Susceptibility to Desiccation and Soil Factors Affecting the Survival of Rhizobium Japonicum Strains Radhi Kathum Al-Rashidi Iowa State University
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Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1978 Susceptibility to desiccation and soil factors affecting the survival of Rhizobium japonicum strains Radhi Kathum Al-Rashidi Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Agricultural Science Commons, Agriculture Commons, and the Agronomy and Crop Sciences Commons Recommended Citation Al-Rashidi, Radhi Kathum, "Susceptibility to desiccation and soil factors affecting the survival of Rhizobium japonicum strains " (1978). Retrospective Theses and Dissertations. 6365. https://lib.dr.iastate.edu/rtd/6365 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. 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Requests can be made to our Dissertations Customer Services Department. 5. Some pages in any document may have indistinct print. In all cases we have filmed the best available copy. Universi^ Microfilms International 300 N. ZEEB ROAD, ANN ARBOR, Ml 48106 18 BEDFORD ROW, LONDON WC1R 4EJ, ENGLAND 7907225 M-RfiSHIDI, RADHI K&TlUM SUSCEPTIBILITY TO DESICCATION AND SOIL FACTORS AFFECTING THE SURVIVAL OF RHIZOBIUM JAPONICUM STRAINS. IOWA STATE UNIVERSITY, PH.D., 1978 Universi^ Micrpfilnris International 300 n. zeeb road, amn arbor, mi 48to6 Susceptibility to desiccation and soil factors affecting the survival of Rhizobium iaponicum strains by Radhi Kathum Al-Rashidi À Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Departmenti Agronomy Major» Soil Microbiology and Biochemistry Approvedi Signature was redacted for privacy. arge of Major Work Signature was redacted for privacy. Fm the Major Department Signature was redacted for privacy. For the Graduate College Iowa State University Ames, Iowa 1978 ii TABLE OF CONTENTS Page INTRODUCTION 1 REVIEW OF LITERATURE 4 Factors Affecting Survival and Growth of Rhizobia in Soils 4 Soil factors 4 Soil moisture 4 Soil texture 6 Ionic composition 10 Temperature 12 Biological factors 15 Cell morphology 15 Cell water relations 16 Cell surface properties 17 Ecological adaptation 18 Production of extracellular polysaccharides 20 Microbiology of Irradiated Soils 21 Survival of Microorganisms in Irradiated Soils 22 Microbial Recolonization of Irradiated Soils 23 MATERIALS AND METHODS 25 Rhizobium iaoonicum Cultures 25 Rhizobium iaoonicum Culture Medium 25 Selective Media for Counting Rhizobia 25 Soils 26 Soil Analyses 26 Sterilization 27 Water Activity Measurements 28 Soil 28 Growth medium 29 iii Page Soil Factors Affecting the Survival of K. iaponicum strains 29 Survival of R. iaponicum Strains During Desiccation 31 Sand culture 31 Broth culture 31 Water Sorption Isotherms of R. iaponicum Strains 32 Apparatus 32 Sample preparation 33 Procedure 36 Nitrogen Fixation 39 Statistical Analysis 39 RESULTS AND DISCUSSION 40 Soil Characteristics Affecting the Availability of Soil Water to Microbes 40 Selective Media for Counting Rhizobia 42 Soil Factors Affecting the Survival of R. iaponicum Strains 44 Effect of salt 45 Effects of temperature and moisture 6l Susceptibility of R. japonicum Strains to Desiccation 73 Improving the Survivability of R. iaponicum Strains 87 Water Adsorption Isotherms 89 Bacterial Cell Morphology and Susceptibility to Desiccation 98 Application of the B.E.T. Theory 99 Changes in Rhizobia Surface Free Energy 104 iv Page SUMMARY AND CONCLUSIONS l06 LITERATURE CITED 109 ACKNOWLEDGMENTS 116 APPENDIX 117 1 INTRODUCTION Soybean (Glycine max L, Merr.) production is expanding rapidly throughout the world as a result of the high demand for the grain as an excellent source of oil and protein. For a long period the United States and China were the largest producers, far ahead of the other countries. However, soybean production recently in many countries has been expanding rapidly. In 20 years (1955-1975), the world area planted to soy beans has expanded from 80,000 to 8 million hectares. Consid ering an average of 70 kg of nitrogen fixed per hectare by symbiosis, an annual savings of 560,000 