). A fourth gene that we will track is the ipdC gene, which encodes for production of the plant growth hormone indole acetic acetic acid (IAA). Genes for the production of IAA are broadly carried by rhizosphere bacteria and it has been suggested that 80% of rhizosphere bacterial species produce IAA (see review: Spaepen et al. 2007). Under Objective 3, we will carry out experiments to examine the effective population size of PGPR and pollutant degraders. This will be examined using growth chamber experiments in which plants will be inoculated with different levels of PGPR or PAH degraders for which we have developed methods to quantify their populations using either an antibiotic resistance gene marker or a Q-PCR method that targets the intergenic region of the 16S-23S rRNA genes. Objective 4 evaluates the effects of specific environmental factors on PGPR activity. This will be accomplished using a model plant species in soils subjected to particular treatments and inoculated with a PGPR containing a reporter gene. Objective 5 aims at development of methods for introducing bacterial inoculants into the field, and will include studies on the use of biochar as an inoculum carrier, or mass inundation using a field fermenter. Previously charcoal has been shown to be an effective carrier for Rhizobium inoculants but biochar materials can be prepared at different temperatures and from different feedstocks that will influence its chemical and physical properties.

Progress 11/01/11 to 10/30/16

Outputs
Target Audience:Soil scientists and soil microbiologists who are working with the use of inoculants for agricultural biotechnology. Also of interest to scientists and groups who are interested in biochar and its affects on soil microbiology. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Technical training and professional development opportunities were provided to graduate students and visiting scientists who worked in the Crowley laboratory on different aspect of PGPR and soil inoculants. Professional development included seminars and presentations that were made at national and international meetings. How have the results been disseminated to communities of interest?Presentations and publication of technical journal articles. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Accomplishments of this research include the evaluation ofPGPR inoculants on plant salinity tolerance, the effects of biochar on soil microbial community compositions and evaluation ofthe use of biochar as a carrier for microbial inoculants. Specific experiments were conducted to examine the survival of model PGPB strains on biochar materials made from different feedstocks that were pyrolyzed at different temperatures to vary the surface area and porosity of the biochar matrix. Soil inoculation experiments were carried out to determine the movement of bacteria from char particles to the rhizosphere and subsequent colonization of the plant roots. Other research examined the use of microalginate beads and biochar mixtures for delivery of bacterial inoculants into soil. Collaborative projects with international cooperators were carried out to study the effects plant inoculation with phosphate solubilizing bacteria on plant and rhizosphere parameters of cereals grown under P deficiency. Crowley also carried out related research on development of artificial neural network modeling approaches for examining microbial community structures in soils and how soil microbial communities are affected by PGPR inoculants or the introduction of biochar into soils. These practical results will advance the use of microorganisms for agricultural biotechnology.

Publications

Type: Journal Articles Status: Published Year Published: 2016 Citation: Sun, D., L. Hale, D.E. Crowley. 2016. Nutrient supplementation of pinewood biochar for use as a bacterial inoculum carrier" Biology and Fertility of Soils. DOI 10.1007/s00374-016-1093-9
Type: Journal Articles Status: Published Year Published: 2015 Citation: Hale, L. and D.E. Crowley, 2015. DNA extraction methodology for biochar amended sand and clay. Biol. Fert. Soils. 51: 733-738.
Type: Journal Articles Status: Published Year Published: 2015 Citation: Barra, P.J., N.G. Inostroza, J.J. Acu�a, M.L. Mora, D.E. Crowley, M. Jorquera. Isolation of endophytic and rhizospheric bacterial consortia from avocado (Persea americana Mill.) and their effect on growth, biomass and superoxide dismutase activity of wheat seedlings (Triticum aestivum L.) under salinity stress. Appl Soil Ecol.
Type: Journal Articles Status: Submitted Year Published: 2016 Citation: Barra, P.J., N.G. Inostroza, M.L. Mora, D.E. Crowley, and M.A. Jorquera. Contribution of halotolerant bacterial consortia on salt and drought stress tolerance of avocado seedlings (Persea americana Mill.) in a commercial nursery.

