Agricultural Microbiology

1. Rhizosphere and Phyllosphere
Dr. S. PARTHASARATHY, M.Sc. (Agri)., Ph.D.
Assistant Professor (Plant Pathology)

5. Rhizobium, Azotobacter, Clostridium
Beijerinckia, Pseudomonas, Alternaria

6. The rhizosphere is the narrow region of soil that is directly
influenced by root secretions, and associated soil microorganisms
known as the root microbiome.

7. The term Rhizosphere was introduced by the German scientist Hiltner in
1904.
The term rhizosphere is often divided into two general areas,
• the inner rhizosphere (very root surface) and
• the outer rhizosphere (immediate adjacent soil). The microbial
numbers are larger in the inner zone.
The endorhizosphere includes portions of the cortex and endodermis in
which microbes and cations can occupy the "free space" between cells
(apoplastic space).
The rhizoplane is the medial zone directly adjacent to the root including
the root epidermis and mucilage.
The outermost zone is the ectorhizosphere which extends from the
rhizoplane out into the bulk soil.

9. Rhizosphere effect
It indicates the overall influence of plant roots on soil microorganisms. It
can be put on a quantitative basis by the use of Root-Soil relationship.
Microbial interaction in rhizosphere
• Plant exudates are the main factors which influence the growth of
rhizosphere colonizers.
• Microorganisms present in the rhizosphere play important roles in
ecological fitness of their plant host

10. Functions
1. Decomposition of plant residue and organic matter
• Humus formation, mineralization of organic nitrogen, sulphur, and phosphorous
2. Increasing nutrient availability of phosphorous, magnesium, iron, zinc &
copper.
• Symbiotic mycorrhizal association, Production of organic chelating agents
• Oxidation-reduction reaction, Phosphorous solubilisation
3. Improve biological nitrogen fixation
• Free living bacteria and cyanobacteria
• Associative microorganisms
• Symbiotic legume and non-legume
4. Promoting plant growth
• Production of plant growth hormones, enhanced nutrient use efficacy
• Protection against root pathogens and pseudopathogens
5. Controlling deleterious microorganism
• Plant disease, nematodes and insects
6. Biodegrading synthetic pesticides and contaminants
7. Enhancing drought tolerance of plants
8. Improving soil aggregation

11. Functions

12. The term “phyllosphere” was first published by Dr. Jakoba Ruinen in 1961,. She
called the interface between leaves and air is “phyllosphere”, and said that this
was a much neglected milieu, compared to studies of the rhizosphere.
Subdivisions of phyllosphere
• They are caulosphere (stems),
phylloplane (leaves), anthosphere
(flowers), and carposphere (fruits).
• Phyllosphere is mainly inhabited by
bacteria, yeast, and fungi.
• Bacteria are found in numbers
averaging 106 to 107 cells/cm2 (up to
108 cells/g) of leaf.
• Some phylloplane microbes are able
to fix nitrogen (N) from atmospheric

13. Functions
1. Nutrient management
• Leaf nodulation - N fixation
• Cytokinin production
2. Disease management
• Protection against pathogens
• Induced systemic resistance
3. Environmental stress tolerance
• Control of ice nucleation-active bacteria.
• Protection through aggregation.

15. Thank
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