Pathology agricultural crop disease and management...

1. PAT 212 L 11.
Important Diseases of Sorghum,
Cumbu, Maize and Ragi

2. I. DISEASES OF SORGHUM

3. Whitish growth on
undersurface of leaves
1. Sorghum Downy Mildew
Peronosclerospora sorghi

5. Streaks of bleached leaves
Sorghum Downy Mildew
Local lesions on leaves

6. Sorghum Downy Mildew
Leaf shredding
Necrosis and drying of foliage

7. Pathogen
Systemic; obligate parasite; intercellular non-septate mycelium
Sporangiophores in clusters or in single – stout and dichotomously
branched at the tip, bear sporangia at the tip
Sporangia single celled, thin walled, hyaline, globose and lack papillae
Direct germination
Oospores abundant between fibrovascular strands of shredded leaves
thick walled, brown, round
Primary spread - Oospores in soil (viable for 3-4 years) and seed
Secondary spread - Air-borne sporangia

9. Management
The eradication of wild hosts near sorghum fields.
Destruction of plant debris by deep ploughing and other methods
Removal of infected sorghum plants in the field.
Crop rotation with pulses and oilseed crops
Growing mod. resistant varieties like Co 25 and Co 26
Seed treatment with Metalaxyl + mancozeb @ 4 g/kg of seed
Foliar spray of Metalaxyl @ 500 g/ha or Mancozeb @1 kg/ha or
zineb @ 1 kg/ha after the appearance of disease

10. Rust pustules
on leaves
2. Sorghum Rust – Puccinia purpurea
Symptoms
Young plants are rarely
affected by rust.
Scattered purple red,
or tan flecks appear on
both surfaces of leaves
(Fig.)
Typical rust pustules
appear on the lower
surface of leaves

11. When fingers are passed on such
leaves reddish powder can be seen on
the fingers.
In susceptible cultivars almost the
entire leaf tissue is destroyed
The pustules may also occur on leaf
sheaths and on inflorescence stalks.
Teliospores develop later in the same
uredosori or in a new teleutosori,
which are darker and longer
Sorghum Rust

12. Pathogen
Uredospore – pedicellate, elliptical or oval, thin walled, echinulate,
dark brown with 4-5 germ pores, paraphyses present
Teleutospores – pedicellate, reddish brown, two celled, round at
the apex with one germ pore in each cell, on germination
give promycelium bearing hyaline sporidia
Alternate host – Oxalis corniculata
MOS & S: Survive in the alternate host; air-borne uredospores
Management
Spraying of Mancozeb @ 0.2 %

13. Charcoal rot is a major disease in the sorghum growing in dry
regions.
Charcoal rot becomes conspicuous near crop maturity or
moisture stress during the pre-flowering period.
Fungus invades the crown via roots and disorganize the cortical
tissues of lower internodes
Bottom portion of stem becomes soft and weak which leads to
lodging and poor grain filling
If infected stem split open vascular fibres are seen to be clearly
separated and heavily coated with small hard black sclerotia,
hence named as charcoal rot
4. Charcoal rot of Sorghum – Macrophomina phaseolina

14. water-soaked lesions on roots
that turn brown or black
Lodging of plants

15. Pathogen
Sclerotia are black, 40 – 220 µm in size
MOS & S: Soil-borne sclerotia
Management
Maintaining soil moisture through irrigation, if possible,
during the post- flowering period can minimize charcoal rot
infestation.
Collection and destruction of infected crop residues
Treat the seed with Trichoderma viride at 4 g/kg

16. Grain smut / Kernel smut /
covered smut / short smut
Sporisorium sorghi
(Syn. Sphacelotheca sorghi)
Symptoms
Apparent only at grain formation
Normal grains are converted into sac
or sori and are oval or conical covered
with a tough white to light brown skin
(peridium), which persist up to
threshing.
Most of the grains are converted into
smut sori and they are larger than
normal grains
When the skin ruptures black powdery
mass of smut spores exposed.
Ratoon crops exhibit higher incidence

18. Pathogen
Centre of the sorus, a long hard column-like columella extending from base to
the apex, made up of host tissues including parenchyma and vascular strands
Space between columellum and sorus wall (peridium) is filled with black, dark
brown, powdery mass of smut spores
Smut spores (Teliospores) are thick-walled, smooth, round or oval, olive green
individually and viable for 10 years under laboratory conditions
On germination smut spore produces 4-celled promycelium and from each cell
single sporidium forms, which is spindle shaped
MOS &S
Externally seed borne (viable for more than 13 years) and air-borne spores
Low temp of 24oC and dry soil moisture (28 %) favour the disease incidence