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: Scientific community, soil scientists, soil and environmental microbiologists Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? This research provided training for a Ph.D. student, Lauren Hale, who carried out the bench research under my direction. How have the results been disseminated to communities of interest? Presentation at European Geosciences Union General Assembly April 27, 2014. Publication of research as a journal article in Applied Soil Ecology. Vol 84:192-199.  What do you plan to do during the next reporting period to accomplish the goals? Studies will be completed on the evaluation of biochar as a carrier for microbial inoculants. Visiting Ph.D. student from Chile (Patricio Barra from the Universidad de la Fronterra) will carry out research on endophytic bacteria associated with plant roots. Visiting Ph.D. student from China (Daquan Sun) will carry out research on methods to improve shelf life of bacterial inoculants. Manuscripts for journal publications will be prepared for final report.

Impacts
What was accomplished under these goals? Research conducted during this project period examined the suitability of different biochars as carriers for plant growth promoting bacterial inoculants and their relative efficacy in colonization of plant roots. Biochars were made from 5 feedstocks produced at 2 highest treatment temperatures (HTT's) by slow pyrolysis. Peat and vermiculite, which are traditional inoculum carriers, and liquid inoculum with no carrier, also were included for comparison. All of the carriers were inoculated with a liquid suspension of the plant growth promoting rhizobacterial (PGPR) strain, Enterobacter cloacae UW5, carrying a green fluorescent protein (GFP) marker. Inoculum survival was determined using quantitative PCR to enumerate the GFP markers in DNA extracted from non-sterilized soils directly after incorporation of the inoculated carriers and after a 4-week incubation. The biochars were characterized with respect to carbon and nitrogen content, specific surface area, pH, electrical conductivity, water holding capacity, pore opening diameters, and hydrophobicity to identify specific attributes that influence the survival of the inoculant after introduction into soil. The results indicated that chemical properties of biochar, particularly nitrogen and pH, were among the most important characteristics affecting initial inoculum survival and hence likely the shelf life. However, once incorporated into soil, physical features, including surface area, pore opening diameters, and water-filled pore spaces, were more closely associated with inoculum survival. All biochars tested performed as well as vermiculite and none demonstrated detrimental effects on the UW5 population. The best biochar was that made from pinewood at a HTT of 600 °C (Pine600), which performed as well as peat and sustained higher population densities than vermiculite. The Pine600 biochar was further tested to assess its effect on the expression of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and auxin synthesis, both of which were unaffected by the presence of biochar at 2% or 5% (w/v) concentrations.

Publications

Type: Journal Articles Status: Published Year Published: 2014 Citation: Hale, L., M. Luth, R. Kenney, D.E. Crowley. 2014. Evaluation of �pinewood biochar as a carrier of bacterial strain Enterobacter cloacae UW5 for soil inoculation. Applied Soil Ecology. 84:192-199.

Progress 01/01/13 to 09/30/13

Outputs
Target Audience: Farmers and orchard managers in California and the desert SW US who are interested in the effects of management techniques on the population size and activities of plant growth promoting bacteria in soils. This research should ultimately lead to methods for for improving plant stress tolerance. Local groups who are particularly interested in this research include avocado and citrus growers in California, and the California Avocado Commission. The research outputs are also targeted nationally and international to scientists and others who are interested in soil biology and practical applications of microorganisms for improving plant stress tolerance. Another target group are the undergraduate and graduate studentswho incorporate this knowledge through icoursework at UCR related to soil microbial ecology and plant production, as well as similar interest groups internationally who are involved in agricultural research. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? This research project has provided training and professional development for Ph.D. candidate Lauren Hale, who is working under the supervision of the PI. How have the results been disseminated to communities of interest? Results of the research examining biochar carriers for PGPB were presented at the Tri Society Meetings (Agronomy, Soil Science, and Crop Science) in Tampa, FL. The PI, Crowley, has also given seminars at international venues in Australia and China presenting synthesis results of artificial neural network models for describing the effects of environmental variables on microbial community structures in soils. What do you plan to do during the next reporting period to accomplish the goals? Our research will continue to focus on the development of a biochar carrier for plant growth promoting bacteria and how carrier materials affect the expression of functional genes that are related to plant growth promotion. In another avenue of research related to our modeling efforts to predict the populations of specific microorganisms, we are now exploring the use of topological data analysis for examining survival of bacterial populations. A visiting scientist cooperating with Crowley is also examining the role of PGPB on the development of mycorrhizal symbiosis with tomato plants. This fundamental work is aimed at examining the role of plant growth promoting bacterial inoculants on the suppression of plant production of the growth regulator ethylene, and the effects of ethylene on mycorrhizae colonization of roots.

