downy mildew is one of the major disease which cause yield loss

1. K.UTHAYANITHI
2017028088
Bsc (Hons) Agri

2.  DOWNY MILDEW IN MAIZE
Scleropthora rayssiae var. zeae
 DOWNY MILDEW OF SORGHUM
Peronosclerospora sorghi
 DOWNY MILDEW OF PEARL MILLET
Sclerospora graminicola

3. Brown stripe downy mildew
Scleropthora rayssiae var. zeae
 Symptoms
• Lesions start developing on lower leaves as narrow chlorosis or yellow stripes,3-7 mm wide,
with well defined margin and are delimited by the veins.
• The stripes later become reddish to purple. Lateral development of lesions causes sever striping
and blotching.
• Seed development may be suppressed, plant may die prematurely if blotching occurs prior to
flowering.
• Sporangia on the leaves appear as a downy whitish to wooly growth on both surface of the
lesions.
• Floral or vegetative parts are not malformed, and the leaves do not shred.

4. Small to large leaves are noticed in the
tassel. Proliferation of auxillary buds on the
stalk of tassel and the cobs is common (Crazy
top).

5.  Sporangiophores of indeterminate growth ,
 Sporangiophore is dichotomously branched ,
 Sporangia germinate by zoospores

6. Management
•Resistant varieties -Prabhat, Kohinoor, ICI-703, PAC-
9401, PMZ-2, SEEDTEC-2331.
•Seed treatment with Acylalanine fungicide metalaxyl
@ 6.0 g/kg.
•Rogue out infected plants at early stage.
•Control - Apron 35 WP, @ 2.5 g/kg as seed treatment.
•Spray with Metalaxyl 1g/lit or Metalaxyl + Mancozeb
@ 2.5 g/lit.

7. DOWNY MILDEW OF SORGHUM
Peronosclerospora sorghi
Whitish growth on the
undersurface of the leaves.
Streaks of bleached leaves
Leaf shredding

8. Pathogen
 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.
 Oospores are spherical, thick walled and deep brown in
colour
 .

9. Sporangiophore branching and Sclerospora type and
germination of sporangia is of like peronospora , Sporangia
are spherical without papilla

10.  Disease Cycle
 The primary infection is by means of oospores present in the soil
which germinate and initiate the systemic infection.
 Oospores persist in the soil for several years.
 Secondary spread is by air-borne sporangia. Presence of
mycelium of the fungus in the seeds of systemically infected
plants is also a source of infection.
 The disease has been known to occur through a collateral host,
Heteropogen centortus on which the fungus perpetuates of the
host.

11.  The breakdown of tissue causes shredding.
 The oospores either fall to the soil or are wind
blown, often within host tissue.
 They can remain viable in the soil for 5-10
years. Conidia are formed at night in large
numbers.
 The optimum temperature for production is
20-230C.

12. Favourable Conditions
Low temperature (21-33˚C)
High relative humidity (90 per cent)
and drizzling.
Young plants are highly susceptible.

13.  Management
 Crop rotation with other crops viz., pulses and oilseeds.
 Avoid the secondary spread of the disease by roguing out the infected
plants since the wind plays a major role in the secondary spread of the
disease.
 Grow moderately resistant varieties like Co25 and Co26.
 Seed treatment with Metalaxyl at 6 g/kg of seed.
 Spray Metalaxyl 500 g or Mancozeb 2 kg or Ziram 1 kg or Zineb 1kg/ha.

14. DOWNY MILDEW OF PEARL MILLET
Sclerospora graminicola

15. Symptoms
 pale, chlorotic, broad streaks extending from base to tip of leaves.
 At the advancement of disease, the leaf streaks turn brown and the leaves become shredded
longitudinally. In severe infection, the downy fungal growth can be seen on the upper as well as lower
surface of the leaves.
 The infected plants fail to form ear but if formed, they are malformed to green leafy structures.
 The complete ear can be transformed into leafy structure.
 The fungal pathogen transformed all floral parts such as glumes, palea, stamens and pistils into green
linear leafy structures of variable lengths.
 As the disease advances, the malformed floral structures of ears become brown and dry.

17.  Sporangiophore is dichotomously branched ,
Sporangia are lemon shape ,

18. Survival and spread
 The oospores remain viable for eight months to
ten years or more in the soil, which makes
primary infection in host plants and present
abundantly in diseased leaves fall on the ground.
 The secondary spread of disease starts from
sporangia, which are most active in moist
environment

19. Favorable conditions
 The atmospheric temperatures between 15-25 °C
and relative humidity above 85 per cent.
 Light drizzling accompanied by cool weather is
highly favourable

20. Management
 Grow downy mildew resistant varieties CO7, WCC 75,
CO(Cu)9, TNAU-Cumbu Hybrid-CO9
 Transplanting reduces disease incidence. At the time of
planting infected seedlings should be removed.
 In the direct sown crop, infested plants should be removed up
to 45 days of sowing as and when the symptoms are noticed.
 Spray any one of the fungicides Metalaxyl + Mancozeb @500 g
or Mancozeb 1000g/ha

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