biotic diseases
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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.
• 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.
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.
Bremia lactuca on lettuce.
Pathogen: Bremia lactuca
Saucer shaped
Plasmopara viticola on grape.
Pathogen: Plasmopara viticola
Perenospora parasitica on crucifers.
Pathogen: Perenospora parasitica
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.
Cleistothecia
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.
Erysiphe sp. on.……
Pathogen: Erysiphe sp.
Pathogen: Erysiphe sp.
Leveillula taurica on artichoke.
Pathogen: Leveillula taurica
Uncinula necator on grapes
Pathogen: Uncinula necator
Sphaerotheca pennosa-rosa on roses
Pathogen: Sphaerotheca pennosa-rosa