1. DOWNY MILDEW OF SORGHUM
COLLEGE OF AGRICULTURAL TECHNOLOGY
(Affiliated to Tamil Nadu Agricultural University, Coimbatore-3)
Kullapuram (Po),ViaVaigai Dam, Theni-625 562
STUDENT
Miss. DHANUJA N
ID. No. 2015021029
COURSE TEACHER
Dr. PARTHASARATHY S
Asst. Professor (Plant Pathology)
2. DOWNY MILDEW OF SORGHUM
OTHER NAME:
Leaf shredding disease
LOCAL NAME:
Adi Saambal Noi (Tamil)
COMMON NAME:
Mildew of Maize and Sorghum
4. IMPORTANCE:
Sorghum downy mildew (SDM) is a highly destructive
disease caused by the soil borne fungus Peronosclerospora
sorghi.
It can have a significant economic impact, as infection
results in plant death or lack of grain formation in the panicle.
5. HISTORY:
P. sorghi was introduced to the Americas in the mid to late
1950s, probably in the Central American region, possibly Panama
(Toler et al., 1959; Futrell, 1974).
It reached the USA in the early 1960s (Reyes et al., 1964)
and has subsequently spread to many other countries in Central
and South America.
6. HISTORY:
P. sorghi is widespread in Africa and Asia (Williams,
1984; Jeger et al., 1998).
It is thought that the pathogen co-evolved on sorghum in
Africa (Williams, 1984) although other theories suggest Asia
(Shaw, 1981; Weltzein, 1981).
It can be considered endemic on these two continents.
7. ECONOMIC IMPORTANCE:
The economic impact can be substantial as systemically
infected plants are generally 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 (El Nacional,
Venezuela, August 2, 1975, in Frederiksen and Renfro, 1977).
8. ECONOMIC IMPORTANCE:
Losses of US$ 2.5 million were caused in the coastal
counties of Texas, with incidence in individual fields reaching
90% (Frederiksen et al., 1969).
In India, Payak (1975) reported losses of 100,000 metric
tons.
9. DISTRIBUTION:
WORLD:
P. sorghi exists in Africa, the Indian sub-continent, South-
East Asia and North, Central and South America.
INDIA:
Andhra Pradesh, Delhi, Haryana, Karnataka, Kerala,
Madhya Pradesh, Maharastra, Rajasthan, Tamil Nadu.
11. SYMPTOMS:
There are two types of symptom produced by P. sorghi in
both sorghum and maize (Schuh et al., 1986).
Systemic infection which occurs by oospores or conidia
during the first four weeks of germination of the seed.
Local lesions resulting from conidial infection of older
plants, which may also give rise to systemic infection.
12. SYMPTOMS:
The fungus invades the growing points of young plants,
either through oospore or conidial infection.
As the leaves unfold they exhibit green or yellow
colouration.
Abundant downy white growth is produced on the lower
surface of the leaves, which consists of sporangiophores and
sporangia.
13. SYMPTOMS:
Normally three or four leaves develop the chlorotic
downy growth.
Subsequent leaves show progressively more of a complete
bleaching of the leaf tissue in streaks or stripes. As the infected
bleached leaf matures they become necrotic and the interveinal
tissues disintegrate, releasing the resting spores (oospores).
This leaves the vascular bundles loosely connected to give
the shredded leaf symptom.
20. PATHOGEN:
Personosclerospora sorghi has a polycyclic disease cycle.
It is capable of causing secondary infection of the
susceptible hosts throughout the growing season.
21. Asexual phase:
Conidia (15.0-28.9 x 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.
25. MODE OF SPREAD:
Primary Infection :
Oospores present in the Soil, Mycelium, Seeds.
Secondary Infection:
Air-borne sporangia.
26. LIFE CYCLE:
The oospores are present in the soil when the host
seedlings are germinating.
They infect the roots of the seedlings.
This is a systemic infection.
The pathogen grows throughout the plant, infecting the
leaves as they grow, leading to chlorosis.
27. LIFE CYCLE:
The chlorotic leaves develop white streaks.
When the oospores become mature, the white streaks on
the leaves turn brown and become necrotic.
These necrotic areas become shredded over time, which is
how the mature oospores are disseminated.
28. LIFE CYCLE:
As the pathogen continues to develop in the host plant,
there may also be production of conidia on the leaf surface.
This cause the white, downy growth on the undersides of
the leaves.
After they are released, they are wind disseminated.
29. MANAGEMENT
Cultural methods:
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.
30. Biological Control:
A Chytrid fungus (Gaertneriomyces sp.) was identified
parasitizing oospores of P. sorghi (Kenneth, 1982).
It caused a reduction in the incidence by up to 58% by
parasitizing the soil-inhabiting oospores (Kunene et al., 1990).
31. Botanical Control:
Leaf extracts of Prosopis chilensis and Azadirachta indica
have also shown to have some efficiency (Kamalakannan and
Shanmugam, 2009).
33. Chemical Control:
The fungicide Metaloxyl is efficient in reducing the
systematic infection of downy mildew when applied as seed
dressing.
Seed treatment followed by two foliar sprays at 10 and 40
days after emergence completely controls the disease.