Impacts
What was accomplished under these goals? Research conducted during this reporting period was aimed primarily at the development of biochar carriers for plant growth promoting bacteria (PGPB) that can be applied to soil to improve crop drought and stress tolerance. Specific experiments were conducted to examine the survival of model PGPB strains on biochar materials made from different feedstocks that were pyrolyzed at different temperatures to vary the surface area and porosity of the biochar matrix. Soil inoculation experiments were then carried out to determine the movement of bacteria from char particles to the rhizosphere and subsequent colonization of the plant roots. Other experiments examined the use of microalginate beads and biochar mixtures that examine the utility of these materials for delivery of bacterial inoculants into soil. Collaborative projects with international cooperators were also carried out to study the effects plant inoculation with phosphate solubilizing bacteria on plant and rhizosphere parameters of cereals grown under P deficiency. Crowley also is continuing the development of artificial neural network modeling approaches for examining microbial community structures in soils and their relationships to environmental variables.

Publications

Type: Journal Articles Status: Published Year Published: 2013 Citation: Ma. J., M.A. Ibekwe, D. Crowley, C-H. Yang. 2013. Influence of bacterial communities based on 454 pyrosequencing on the survival of Escherichia coli O157:H7 in soils. FEMS Microb. Ecol. 84:542-554. Liu, Y., G. Pan, X. Yu, X. Zhang, D. Crowley, Q. Hussain, L. Li, D. Liu, J. Zheng, T. Zhou, J. Zheng. 2012. Decline in topsoil microbial quotient, fungal abundance and C utilization efficiency of rice paddies under heavy metal pollution across South China. PloS One 7:e38858. Santos, E.C., E.D. Armas, D.E. Crowley, M.R. Lambais. 2014. Artificial neural network modeling of microbial community structures in the Atlantic Forest of Brazil. Soil Biol. Biochem. 69:101-109.

