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Pathogenic Prokaryotes

Pathogenic Prokaryotes. Prokaryotes. Diverse group of over 30 genera DNA is not bound by a membrane Cytoplasm contains DNA and small (70 s) ribosomes Bacteria – cytoplasm surrounded by cell membrane and cell wall Mollicutes – cytoplasm surrounded by cell membrane.

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Pathogenic Prokaryotes

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  1. Pathogenic Prokaryotes

  2. Prokaryotes • Diverse group of over 30 genera • DNA is not bound by a membrane • Cytoplasm contains DNA and small (70 s) ribosomes • Bacteria – cytoplasm surrounded by cell membrane and cell wall • Mollicutes – cytoplasm surrounded by cell membrane

  3. Phytopathogenic Bacteria • Most phytopathogenic bacteria are rod shaped • Bacterial diseases favored by warm, moist environments • One genus, Streptomyces is filamentous • Slime layer – viscous, gummy layer around cell wall • Capsule – thick slime layer Scanning electron micrograph of rod-shaped bacteria

  4. Ecology of Phytopathogenic Bacteria • Some bacteria such as Agrobacterium tumefaciens and Streptomyces scabies are soil inhabitants • Most phytopathogenic bacteria are soil invaders • Erwinia amylovora has lost its ability to survive in soil

  5. Soil Invader vs Soil inhabitant • Soil invader can persist in the soil for a short time before populations decline whereas a soil inhabitant can persist in the soil as a stable population indefinitely.

  6. Rhizosphere vs Rhizoplane Rhizosphere Rhizoplane • Rhizosphere is the volume of soil that is influenced (biologically, chemically, or physically) by roots whereas rhizosplane is the surface of the root.

  7. Ecology of Phytopathogenic Bacteria • May be seed borne • Enter plants through wounds or natural openings – do not penetrate directly (except Streptomyces and Rhodococcus) • Spread by insects, rain, animals, humans, machinery

  8. Fire Blight - Erwinia amylovora

  9. Fire Blight • Bacteria over winter at margins of cankers and maybe in buds • Bacteria ooze out of openings and spread by insects • Dried ooze can break off and be spread by wind • Control is by resistance and copper or antibiotic sprays at bud break and during flowering

  10. Fire Blight - Disease Cycle

  11. Potato Scab – Streptomyces scabies

  12. Potato Scab • Pathogen is soil inhabitant • Most severe in near neutral to alkaline pH • Penetrates through wounds, natural openings and directly • Spread in soil water and by wind and infected tubers • Young tubers more susceptible than older ones • Overwinters in soil on plant debris and tissue

  13. Potato Scab – Disease Cycle

  14. Control of potato scab • Resistance • Lower soil pH • Use scab free seed pieces • Avoid moisture stress • Plant not susceptible crops (carrots, beets, radishes, small grains) in fields heavily infested with S. scabies.

  15. Crown Gall – Agrobacterium tumefaciens

  16. Crown Gall • Produces tumor-like growths on roots and stems • Bacteria enter through wounds • Soil-inhabitant • Discard symptomatic plants

  17. Tumor Formation • Virulent bacteria carry one to several large plasmids (organelle with small chromosomelike bodies composed of circular double stranded DNA) • Ti Plasmid – carries genes that determine the host range and types of symptoms produced • Introduced portion of Ti plasmid into plant DNA transforms cells • Opines – synthesized in transformed cells and can only be utilized by bacteria that have the appropriate Ti plasmid

  18. Rhodococcus fascians

  19. Rhodococcus fascians • Gram positive, aerobic bacterium • The only phytopathogen within its genus • Can penetrate plant without wounds or natural openings • Hard to isolate and grow in culture

  20. Black Rot of Cabbage – Xanthomonascampestrispv. campestris Can be seed borne Overwinter in debris and in/on seed

  21. Black Rot of Cabbage – Xanthomonascampestrispv. campestris V-shaped lesions; enters garden through transplants; spread by rain Can be seed borne Overwinters in debris and in/on seed

  22. Soft rot – Pectobacterium (Erwinia) carotovora

  23. Soft rot – Pectobacterium (Erwinia) carotovora A mushy, aromatic (it stinks) decay of succulent tissue in wet, warm weather

  24. Soft Rot • Survives on infected tubers, diseased plants or plant parts • Introduced on infected seed pieces or transplants • Can be spread by insects • Produce pectic enzymes • Serious problem in storage of tubers, cabbages, or other plant organs

  25. Soft Rot – Disease Cycle

  26. Control of soft rot • Delay harvest of tubers till the skin forms to avoid injury • Do not harvest when vegetables are wet or muddy • Remove soil before storing tubers • Keep storage area dry and cool

  27. Bacterial Wilt of Cucurbits – Erwiniatracheiphila

  28. Bacterial Wilt of Cucurbits – Erwiniatracheiphila

  29. Bacterial Wilt of Cucurbits • Soil invader • Spread by insects (cucumber beetles) • Cucumber, squash, muskmelon and pumpkin are susceptible

  30. Bacterial Streaming

  31. Bacterial Wilt – Disease Cycle

  32. Bacterial Wetwood

  33. Bacterial Wetwood • Caused by anaerobic bacteria that become trapped under callus • Usually isn’t fatal but can be a nuisance because ketones and alcohols in slime attract wasps and bees

  34. Bacterial ScorchXylella fastidiosa

  35. Bacterial Scorch • Symptoms include interveinalchlorosis and browning along leaf margins • Canopy shrinks • Transmitted by leafhoppers

  36. Bacterial Scorch • Improving tree vigor by fertilization and irrigation may extend life of tree • Injections with commercial brands of oxytetracycline may delay symptoms, but will not cure

  37. Diagnosis of Xylella sp. • Symptoms can be inconclusive • Elisa is commonly used • Bio Log can be used • Isolation of DNA and real time PCR becoming more commonly used

  38. Aster Yellows

  39. Aster Yellows • Transmitted by leafhoppers • Many herbaceous ornamentals such as marigold, coneflowers, asters, and zinnias are susceptible • Vegetables such as carrots are also susceptible • Transmitted by leaf hoppers

  40. Mollicute Life Cycle

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