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Plant/Microbe Interactions - Beneficial Interactions involving plant roots Interactions involving plant roots –Rhizoplane - the surface of the plant root,

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Presentation on theme: "Plant/Microbe Interactions - Beneficial Interactions involving plant roots Interactions involving plant roots –Rhizoplane - the surface of the plant root,"— Presentation transcript:

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2 Plant/Microbe Interactions - Beneficial Interactions involving plant roots Interactions involving plant roots –Rhizoplane - the surface of the plant root, root hairs present large surface area (> 6 m 2 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.

3 Plant/Microbe Interactions - Beneficial Interactions involving plant roots 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.

4 Plant/Microbe Interactions - Beneficial R/S ratio - indicates the importance of the root system to the microbial community. 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

5 Plant/Microbe Interactions - Beneficial In the rhizosphere (relative to root-free soil) 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 Reflects the influence of plant root exudates and the selection of organisms with high growth rates

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

7 Plant/Microbe Interactions - Beneficial Roots surrounded by active microbes produce more exudates than roots in sterile soil. 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. 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. As a plant grows the community in the rhizosphere changes to fast-growing, growth factor-requiring organisms.

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

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

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

11 Mycorrhizal Fungi

12 Mycorrhizae Tree root Mycorrhizal structure Fungal hyphae

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

14 Ectomycorrhizae

15 Plant/Microbe Interactions - Beneficial Ectomycorrhizae Ectomycorrhizae –found in most trees in temperate forests –benefits to the tree include: –drought resistance –pathogen resistance –enhanced nutrient uptake (PO 4 and K) –increased tolerance to pH changes –increased root growth

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

17 Plant/Microbe Interactions - Beneficial Endomycorrhizae 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

18 Plant/Microbe Interactions - Beneficial Endomycorrhizae 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.

19 Plant/Microbe Interactions - Beneficial Vesicular-Arbuscular (VA) Endomycorrhizae 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

20 Plant/Microbe Interactions - Beneficial Vesicular-Arbuscular (VA) Endomycorrhizae 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

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

22 Plant/Microbe Interactions - Beneficial

23 Vesicular-Arbuscular (VA) Endomycorrhizae Vesicular-Arbuscular (VA) Endomycorrhizae –benefits to the tree include: drought resistance drought resistance pathogen resistance pathogen resistance enhanced nutrient uptake (combined nitrogen, P, Zn, & Cu) enhanced nutrient uptake (combined nitrogen, P, Zn, & Cu) increased tolerance to pH changes increased tolerance to pH changes increased root growth increased root growth

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

25 Mycorrhizal Dependency Plant name RFMD (%) Cabbage (Brassicaceae) 0 Carrot99.2 Chicory (witloof) 82.4 Faba bean 93.5 Garden beet (Chenopodiaceae) 0 Garden pea 96.7 Kentucky blue grass 72.4 Kidney bean 94.7 Leek95.7 Pepper66.1 Potato41.9 Tomato (according cultivars) Sweet corn 72.7 Wheat (according cultivars)

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28 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

29 Inoculum Propagation Pot-culture 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 In vitro propagation on root-organ culture

30 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

31 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 In Vivo Propagation

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