This document discusses downy mildew of sorghum, caused by the soil-borne fungus Peronosclerospora sorghi. It causes significant yield losses globally. Symptoms include chlorotic or shredded leaves with white downy growth on the underside. It has both asexual and sexual phases. Oospores overwinter in soil and conidia spread the disease. Warm, humid conditions favor disease. Management includes crop rotation, resistant varieties, fungicides, and cultural practices to reduce inoculum.

1. STUDENT COURSE TEACHER
HARSHANA. P. V Dr. S. PARTHASARATHY
ID. No. 2016021012 Assistant Professor (Plant Pathology).
COLLEGE OF AGRICULTURAL TECHNOLOGY
Affiliated to Tamil Nadu Agricultural University, Coimbatore
Kullapuram, Via Vaigai dam, Theni-625 562
DOWNY MILDEW OF SORGHUM

2. DOWNY MILDEW
SIGNIFICANCE
• Sorghum Downy Mildew (SDM) is a highly
destructive disease caused by soil borne fungus
Peronosclerospora sorghi.
• It can have a significant economic impact, as infection
results in Plant death or lack of grain formation in
panicle.
• Sorghum Downy Mildew has been reported in 44
countries.

3. SIGNIFICANCE
• It is endemic in many parts of sub-Saharan Africa,
where it causes severe reductions in Corn and
Sorghum yield.
• The economic impact can be substantial as
systemically infected plants are sterile.
• This is demonstrated by the epidemics of Sorghum
Downy Mildew in Venezuela in the early 1970s,
which resulted in the epidemic being declared a
National emergency.

4. ECONOMIC IMPORTANCE
• Losses of US$ 2.5 million were caused in the coastal
countries of Texas, with incidence in individual fields
reaching 90% (Frederiksen et al., 1969).
• In India, Payak (1975) reported losses of 1, 00, 000
metric tons.

5. GLOBAL DISTRIBUTION
WORLD:
 Africa
 The Indian sub-continent
 South-East Asia
 North, Central and South America.

6. INDIA:
 Andhra Pradesh
 Delhi
 Haryana
 Karnataka
 Kerala
 Madhya Pradesh
 Maharashtra
 Rajasthan and Tamilnadu.
DISTRIBUTION

7. GLOBAL DISTRIBUTION OF SDM

8. SYMPTOMS OF SDM
• The fungus causes systemic downy mildew of
sorghum.
• It invades the growing points of young plants, either
through oospore or conidial infection.
• As the leaves unfold they exhibit green or yellow
colouration.

9. • Abundant downy white growth is produced on the
lower surface of the leaves, which consists of
sporangiophores and sporangia.
• Normally three or four leaves develop the chlorotic
downy growth.
SYMPTOMS OF SDM

10. • Subsequent leaves show progressively more of a
complete bleaching of the leaf tissue in streaks or
stripes.
• As the infected bleached leaves mature they become
necrotic and the interveinal tissues disintegrate,
releasing the resting spores (oospores) and leaving
the vascular bundles loosely connected to
give the typical shredded leaf symptom.
SYMPTOMS OF SDM

11. Pale yellow to light coloured streaked appearance
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12. Parallel stripes of green
and white tissues .
Shredded appearance.
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13. White (Downy)growth will
occur on the underside of
leaf tissue.
Brown- coloured lesions.
©Pioneer.com

14. Kingdom Chromista
Super Phylum Heterokonta
Phylum Oomycota
class Oomycetes
order Sclerosporales
Family Sclerosporaceae
Genus Peronosclerospora
Species P. sorghi
SYSTEMATIC POSITION
Peronosclerospora sorghi
(W. Weston & Uppal) C. G. Shaw, (1978)

15. Downy mildew/Leaf shredding of Sorghum
Crazy top - Sclerophthora macrospora (Sacc.)
Thirumalachar et al.
Syn. Sclerospora macrospora Sacc.
Sorghum downy mildew - Peronosclerospora sorghi
(W.Weston & Uppal) C. G. Shaw;
Syn: Sclerospora sorghi W. Weston &
Uppal

16. PATHOGEN -CHARACTERS
• P. sorghi is an obligate parasite systemic in young
plant.
• The mycelium is intercellular, non-septate.
• Sporangiophores emerge through the stomata in
single or in clusters which are stout and
dichotomously branched.
• Spores are single celled, hyaline, globose and thin
walled.

17. PATHOGEN
• Oospores are spherical, thick walled and deep brown
in colour.
• P. sorghi has polycyclic disease cycle.
• It is capable of causing secondary infection of the
susceptible hosts throughout the growing season.

18. Asexual phase:
 Conidia (15.0-28.9 × 15.0-26.9 µm) are hyaline,
thin-walled and suborbicular.
 Some conidia are in the process of germinating by
a single, unbranched hyphal germ-tube.
Sexual phase :
 Oospores (31.0-36.9 µm) are thick walled and
spherical.

19. Asexual phase Mature conidiophore
©icrisat.org

20. DISEASE CYCLE OF SDM
www.slideshare.net

21. EPIDEMOLOGY
MODE OF SPREAD
•
Primary Infection:
Oospores present in the soil. mycelium, seeds.
Secondary Infection:
Air-borne sporangia.
• infected heads land on the later emerging florets and infect
the frequent rain showers, high humidity and temperature. The
disease is internally seed borne, where pathogen infects the embryo in the seed.

22. FAVOURABLE CONDITIONS
• Relative humidity- 100%
• Optimum temperature 21-23 °C.
• Light drizzling.
• Cool weather.

23. MANAGEMENT
CULTURAL METHOD
• Growing non-host or host crops (For example, oat,
barley, flax, Sorghum sudanense or cowpea) for 15
days, and maize for 17 days reduced the inoculum
potential in soils infested with oospores.
• Deep tillage.
• Roguing of diseased plants will reduce the oospore
load in soil (Janke et al., 1983).

24. HOST- PLANT RESISTANCE
• Sorghum, although a self- pollinated species can be
induced to cross pollinate and thus lines with genetic
uniformity and complete resistance to Sorghum
Downy Mildew can be achieved (Frederiksen et al.,
1973).

25. BIOLOGICAL METHOD
• A Chytrid fungus (Gaertneriomyces sp.) was
identified parasitizing oospores of P.sorghi (Kenneth,
1982).
• It reduces incidence by upto 58% (Kunene et al.,
1990).
BOTANICAL METHOD
• Leaf extracts of Prosopis chilensis and
Azadirachta indica have also shown to have some
efficiency (Kamalakannan and Shanmugam, 2009).

26. RESISTANT VARIETIES:
Moderately Resistant varieties like
Co25
Co26.
TOLERANT VARIETY:
Paiyur 2
CSH 2
CSV 5

27. CHEMICAL METHOD
• Metalaxyl (Apron 35 SD) - Seed treatment @ 4g/kg
of seed.
• Foliar sprays will also prevent local lesions from
developing on Sorghum foliage.
• SAR agents including Phosphonic acid (Panicker and
Gangadharan, 1999) may be useful in managing the
disease where Metalaxyl resistance is problem.

28. REFERENCES
• Saha, L. R., 2015. Handbook Of Plant Diseases.
Kalyani Publishers, New Delhi.
• Das, P.C., 2018. Plant Diseases. Kalyani Publishers,
New Delhi.