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 4 - 10% 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.

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.

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

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

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

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.

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 . . .

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)

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

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

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

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

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

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

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

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

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.

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

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

Plant/Microbe Interactions - Beneficial Colonization of a root by an endomycorrhizal fungus (Brundrett et al. 1985 Can. J. Bot. 63: 184).

Plant/Microbe Interactions - Beneficial

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

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

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) 59.2 - 78.0 Sweet corn 72.7 Wheat (according cultivars) 44.5 - 56.8

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

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

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

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

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