19. Loose smut - Sporisorium cruentum (Syn. Sphacelotheca cruenta)
Symptoms
Normally all florets in infected head are smutted and can be seen
before earhead come out as they are shorter
Infected plants flower prematurely and show increased tillering and
affected plants are atleast one foot shorter than the healthy one
Inflorescences are looser and bushier with hypertrophied glumes
and often spikelet proliferation
The membrane of sorus ruptures and exposes spores
The centre of the sorus solid, long, black conical columella is seen,
which is more longer and more curved. It persists even after
the discharge of the spores

21. Pathogen
Membrane covering the sorus ruptures very early exposing the
spores even as the head emerges from the sheath
Long conical columella at the centre of sorus is more longer and
curved than the columella in grain smut and persists even
after the discharge of spores
The spores are round or shortly elliptical, dark brown than the
S. sorghi and the spore wall is pitted or echinulated
Teliospores germinate and form 4-celled promycelium and forms
sporidia only at low temperature. At high temp direct
germination is common
MOS & S
Externally seed-borne and soil-borne in dry regions
Fav. Temp. – 10-35oC

22. Head smut – Sporisorium holci-sorghi (Syn. Sphacelotheca reiliana)
Symptoms
Only few plants in a field are infected. It attacks the young
seedlings before the emergence from soil
Fungus is systemic and grows with the plant and covers the entire
floral tissues when they are formed
Head is either completely or partially replaced by a large whitish
gall (sorus)
The sorus first covered by whitish grey membrane of fungal
tissues, which ruptures before head emerges and expose
brown-black smut spores
Very rarely smaller sori develop on the leaves and lower part of the
peduncle

23. Pathogen
The smut spores are round or somewhat angular to spherical and
reddish brown to black with finely echinulate spore wall
MOS & Survival
Soil temperature: About 28oC
Soil moisture : 15-25 %

24. Long smut –
Tolyposporium ehrenbergii
Symptoms
Only few grains
are affected (because of
wind-borne infection)
The smut sori, which are
cylindrical, elongate, slightly
curved with creamy-brown
membrane (peridium)
The membrane ruptures and discharges black mass of spores and
exposes dark brown filaments, which represent the vascular
bundles of the infected ovary
The sori are considerably longer and wider than short smut

25. Pathogen
The spores usually aggregates to form spore balls,
which is difficult to separate
These spores are globose or angular, brownish green.
The epispore of the peripheral spores is densely with
warts
On germination of spores, sporidia are formed plenty
MOS & S
Air-borne sporidia

26. Mangement
• Early sown (June) crop escapes from disease
incidence
• Seed treatment with thiram @ 4 g/kg
• Crop rotation with non-host crop
• Field sanitation
• Mechanical removal of infected ear head
• Irungu cholam in Tamilnadu is free from long
smut

27. Symptoms
Harvesting / separating grain from
ergot-infected ear head can be
difficult.
Ergot contamination reduces grain
quality and limits its use as a
feedstock.
Ergot or sugary disease results
from the ergot fungus infects the
florets in the earhead (panicle) and
prevents seed set in such florets
Ergot / Sugary disease – Claviceps sorghi
(Syn. Sphacelia sorghi)
Ergot infested panicle

28. • The disease is confined to
individual spikelets and the
ovary is converted into
mass of fungal tissue and
grain formation is
prevented
• First symptom is the
secretion of honey dew
(creamy sticky liquid) from
infected florets
• If honeydew exudation is
profuse, it may drip down
and smear the whole
earhead, sometimes
dripping down onto the soil. Honey dew exuding from florets

29. Often, honey dew is colonized by a
fungus, Cerebella sp., which gives
the head a blackened appearance.

30. Later, long (1-2 cm),
straight or curved,
cream to light brown
hard sclerotia develop
Ergot infected earhead

31. Pathogen
Fungus produces septate mycelium
Honey dew (like) is a concentrated suspension of conidia, which are
single celled, hyaline, elliptic or oblong in shape and slightly
constricted in the middle and mycelial bits
Later stages sclerotia are formed. They are cylindrical, straight or
curved, hard black fungal mass (Ergot)
Mode of spread and survival
Survival as sclerotia, which germinate and produce ascus and
ascospores. Ascospores infect the ovary.
Sec. spread is through air and insect borne conidia. Rain splashes also
help in spreading the disease
Fav. Condition: Humid weather and continuous rain
Cool night temperature and cloudy weather

32. Management
• Sowing of ergot free seed.
• Sowing period to be adjusted so as to prevent heading during rainy
season and severe winter.
• Soaking seeds with 20% salt solution will aid to remove ergot
infested seeds, as such seeds will float in the salt solution.
• Seed treatment with fungicides such as Captan or Thiram @ 4g/kg.
• Spray Mancozeb @ 1000g/ha or Propiconazole @ 500ml/ha at
emergence of earhead (5 - 10% flowering stage) followed by a
spray at 50% flowering and repeat the spray after a week if
necessary