Progress 01/01/12 to 12/31/12

Outputs
OUTPUTS: In the first year of this project, research was conducted to better understand the interactions between plant growth promoting rhizobacteria (PGPR) inoculants and indigenous bacteria. Collaborative research was conducted with colleagues in Australia to develop DNA microarray methods for soil microbial community analysis. We further examined factors affecting microbial activity and biomass in relation to soluble carbon levels in soil. PGPR populations were examined in the rhizosphere of Larrea tridenta to assess their possible role in stress tolerance by desert plants that are adapted to drought and high temperature. Related research examined the population densities of PGPR in the rhizosphere of avocado and possible effects of salinity on their population and activity. Research conducted with colleagues in Chile was conducted to study functional genes in PGPR that are associated with phosphorus solubilization. A mathematical simulation model was developed to examine how PGPR colonize plant roots and their response to local variations in carbon substrate availability in the rhizosphere. Collaborative research examined the potential role of rhizobacteria for facilitating selenium uptake by plants in selenium deficient soils. Other collaborative research with colleagues in China reports the entire genome sequence of a plant growth promoting bacterium from vineyard soils. Associated outputs include the mentoring of graduate students and postdocs who carried out the bench research on the above projects. The research describe above has been reported in 8 journal publications, and was presented in seminars and international talks, including talks delivered in Chile, Israel, and China at Beijing Agricultural University, Nanjing Agricultural University, and Zeijiang University. In local outreach activities, highlights of this research were also presented to several hundred citrus growers at the California Citrus Conference in Porterville, CA in October 2012, and at the Turfgrass Field Day event on the UCR campus (led by Dr. Jim Baird at UCR) . The results of this research have also been incorporated into class materials for courses in Soil Conditions and Plant Growth and Soil Ecology, taught by Crowley at UCR. Parts of this research were also incorporated into a 3 day workshop on advances in soil biology at the Universidad de la Fronterra in Temuco, Chile. PARTICIPANTS: Foreign Collaborators: Milko Jorquera (Professor, UFRO, Temuco Chile); Oscar Martinez (Ph.D. student, UFRO Temuco Chile), Prof. Dr. Mary Lu Mora (UFRO, Temuco, Chile); Pauline Mele (Professor LaTrobe University, Australia,); Ross Chapman (Staff Scientist Victoria, Department Primary Industries, Victoria, Australia); Dr. Helen Hayden (Postdoc DPI, Victoria, Australia). Professor Muhammad Arshad (University of Agriculture, Islamabad, Pakistan), Dr. Alan Richardson (CSIRO, Canberra, Australia); J. Ziwei, L. Li, D. Wu, Y. Wang, and W. Wu (China Agricultural University); Professor Zed Rengel (University of Western Australia, Perth Australia). National Collaborators: Dr. Mark Ibekwe (USDA Salinity Lab, Riverside, CA); Professor Ching Hong Yang (University of Wisconsin, Madison, WI). Visiting Scientists: Sajid Nadeem (visiting scientist, University of Arid Agriculture, Faisalabad, Pakistan: Dr. Yanbin Guo (one year sabbatical China Agricultural University). Postdoctoral associates: Dr. B. Shaharoona (postdoc UCR); Jincai Ma (USDA Salinity Lab, Riverside, CA). Graduate Students: Lauren Hale (UCR); Julie Escalera (UCR); TARGET AUDIENCES: Farmers and orchard managers in California and the desert SW US who are interested in the effects of management techniques on the population size and activities of plant growth promoting bacteria in soils. This research should ultimately lead to methods for for improving plant stress tolerance. Local groups who are particularly interested in this research include avocado and citrus growers in California, and the California Avocado Commission. The research outputs are also targeted nationally and international to scientists and others who are interested in soil biology and practical applications of microorganisms for improving plant stress tolerance. Another target group are the undergraduate and graduate students who incorporate this knowledge through icoursework at UCR related to soil microbial ecology and plant production, as well as similar interest groups internationally who are involved in agricultural research. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
This research is leading to new fundamental knowledge on the role of PGPR in plant stress tolerance. The research is also providing information on the effects of soil management practices and environmental factors on the abundance and activity of PGPR that can be used to optimize plant beneficial microbial interactions. The long term expected outcome will be application of the knowledge from this research for improvement of crop productivity in saline soils and possibly, the development of inoculants that may be used to improve plant stress tolerance. The research has further stimulated new ongoing projects that are examining the use of biochar materials for delivery of soil inoculants, and the effects of biochar on the populations and activity of indigenous PGPR.

