DOWNY MILDEW FUNGI GENERA INCLUDES BREMIA AND PLASMOPARA, Downy mildew fungi are plant pathogens that cause significant damage to a variety of crops, including grapes, cucumbers, lettuce, and onions. These fungi thrive in cool, moist environments and can spread rapidly through a field, causing devastating losses for farmers. This slide deck provides an overview of downy mildew fungi, including their life cycle, symptoms, and management strategies. The presentation begins with an introduction to the various types of downy mildew fungi, including the species that affect grapes, cucumbers, and other crops. Next, the slides detail the life cycle of downy mildew fungi, from spore germination to the development of lesions on plant leaves. The presentation also explains how these fungi spread from plant to plant and from field to field, and highlights the conditions that favor their growth and reproduction. The slide deck then goes on to describe the symptoms of downy mildew infection, including yellowing and wilting of leaves, stunted growth, and the development of characteristic downy white or gray spores on the undersides of leaves. Finally, the presentation offers practical tips and strategies for managing downy mildew fungi, including cultural control measures such as crop rotation and sanitation practices, as well as chemical control methods such as fungicides. Overall, this slide deck provides a comprehensive overview of downy mildew fungi and their impact on agricultural crops, as well as practical strategies for preventing and managing these devastating plant pathogens.

1. ANNAMALAI UNIVERSITY
FACULTY OF AGRICULTURE
DEPARTMENT OF PLANT PATHOLOGY
PAT-501 MYCOLOGY
GENERAL CHARACTERS AND LIFE CYCLE OF GENUS PERONOSPORA ,
PSEUDOPERONOSPORA, PLASMOPARA , BREMIA , SCLEROSPORA ,
PERONOSCLEROSPORA
BY
R.LOKESH
I -M.sc.,Agriculture
Plant pathology
Annamalai university
TOPIC:
Part-2

2. GENERAL CHARACTERS OF PLASMOPARA
• P viticola made history in France in 1930 by devastating the grape vines.
• It is reported from India from all the grape growing areas.
• All the succulent parts are affected.
• Chlorotic patches appear on the upper surface of leaves making them
brittle,which fall off in shreds.
• In humid weath r downy growths (sporangiophores) emerge on the
lower leaf surface tendrils, pedicels, flowers, and fruits Infected fruits
shrivel and mummify

3. Scientific classification
Kingdom: Chromista
Phylum: Oomycota
Order: Peronosporales
Family: Peronosporaceae
Genus: Plasmopara
Species: P. viticola
Binomial name
Plasmopara viticola
(Berk. & M.A. Curtis) Berl. & De Toni, (1888)
DOWNY MILDEW OF GRAPES
• Plasmopara viticola, the causal agent
of grapevine downy mildew, is
a heterothallic oomycete that
overwinters as oospores in leaf litter
and soil.
• Plasmopara viticola, also known as grape
downy mildew, is considered to be the
most devastating disease of grapevines in
climates with relatively warm and humid
summers.
• It was first observed in 1834 by
Schweinitz on Vitis aestivalis in the
southeastern United States

4. Downy mildew on upper (left) and lower (right) surface of grape
leaves

5. SYMPTOMS
• Leaves show pale yellow spots on the upper
surface with white downy growth of the fungus
on the corresponding lower surface .
• Later, fungal growth becomes dirty grey and spot
becomes brown (necrosis). Necrotic lesion
coalesces to form larger patches resulting in
defoliation.
• Downy growth on the shoots and tendrils leads to
distortion and death of twigs.
• Infected flowers and berries will dry.
• Half grown infected berries become leathery,
wrinkle and develop a reddish marbling to brown
discoloration .

6. SYMPTOMS
• Leaves show pale yellow spots on the upper
surface with white downy growth of the fungus
on the corresponding lower surface .
• Later, fungal growth becomes dirty grey and spot
becomes brown (necrosis).
• Necrotic lesion coalesces to form larger patches
resulting in defoliation.
• Downy growth on the shoots and tendrils leads to
distortion and death of twigs.
• Infected flowers and berries will dry.
• Half grown infected berries become leathery,
wrinkle and develop a reddish marbling to brown
discoloration .