33. Witch weed – Striga asiatica
S. densiflora
Symptoms
Partial root parasite infecting
mainly the rainfed sorghum
Small plant (15-30 cm height)
occurs in clusters of 10-20/plant
S. asiatica produces red-pink
flowers
S. densiflora produces white
flowers
Each fruit contains minute seeds
which survive in soil for several
years

35. The root exudate of sorghum stimulate the seeds of the parasite
to germinate and infect
Severe infestation of the parasite causes yellowing and wilting
of the host plant
Infected plants are stunted and may die prior to seed setting
Management
Regular weeding and interculture operations during early stages
of parasitic growth
Spraying of sodium salt of 2, 4- D @ 45 g / 500 lit of water

36. II. Diseases of Cumbu
• Downy mildew
• Ergot/Sugary
disease
• Smut
• Rust
• Sclerospora graminicola
• Claviceps fusiformis
• T.penicillariae
• Puccinia penniseti

37. Downy mildew – Sclerospora graminicola
• Affected leaf exhibits white downy growth in patches on
its lower surface.
• These patches expand and cover the entire lamina which
turns yellow in due course.
• The downy growth consists of sporangiophores and
sporangia.
• Later the ear heads are converted into green leafy
structures either partially or fully.

38. Oospore
• The sporangia are single celled, hyaline, pear shaped
and are borne on stout sporangiophores.
• The oospores are spherical, smooth , thick walled and
serve as primary source of inoculum.

39. Management
• Deep ploughing so as to bury the Oospore deeply
• Rogue out infected plants
• Adopt crop rotation
• Use excess seed rate
• Growl resistant varieties like X 5, WCC-75 and Co 7
• Treat the seeds with Metalaxyl (Apron 35 SD) @ 6 g/kg
Spray Mancozeb @ 1 kg or Metalaxyl + Mancozeb
(Ridomil M Z) @ 2 kg /ha on 20th Day after sowing

40. Ergot/Sugary disease - Claviceps fusiformis
• Small droplets of pinkish sticky fluid oozes out of the
spikelets.
• The affected spikelets turn black and several such dark
sticky patches are seen on the earhead.
• Grain formation is inhibited. The honey dew (Like)
contains large number of hyaline single celled conidia
and mycelial bits.
• Later infected ovaries get converted into sclerotia.

41. Ergot of Cumbu

42. Management
• Adjust the sowing date so that the crop does not flower during
September when high rain fall and high RH favours the disease
spread.
• Immerse the seed in 10 % common salt solution and remove the
floating sclerotia
• Remove collateral host
• Spray Carbendazim @ 500g or Mancozeb @ 1.25 kg or Ziram
@ 1kg/ ha when 5 to 10 % flowers have opened and again at 50
% flowering stage

43. Smut –Tolyposporium penicillariae
• The disease becomes apparent at the time of grain set.
• A few grains, sporadically distributed on the earhead are replaced by
sori, which are much bigger than normal grains.
• The sori are green to black.
• The sorus wall is tough, surrounding the powdery mass of smut
spores which are in balls.
Managerment
• Removal and destruction of affected ear heads

44. Cumbu Smut

45. Rust - Puccinia penniseti
• Infection is seen in the form of brownish yellow
pustules on both the leaf surfaces.
• These represent the uredia of the fungus.
• The uredospores are oval, yellowish brown, sparsely
echinulate and pedicellate.
• Teliosori are black and seen on leaf and leaf sheath.
• Teliospores are dark brown, two celled and club
shaped. The fungus produces pycnial and aecial stages
on brinjal (the alternate host)
Management
• Spraying of Mancozeb @ 0.25%

46. III. DISEASES OF MAIZE

47. Downy mildew –
1. Sorghum downy mildew : Peronosclerospora sorghi
2. Rajasthan downy mildew - Peronosclerospora
heteropogoni
3. Brown stripe Downy mildew : Sclerophthora rayssiae
4. Crazy top - Sclerophthora macrospora

48. Sorghum downy mildew: Peronosclerospora sorghi
Symptoms
• Chlorosis, white stripes, stunting with downy
fungal growth on both leaf surfaces
• In susceptible seedling plants, less than 4 weeks
after seedling infection becomes systemic
• Malformation of tassels in infected plants

49. Systemic and obligate
Mycelium non-septate, inter cellular
Sporangiophore – base is stout , dichotomously
branched at the tip
Sporangia – single celled, thin walled, hyaline, globose
and lack papillae, germinate and produce germ tube
Oospores thick walled, thick brown and round
Mode of spread
Oospores in soil and seed-borne; Sec. spread by
sporangia
Sorghum Downy mildew - Peronosclerospora sorghi

