1. Plant/Microbe Interactions - Beneficial
Interactions involving plant roots
Rhizoplane - the surface of the plant root, root hairs present large surface area (> 6 m2 for an average wheat plant). Only % of the rhizoplane is in direct contact with soil microbes.
Rhizosphere - the area of the soil directly influenced by plant roots (extremely variable). Soil that remains after shaking off roots.

2. Plant/Microbe Interactions - Beneficial
Interactions involving plant roots
Rhizosheath - some plants excrete a mucous-like material that cement sand grains together around the root. Most common in dry soils.

3. Plant/Microbe Interactions - Beneficial
R/S ratio - indicates the importance of the root system to the microbial community.
R  the number or biomass of microbes in the rhizoshphere.
S  the number or biomass of microbes in root-free soil.
R/S typically between 5 and 20, can be >100

4. Plant/Microbe Interactions - Beneficial
In the rhizosphere (relative to root-free soil)
abundance of Gram-negative rods is higher
abundance of Gram-positive rods and cocci is lower
Reflects the influence of plant root exudates and the selection of organisms with high growth rates

5. Plant/Microbe Interactions - Beneficial
Root exudates
amino acids (proteins)
keto acids (TCA cycle)
vitamins (enzyme co-factors)
sugars (C and energy)

6. Plant/Microbe Interactions - Beneficial
Roots surrounded by active microbes produce more exudates than roots in sterile soil.
The roots are not just leaky, there is an interaction with the microbial community.
As a plant grows the community in the rhizosphere changes to fast-growing, growth factor-requiring organisms.

7. Plant/Microbe Interactions - Beneficial
Microbial populations are clearly benefited by the interaction with roots but what does the plant get?
One major plant benefit is nutrient uptake . . .

8. Plant/Microbe Interactions - Beneficial
Mycorrhizae
mutualistic associations between fungi and plant roots
fungi become integrated into the root structure
both partners benefit (not a disease)

9. Mycorrhizal symbioses
Advantages:
Enhancing plant nutrient adsorption
Reducing soil born diseases
Improving plant water resistant

10. Mycorrhizal Fungi
Endophytes (similar to mycorrhizae) and polysaccharides secreted by the plant and fungi bind sand to the root.
Photo credit: Jerry Barrows, New Mexico State University, Las Cruces.
File names: BWSHEATH
COL-SH~1

11. Mycorrhizal structure
Mycorrhizae
Tree root
Photo credit: Randy Molina, Oregon State University, Corvallis.
File name: M4 Fungi LR.jpg, 328K
Fungal hyphae
Mycorrhizal structure

12. Plant/Microbe Interactions - Beneficial
Ectomycorrhizae
fungi form an external sheath on the root and extends into intercellular spaces (not inside individual cells)
approximately 40 mm thick
the root association can be up to 40% fungi by dry weight

13. Ectomycorrhizae
Photo Credit: USDA, Forest Service, PNW Research Station, Corvallis, Oregon.
File name: Ectomy~1

14. Plant/Microbe Interactions - Beneficial
Ectomycorrhizae
found in most trees in temperate forests
benefits to the tree include:
drought resistance
pathogen resistance
enhanced nutrient uptake (PO4 and K)
increased tolerance to pH changes
increased root growth

15. Plant/Microbe Interactions - Beneficial
Ectomycorrhizae
benefits to the fungus includes:
first access to plant exudates
direct benefit from trees photosynthetic activity

16. Plant/Microbe Interactions - Beneficial
Endomycorrhizae
fungal mycelia penetrate both between cells and inside individual cells
heath, rododendrons, laurels, orchids
the fungal partner does not fix nitrogen, but does seem to enhance the uptake of combined nitrogen

17. Plant/Microbe Interactions - Beneficial
Endomycorrhizae
orchids are pollinated at night and some mycorrhizal fungi are bioluminescent (insect attraction?)
rRNA sequence data place the origin of the endomycorrhizal fungi at or near the origin of land plants may indicate a long term co-evolution.

18. Plant/Microbe Interactions - Beneficial
Vesicular-Arbuscular (VA) Endomycorrhizae
the most common of all mycorrhizal associations
Phytobionts : 80% of plant species
wheat, corn, potatoes, beans, soybeans, tomatoes, strawberries, apples, oranges, grapes, cotton, tobacco, tea, coffee, cocoa, sugar cane, sugar maple, rubber . . .
Phylum : Glomeromycota
Genera: Glomus, Paraglomus, Sclerocystis, Acaulospora, Entrophospora, Gigaspora, Scutellospora, Diversispora, Geosiphon, and Archaeospora

19. Plant/Microbe Interactions - Beneficial
Vesicular-Arbuscular (VA) Endomycorrhizae
extensive network of mycelia that extends well out into the soil surrounding the root hair (vesicle and tree-like shapes)
arbuscules = tree-like
vesicles = intracellular fungal storage structures which are lipid containing bodies

20. Plant/Microbe Interactions - Beneficial
Colonization of a root by an endomycorrhizal fungus
(Brundrett et al Can. J. Bot. 63: 184).

21. Plant/Microbe Interactions - Beneficial

22. Plant/Microbe Interactions - Beneficial
Vesicular-Arbuscular (VA) Endomycorrhizae
benefits to the tree include:
drought resistance
pathogen resistance
enhanced nutrient uptake (combined nitrogen, P, Zn, & Cu)
increased tolerance to pH changes
increased root growth

23. Interaction of AM & Agricultural Practices
Fertilizer Application : High P
Crop Rotation : non-host plant species
Tillage : reduced / no tillage practices
Liming

24. Mycorrhizal Dependency
Plant name
RFMD (%)
Cabbage (Brassicaceae)
Carrot
99.2
Chicory (witloof)
82.4
Faba bean
93.5
Garden beet (Chenopodiaceae)
Garden pea
96.7
Kentucky blue grass
72.4
Kidney bean
94.7
Leek
95.7
Pepper
66.1
Potato
41.9
Tomato (according cultivars)
Sweet corn
72.7
Wheat (according cultivars)

27. Propagation cycle of AMF
a. Spores of (i) Gigaspora, (ii) Glomus, (iii) Entrophospora, and (iv) Acaulospora; b. germinating spore; c. hyphal network and spores; d. hypha and spores around root; e. hyphal penetration inside root; f. intracellular arbuscules; g. intraradical vesicles; h. colonized plant

28. Inoculum Propagation Pot-culture propagation
- Isolation of AMF pure culture strain : single spore
- Choice of a host plant : Allium porrum, Sorgum bicolor, Zea Mays, Paspalum otatum
In vitro propagation on root-organ culture

29. In Vitro Propagation
a. Isolated spores; b. germinating colonized root segment; c. carrot root in culture; d. AMF root-organ culture; e. closer view of an AMF root-organ culture

30. In Vivo Propagation
a. Seeding mycorrhizal substrates; b. mycorrhizal seedling production; c. growth chamber inoculum propagation; d. root growth and colonization; e. colonized seedlings; f. field inoculum propagation

31. End