Publications

Jorquera, M.A., B. Shaharoona, S.M. Nadeem, M. Arshad, and D.E. Crowley. 2012. Rhizosphere bacteria associated with the 11,700 year-old King Clone of Larrea tridentata. Microbial Ecology. 64:1008-1017.
Nadeem, S.M., B. Shaharoona, M. Arshad, and D.E. Crowley. 2012. Population density and functional diversity of plant growth promoting rhizobacteria associated with avocado trees in saline soils. Appl. Soil Ecol. 62:147-154.
Jorquera, M.A., N. Saavedra, F. Maruyama, A.E. Richardson, D.E. Crowley, R.C. Catrilaf, E.J. Henriquez, and M.L. Mora. 2012. Phytate addition to soil induces changes in the prevalence of Bacillus B-propeller phytase genes in the rhizosphere. FEMS Microbiol. Ecol. 83:352-360.
Muci, A.L., M.A. Jorquera, A.L. Avila, Z. Rengel, D.E. Crowley, and M.L. Mora. 2012. A combination of cellular automata and agent-based models for simulating root surface colonization by bacteria. Ecol. Modeling. 247:1-10.
Chapman, R., H.L. Hayden, T. Webster, D.E. Crowley, P.M. Mele. 2012. Development of a microarray approach for measurement of microbial functional genes associated with soil health in Australian agroecosystems. Pedobiologia 55:41-49.
Ma, J., M.A. Ibekwe, M. Leddy, C-H. Yang, and D.E. Crowley. 2012. Assimilable organic carbon (AOC) in soil water extracts using Vibrio harveyi BB721 and its implication for microbial biomass. PLoS One. 7:e0028519.
Acuna, J.J., M.A. Jorquera, P.J. Barra, D.E. Crowley, and M.L Mora. 2012. Selenobacteria selected from the rhizosphere as a potential tool for Se biofortification of wheat crops. Biol. Fert. Soils. 49:175-185.
Guo, Y., J. Ziwei, L. Li, D. Wu, D. Crowley, Y. Wang, and W. Wu. 2012. Draft genome sequence of Rahnella aquatilis strain HX2, a plant growth-promoting rhizobacterium isolated from vineyard soil in Beijing. J. Bacteriol. 194:6646-6647.

Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: This research is examining the ecology of plant growth promoting rhizosphere-bacteria (PGPR) and their contribution to plant survival under arid and saline soil conditions and to plant mineral nutrition in nutrient poor soils. One study has been completed in which we have examinted the impacts of nitrogen fertilization on the population and activity of PGPR in paste soils. Another study that was completed during this first year has examined the populations of PGPR that associated with the 11,400 year old King Clone of Larrea tridenta, which has survived in an arid habitat for millenia. A manuscript reporting this research is now in the final stages of review with final revisions before it will be published as a technical journal article. Results of this research also have been report (output) in seminars delivered at several venues including the University de la Fronterra, Temuco, Chile, and lectures given at the China Agriculture University and other venues in China. Other research has also been conducted to examine the role of PGPR in salinity tolerance of avocado, which was presented to avocado growers at a series of meetings sponsored by the California Avocado Commission. That research also has been submitted for publication. Other research in progress will lead to manuscripts on the role of enzymes produced by PGPR for solubilization of organic phosphates in soils. PARTICIPANTS: Visiting scientsts: Milko Jorquera (UFRO, Temuco Chile), Oscar Martinez (UFRO Temuco Chile), Dr. B. Shaharoona (postdoc UCR), Sajid Nadeem (visiting scientist, University of Arid Agriculture, Faisalabad, Pakistan: Dr. Yanbin Guo (one year sabbatical China Agricultural University). Graduate Students: Lauren Hale (UCR). TARGET AUDIENCES: Farmers and orchard managers in California and desert SW US who are interested in management techniques for improving the biological function of soil microbial communities for improving plant stress tolerance. California Avocado Commission. International academics and researchers interested in soil biology and applications for improving plant stress tolerance. Undergraduate and graduate students in coursework at UCR related to soil microbial ecology and plant production, as well as similar interest groups internationally. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
This research is leading to new fundamental knowledge on the role of indigenous PGPR in plant stress tolerance. The research should also provide information on the effects of soil management practices and environmental factors on the abundance and activity of PGPR. As the research has only just begun this past year, there has not yet been sufficient time to determine the impact of this research. The long term expected outcome will be application of the knowledge from this research for improvement of crop productivity in saline soils and possibly, the development of inoculants that may be used to improve plant stress tolerance.

Publications

Martinez, O., M.A. Jorquera, D.E. Crowley, M.L. Mora. 2011. Influence of nitrogen fertilisation on pasture culturable rhizobacteria occurrence and the role of environmental factors on their potential PGPR activities. Biology and Fertility of Soils. 47: 875-885.