51. Downy Mildew symptoms

52. Sorghum Downy mildew - Peronosclerospora sorghi

53. Proliferation of axillary buds on the stalks of the tassel and cob
Crazy top - Sclerophthora macrospora

54. Maize crazy top

55. Brown stripe Downy mildew : Sclerophthora rayssiae

56. 1. Leaf lesions only. In early stages of infection the leaves will
show narrow chlorotic or yellowish stripes 3-7 mm wide.
2. These lesions extend parallel with and are delimited by the leaf
veins and have well defined margins.
3. At later stages of infection, the chlorotic stripes take on a reddish
or purple color.
4. Severe striping and blotching occurs with confluence of adjacent
lesions.
5. Affected leaves remain intact and do not shred, even after severe
storms.
Primary inoculum comes from oospores overseasoning in the
soil or plant debris, or from mycelium in infected seed.
Oospores in air dried leaf tissue remained viable for four years
The pathogen apparently does not systemically infect the plant

57. • The eradication of collateral and wild hosts near maize
field and rouging infected maize plants
• Destruction of plant debris by deep ploughing and other
methods.
• Seed treatment with Metalaxyl @ 4 g/kg and foliar spray
of Mancozeb @ 2.5 g/l or Metalaxyl MZ @ 2g/l
• Use of resistant varieties like CoH(M)-5, DMR 1, DMR5
and Ganga 11.
Management- Downy mildew

58. Common Rust : Puccinia sorghi
Symptoms
• Brown pustules: Circular to elongate golden
brown or cinnamon brown, powdery, erumpent
pustules appear on both leaf surfaces.
• As the crop matures brownish black pustules
containing dark thick walled two celled teliospores
develop.
• In severe cases infection spreads to sheaths and
other plant parts

59. Rust - Puccinia sorghi
Oxalis leaves

60. Light orange coloured
pustules on Oxalis spp.
(Alternate host)

61. Pathogen
Heteroecious rust
Uredospores single celled, echinulate and yellowish brown
Teleutospores two-celled, slightly constricted at the septum,
rounded at the apex and dark brown in colour
Teliospores produce single celled basidiospores, which
infect three species of Oxalis viz., O. corniculata, O.
europaea and O. stricta
Aeciospores are carried by wind and infect maize
MOS
P.Source : Alternate host and S.Source : wind borne
uredospores

62. Rust Management
• Hybrids like Deccan, Ganga-5, Deccan Hybrid
Makka-103 and DHM - 1 are resistant to this
disease
• Spray Mancozeb @ 2.5g/lit (0.25%) as soon as
first symptoms are observed and it can be
repeated at 10 days interval till flowering.

63. Head smut – Sporisorium reilianum (Syn. Spacelotheca reiliana)
Symptoms
Systemic disease exhibit symptoms only at tasseling and silking
Abnormal development of tassels, become malformed and overgrown
Mass of black spores develop inside the male florets
Mass of black spores
replaces normal ear leaving
the vascular bundles
exposed and shredded.
Confined to inflorescence
only and no formation of
tumours as in common smut

64. Pathogen
Systemic
Chlamydospores or smut spores are angular to spherical, reddish
brown to black, finely echinulated and form promycelium
and sporidia
MOS and S:
Seed and soil-borne smut spores
Fav. Conditions: 20-30oC
Management:
Seed treatment
Crop rotation
(Follow recommendations given for the management of sorghum
smuts)

65. Charcoal-Rot : Macrophomina phaseolina
Symptoms
• The disease generally appears after flowering.
• Evidence of early-maturity .
• The out sides of lower internodes become straw coloured. The
pith becomes badly disintegrated.
• The infected stalks may split longitudinally into a mass of fibres.
• A distinguishing character - Presence of the small black
sclerotia in the pith of the affected stalks.
• Roots are also invaded and show black sclerotia in the
disorganised tissue.

66. Charcoal rot

67. Charcoal stalk rot – Macrophomina phaseolina
Small, black, sclerotial bodies found in rind and vascular
tissues
Disease occurs just before the emergence of the earhead

68. Stem rust on Barley crop
IV. Diseases of Ragi
1. Blast – Pyricularia grisea
Symptoms
Spindle shaped spots – drying of foliage – breaking of
midrib due to infection – node, earhead stalk and spikes are
also infected – chaffy grains or shrivelled grains
Pathogen: As in rice blast

69. Stem rust on Barley crop
Blast – Pyricularia grisea
Management
Treat the seeds with P. fluorescens 10 g/kg and spray the extracts
of Prosopis juliflora leaf extract (10%), Ipomoea cornea leaf
extract 10%
Spray Edifenphos 500 ml or Carbendazim 250 g or IBP 500 ml/ha.
Foliar spray with Aureofungin sol 100 ppm at 50% earhead
emergence followed by a second spray with Mancozeb @
1000g/ha 10 days later.