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Biotic Diseases

Biotic Diseases. Fungal diseases (cont.). Downy Mildew. A disease caused by a group of fungi belonging to the family Peronosporaceae class oomycetes. Infect a wide range of plants including grain crops, vegetables, field crops, ornamentals, shrubs and vines.

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Biotic Diseases

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  1. Biotic Diseases Fungal diseases (cont.)

  2. Downy Mildew • A disease caused by a group of fungi belonging to the familyPeronosporaceae class oomycetes. • Infect a wide range of plants including grain crops, vegetables, field crops, ornamentals, shrubs and vines. • Infection occurs through stomata on lower surface by sporangia itself or its zoospores, then mycelium spreads into the intercellular spaces. Finally, sporangia are produced on sporangiophores that emerge from stomata. • Sporangiophores form a visible mat of oomycete growth on lower side or both sides of leaves and other infected organs.

  3. Symptoms • At first, small pale yellow irregular spots appear on upper surface of leaves and a white downy growth of sporangiophores or oomycete appears on lower surface of spots. Spots of enlarge, coalesce forming large dead areas. • Later, infected leaf areas are killed and turn to brown while spots turn gray.

  4. Bremia lactuca onlettuce.

  5. Pathogen:Bremia lactuca Saucer shaped

  6. Plasmopara viticola on grape.

  7. Pathogen: Plasmopara viticola

  8. Perenospora parasitica on crucifers.

  9. Pathogen:Perenospora parasitica

  10. Powdery Mildew • A disease caused many species of fungi belonging to the family Erysiphaceae class Ascomycetes. The genera are distinguished by number of asci per cleistothecium and morphology of appendages. • Infect all plants except gymnosperms. • Infection starts when conidia fall on plant surface and germinate producing mycelium that spreads on plant surface not inside. Mycelium feeds by haustoria and produce conidia on short conidiophores on plant surface. In unfavorable conditions, the fungus produces cleistothecia containing one or more ascus.

  11. Cleistothecia

  12. Symptoms White to grayish powdery mildewy growth as patches or spots turns to yellow brown and finally black cleistothecia. Symptoms appear first on upper side of leaf then lower side. It also affects all plant organs.

  13. Erysiphe sp. on…….

  14. Pathogen:Erysiphe sp.

  15. Pathogen:Erysiphe sp.

  16. Leveillula taurica on artichoke.

  17. Pathogen:Leveillula taurica

  18. Uncinula necator on grapes

  19. Pathogen:Uncinula necator

  20. Sphaerotheca pennosa-rosa on roses

  21. Pathogen:Sphaerotheca pennosa-rosa

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