tons of nitrogen taken from the air instead of from the soil or fertilizer can be realized. Success in obtaining high fixation through the symbio sis of Rhizobium laconicum with soybeans depends on a series of factors which may interact increasing the complexity of the system: (a) effectiveness and efficiency of the R. iaponicum strains present in the inoculum and/or soil in rela tion to soybean varieties and the environment; (b) numbers of viable rhizobia cells in the inoculum compared to the native population of R. iaponicum; (c) techniques of inoculation and seeding to provide adequate survival and multiplication of rhizobia around the developing roots; (d) environmental factors, mainly soil factors, which will affect survival of the intro 2 duced rhizobia in soil, their establishment, rapid nodule initiation and/or functioning, and the physiology of the plant. The success of each stage is influenced to a considerable degree by the soil conditions surrounding the roots of the legume seedling. If soil conditions are unfavorable for the survival and growth of rhizobia prior to infection of the root hair, an effective nodule symbiosis will not develop. Rhizobia, like all other Gram-negative, nonspore forming bacteria, are more sensitive to certain environmental soil conditions than their host counterpart. Therefore, more in formation is needed about the survival of different R. iaponicum strains in different soils and the factors affecting their survival and adaptation. The purpose of this study was to evaluate the survival of different R. iaponicum strains in saline soils as developed in a hot dry climate. More specifically, the objectives were to: 1, Study the survival of two Australian and two Belts- ville R. Iaponicum strains in soils of different texture and organic matter contents. 2, Study the effect of temperature, salt concentration, and soil moisture content on the survival of differ ent R. iaponicum strains, 3, Examine the differences between the strains in terms of bacterial water relationships. study if the degree of survival of these strains can be improved by reducing the internal water content of the bacteria at low relative vapor pressure. 4 REVIEW OF LITERATURE Factors Affecting Survival and Growth of Rhizobia in Soils Soil factors Since the persistence of the rhizobia in soil is of im portance for the cultivation of legumes, it has been the sub ject of many studies. The survival and growth of root-nodule bacterial groups vary in different soils under a variety of environmental influences. Some of the soil characteristics affecting the survival and growth of rhizobia will be dis= cussed separately. It is realized that only rarely can a factor be considered in isolation; normally interaction occurs between a given factor and the other factors of the environment. Soil moisture Moisture content of the soil will af fect the activity of rhizobia in two ways. First, water is a major component of protoplasm, and second; an adequate layer of external water is necessary for maintenance of turgor and movement of substrates, toxic products, cells, etc. Therefore, as a soil dries and the soil moisture tension becomes greater, growth of rhizobia would decline and death would result. Fred et al. (1932) early reported on the loss of viability of rhizobia on the surface of inoculated seed. In a detailed study, Vincent et al. (1962) recognized two phases under dry ing conditions. The death rate was greatest during the first few hours of desiccation (approximately 24 hours) when the 5 main loss of water was occurring, and a storage period in which the death rate was reduced. They found that R. trifolii lost viability when suspended in distilled water and spread on glass beads under both drying (0 and 20% R.H,) and non- drying (100% R.H.) conditions. Suspension in 9% maltose ap peared to increase the survival of R. trifolii under desiccat ing conditions. Survival of R. meliloti in soil culture was studied by Jensen (1961). He reported survival in dry storage of up to 5x10^ cells/g soil after 30 to 40 'years in a medium containing sterilized loamy garden soil, calcium carbonate, and 5% mannitol.