Presentation on theme: "Plant/Microbe Interactions - Beneficial"— Presentation transcript:
1 Plant/Microbe Interactions - Beneficial Interactions involving plant rootsRhizoplane - 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 rootsRhizosheath - 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 higherabundance of Gram-positive rods and cocci is lowerReflects the influence of plant root exudates and the selection of organisms with high growth rates
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 Mycorrhizaemutualistic associations between fungi and plant rootsfungi become integrated into the root structureboth partners benefit (not a disease)
9 Mycorrhizal symbioses Advantages:Enhancing plant nutrient adsorptionReducing soil born diseasesImproving plant water resistant
10 Mycorrhizal FungiEndophytes (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: BWSHEATHCOL-SH~1
11 Mycorrhizal structure MycorrhizaeTree rootPhoto credit: Randy Molina, Oregon State University, Corvallis.File name: M4 Fungi LR.jpg, 328KFungal hyphaeMycorrhizal structure
12 Plant/Microbe Interactions - Beneficial Ectomycorrhizaefungi form an external sheath on the root and extends into intercellular spaces (not inside individual cells)approximately 40 mm thickthe root association can be up to 40% fungi by dry weight
14 Plant/Microbe Interactions - Beneficial Ectomycorrhizaefound in most trees in temperate forestsbenefits to the tree include:drought resistancepathogen resistanceenhanced nutrient uptake (PO4 and K)increased tolerance to pH changesincreased root growth
15 Plant/Microbe Interactions - Beneficial Ectomycorrhizaebenefits to the fungus includes:first access to plant exudatesdirect benefit from trees photosynthetic activity
16 Plant/Microbe Interactions - Beneficial Endomycorrhizaefungal mycelia penetrate both between cells and inside individual cellsheath, rododendrons, laurels, orchidsthe fungal partner does not fix nitrogen, but does seem to enhance the uptake of combined nitrogen
17 Plant/Microbe Interactions - Beneficial Endomycorrhizaeorchids 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) Endomycorrhizaethe most common of all mycorrhizal associationsPhytobionts : 80% of plant specieswheat, corn, potatoes, beans, soybeans, tomatoes, strawberries, apples, oranges, grapes, cotton, tobacco, tea, coffee, cocoa, sugar cane, sugar maple, rubber . . .Phylum : GlomeromycotaGenera: Glomus, Paraglomus, Sclerocystis, Acaulospora, Entrophospora, Gigaspora, Scutellospora, Diversispora, Geosiphon, and Archaeospora
19 Plant/Microbe Interactions - Beneficial Vesicular-Arbuscular (VA) Endomycorrhizaeextensive network of mycelia that extends well out into the soil surrounding the root hair (vesicle and tree-like shapes)arbuscules = tree-likevesicles = 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).
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 otatumIn vitro propagation on root-organ culture
29 In Vitro Propagationa. 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 Propagationa. Seeding mycorrhizal substrates; b. mycorrhizal seedling production; c. growth chamber inoculum propagation; d. root growth and colonization; e. colonized seedlings; f. field inoculum propagation