7. *This devastating disease led to the unexpected accidental discovery of Bordeaux mixture by Millardet.
*Bordeaux mixture (also called Bordo Mix) is a mixture of copper(II) sulphate (CuSO4) and quicklime (CaO)
used as a fungicide. It is used in vineyards, fruit-farms and gardens to prevent infestations of downy
mildew, powdery mildew and other fungi.
Bordeaux mixture in preparation

8. 1885 – The First Foliar Fungicide
Eight decades passed before a method of controlling
foliar disease was discovered; in 1885, P. M. A.
Millardet described the effective use of a mixture of
copper sulfate and lime for control of downy mildew
on grapevines.

9. LIFE CYCLE
Asexual reproduction
• Mycelium is hyaline, coenocytic, intercellular and produced globose haustona.
• Hyaline sporangiophores (4 - 6 or more) arise from the hyphae in sub stomatal
spaces / stomata in the lower surface of the leaves / lenticels (in case of fruits)
Sporangiophores branch almost at right angle to the main axis and at regular
intervals.
• From each branch, 2 or 3 secondary branches arise in a similar manner .
• From the apex of each secondary branch, 2 3 sterigmata arise to bear hyaline.
• Single celled, lemon shaped and thin sporangia singly.
• Sporangia germinate and produce zoospores (biflagellate), which encyst and
germinate to put forth mycelium.

10. • Sexual reproduction
• The fungus is heterothallic and hence two mating types (P1 and
P2) must be present for sexual reproduction.
• Spherical, thick, dull brown oospores are formed later in the
infected area due to the union of antheridium and oogonium.
• Oospores germinate after a period of rest and produce
zoosporangium.
• Zoospores are released from the sporangium, which start further
infection by putting forth germ tube.

11. Sporangium and spores of Plasmopara viticola
Lemon-shaped sporangia of Plasmopara viticola

13. GENERAL CHARACTERS OF BREMIA
• Bremia lactucae is a plant pathogen.
• This microorganism causes a disease of lettuce (Lactuca sativa)
denominated as downy mildew.
• Some other strains can be found on 36 genera of Asteraceae
including Senecio and Sonchus.
• Experiments using sporangia from hosts do not infect lettuce and it is
concluded that the fungus exists as a quantity of host-specific strains
(formae speciales).
• Wild species, such as Lactuca serriola, or varieties of Lactuca can
hold strains that infect lettuce, but these pathogens are not sufficiently
common to seriously infect the plant.

14. • Common name Lettuce downy mildew
• Scientific name Bremia lactucae
• Plants affected Lettuces
• Main symptoms Yellow blotches and white mould on
leaves
• Caused by Fungus-like (Oomycete) organism
• Timing Indoors any season, outdoors early summer
until mid-autumn
Lettuce downy mildew

15. Symptoms and Signs
• Downy mildew causes light green to yellow angular spots on
the upper surfaces of leaves.
• The white fluffy growth of the pathogen develops on the
lower sides of these spots.
• With time these lesions turn brown and dry up.
• Older leaves are attacked first.
• Severely infected leaves may die.
• On rare occasions the pathogen can become systemic,
causing dark discoloration of stem tissue.
• If downy mildew infects the cotyledons of young seedlings,
the plants can die.
Greenhouse-grown lettuce transplants can also be infected.

16. SYMPTOMS PHOTOS

17. REFERENCES
• https://www.apsnet.org/edcenter/disandpath/oomycete/pdlessons/
Pages/DownyMildewGrape.aspx
• https://en.wikipedia.org/wiki/Plasmopara_viticola#:~:text=Plasmopar
a%20viticola%2C%20also%20known%20as,in%20the%20southeaster
n%20United%20States.
• Introductory mycology – Alexopoulos
• An introduction to fungi – H.Dube
• https://en.wikipedia.org/wiki/Bremia_lactucae