3. Abstract
• The downy mildew diseases are caused by different fungus
species in several genera in the class Oomycetes.
• They comprise a major group of diseases affecting a large
number of crops.
• In India, downy mildews have been reported on several
economically important crops, including maize, sorghum,
pearl millet, onion, soybean, cucurbits, and grapes, causing
severe economic losses in some regions and seasons.
• Pathogens reported to cause downy mildews in India include
species in the genera, Perenosclerospora, Perenospora,
Pseudoperonospora, Plasmopara, Sclerophthora and
Sclerospora.
4. Grape downy mildew
Plasmopara viticola
• Irregular, yellowish,
translucent sports on
the upper surface of the
leaves.
• Correspondingly on the
lower surface, white,
downy growth on
fungus appear.
5. Symptoms
• Affected leaves become, yellow, brown and
gets dried.
• Premature defoliation.
• Dwarfing of tender shoots.
• Brown, sunken lesions on the stem.
• White growth of fungus on berries which
subsequently becomes leathery and shrivels.
• No cracking of the skin of the berries.
8. Mode of spread and survival
• Spread : Through sporangia by wind, rain etc.
• Survival : As oospores present in the infected
leaves, shoots and berries. Also as dormant
mycelium in infected twigs.
14. This is Arabidopsis-known as queen of biology, which
expresses small change in th e environment as circadian
rhythms and symptoms of any disease as indication of
presence of spores in the soil.
This can be exploited in plant pathology for research.
15. Downy mildew of crucifers and
cucurbits
• Downy mildew : Peronospora parasitica
All plant parts of crucifers can become
infected with this fungus.
18. • leaf symptoms are commonly observed.
• Black or dark specks appear on young leaves,
usually on the underside of the leaf first.
• Such spots are often irregular in shape and
may appear net-like.
• The upper side of the leaf will also develop
dark spots similar in shape and maybe
accompanied by leaf yellowing.
19. On older leaves, coalescence of these spots can occur,
resulting in larger areas of the leaf blade having large, sunken,
paper tan-colored spots.
21. Early infection on young plants can cause
stunting.
• On the underside of the leaf spots, a
white-grey, downy growth can be observed
with or without the aid of a hand lens, especially
when leaves are wet.
• On mature cabbage,
downy mildew can appear as dark sunken
spots on the head or wrapper leaves.
22.
23. • Often infections on the cabbage head will result in a
purplish tinge.
• Such infections predispose the plant to soft rot
bacteria or Sclerotiniose which can further rot
tissue in the field or after harvest.
24. Contd..,
• Cauliflower curds and broccoli heads can become
infected with blackened areas on the outside of
the tissue.
• The infection can become systemic and turn
inner curd and stem tissue dark.
• Radish and turnip “roots” can become infected
by spores that are washed down to the soil from
the leaves.
25.
26. • Symptoms might predominate on the upper part
of the root but the entire root is susceptible.
• Black spotting or a netted appearance can be
observed on the outside of the root but an
internal, firm rot can occur as well in some
situations.
• Some root distortion could occur, especially, if
infection occurred early in relation to root swelling.
• Flowers and seed stalks of cruciferous crops,
especially mustard, are also infected.
27. • With downy mildew of crucifers, however,
many sources of spores may exist.
• The life cycle of this disease is imperfectly
understood and resistant varieties may be
difficult to document, making it difficult to
recommend a long list of definitive non-chemical
controls.
28.
29. Favourable factors
Optimum temperature for the conidia is 8 to 10°C
For conidial germination 8 to 12°C and for host
penetration 16°C, rapid development 15 to 20°C.
30. Management :
Seed treatment with metalaxyl (Apron 35 S.D.)
6g/kg.
Spraying Metalaxyl + mancozeb combination
4g/litre or Mancozeb 0.25%.
31.
32.
33.
34. •Integrated disease management Cultural, chemical, and biological
control, and HPR are the components of integrated disease
management.
•Cultural control methods have been partially successful in most cases to
reduce the primary inoculum .Metalaxyl is an effective fungicide for all
downy mildews, but development of metalaxyl-resistant strains in some
downy mildew pathogens, including P. parasitica (Crute et al., 1985) has
posed a limitation on its widespread use.
•Biological control of downy mildews has so far been limited to
experiments and it will require substantial research efforts to achieve
any success.
•HPR offers the best opportunity to manage the downy mildews.
35. Recent advances in disease mgmt of DM
• DL-3-aminobutyric acid (BABA), a non-protein amino
acid, was found to induce resistance in melons and
cucumbers against downy mildew caused by the
fungus Pseudoperonospora cubensis.
• confirm the efficacy of the new strobilurin fungicdes
(Quadris, Flint, Cabrio) on downy mildew, but
pyraclostrobin (Cabrio) has been reported to be
highly effective in other states. Applications on 7-14
day intervals are recommended.
36. Forecasting Long-Range Transport of Downy Mildew
Spores and Plant Disease Epidemics
• The North American Plant Disease Forecast Center (NAPDFC)
located at North Carolina State University in Raleigh, NC, provides
continent-wide Internet forecasting support to tobacco and
cucurbit growers by tracking the geographic presence and future
spread of downy mildew pathogens.
• The two classical diseases forecasted are Tobacco Blue Mold and
Cucurbit Downy Mildew .
• During cool, wet, and cloudy weather, both pathogens increase
over time by producing large numbers of microscopic, asexual
propagules called sporangiospores (conidia) which can be aerially
transported both locally and long-distance via atmospheric wind
currents in the atmospheric boundary layer (ABL) (34).
37. • Using the principles and modern methods of related
sciences such as "aerobiology" and "biometeorology,"
the spatial and temporal pathways these spores travel
in the ABL can be forecasted and the future temporal
and spatial spread of the epidemics can be predicted.
• Biological and environmental factors, are used to
assess and report the risk level for new, distant
outbreaks.
• The principle differences between the NAPDFC
forecasting system and previous local forecasting
systems is two-fold:
• (1) aerial transport of spores inciting new outbreaks
are involved, and
• (2) the system addresses spore transport and weather
on a macroscale involving the entire North American
continent.
38.
39. • To asses that our forecasting is correct,there is
a system called DECISION SUPPORT SYSTEM,
which integrates the central library digital
photos and {relates it with virtual image of
spores which cause disease}, federal agencies,
growers and state co-ordinators, students and
scientists.
• Then analizes the data and gives it back.
41. The future research efforts on downy mildews in
India should focus on:
1.Distribut ion and mapping in various crops;
2.The role of weather factors on disease development
and spread;
3.The relative roles of asexual and sexual spores in
infection and disease spread;
4.Oospore survival under field conditions and the
influence of various cultural practices on their survival
and disease causing potential;
5.The importance of seed transmission and interstate
quarantine regulation;
42. Contd…
6.the genetics and mechanism of resistance;
characterization of resistance sources for genetic
makeup;
7.monitoring and characterization of pathogen
populations within India;
8.The use of molecular tools to better understand
genetics of host-pathogen interaction; and
9.Integ ration of control methods to develop an
effective and economic disease management
package.
