A detailed description of rice diseases has been furnished in an easy manner

1. Diseases of Rice
N. H. SHANKAR REDDY
Ph.D., Plant Pathology
Annamalai University

2. Important diseases of rice
DISEASES CAUSAL ORGANISM
FUNGAL DISEASES
Blast Pyricularia oryzae
Brown spot or Sesame leaf spot Bipolaris oryzae
(Helminthosporium oryzae)
Sheath blight Rhizoctonia solani
Sheath rot Sarocladium oryzae
Stem rot Sclerotium oryzae
Foot rot or Bakanae disease Fusarium moniliforme
False smut Ustilaginoidea virens
Udbatta disease Ephelis oryzae
Grain discolouration Complex disease

3. BACTERIAL DISEASES
Bacterial leaf blight(BLB) Xanthomonas oryzae pv. oryzae
Bacterial leaf streak Xanthomonas oryzae pv.
oryzicola
VIRAL DISEASES
Tungro Rice tungro virus [RTV]
Grassy stunt Rice grassy stunt virus
Dwarf Rice dwarf virus
Yellow dwarf Phytoplasma like organisms
Rice khaira Zn deficiency

4. 1. Rice blast - Pyricularia oryzae (Magnaporthe
grisea)
Symptoms
• Typical spindle to diagonal, both end pointed (different from brown
spots), reddish brown margin and the center is grayish white (strw
colour).
• The pathogen produces three different symptoms viz., leaf blast, nodal
blast and neck blast.

5. Leaf blast
• Susceptible at
Seedling stage
Tillering stage
Panicle initiation stage
• On the leaves, spindle shaped spots are
formed with whitish grey centre and
dark brown margin.
• These spots coalesce together and cause
quick death of leaves

6. Nodal blast/ culm bblast
• On nodes, blackish to brown lesions on
node which gradually spread to node, in
severe cases leads 100 % yield loss.

7. Neck blast/ panicle blast
• The infected neck region of the panicle
show dark brown to black spots and
shriveled.
• The affected plants develop chaffy grains/
light weight grains. The fungus infects the
grain also and the infected grains become
dark brown.

8. Mode of spread
• The secondary spread of the disease is through air borne.
Survival
• The pathogen survives as dormant mycelium and conidia in the
infected straw and seeds. Also, collateral hosts like Panicum
repens, Leersia hexandra, Echinochloa crusgali also harbour
the pathogen
Epidemiology
• Intermittent drizzles, cloudy weather, high RH (above 92 per
cent), low temperature

9. Management
• Suceptible varieties are mansuli, jumli
• Seed treatment with [Captan / thiram /carbendazim @ 2g / kg (or) P.fluorescens @
10g / kg of seed]. Seedling root dipping can also be followed with P.fluorescens.
• Avoid closer spacing of seedlings in the main field and excess dose of nitrogenous
fertilizers.
• Grow resistant varieties like CR 1009, Co 43 & 44, ADT 36, ADT 39 and 40.
• Spray with Pseudomonas fluorescens @ 2% or Iprobenphos @ 500 ml/ha or
Tricyclazole @ 400g/ ha can be followed.

10. • Fungi produces two toxins - α-Picolinic acid, Pyricularin
• Fungus produce pyriform conidia (2 septate and 3 celled)

11. 2. Brown leaf spot - Helminthosporium
oryzae/ Bipolaris oryzae
Symptoms
• Numerous brown, round to oval spots
(sesame shaped sports) appear on the leaves
and leaf sheaths.
• The spots appear like sesame and hence the
name sesame leaf spot. The grains also
become infected and dark brown spots can be
seen on the glumes.
• The disease is responsible for the Bengal
famine of 1942-43.

12. Mode of spread
• The primary spread is through infected seeds and the
secondary spread is through air borne conidia
Epidemiology
• 28-300C with RH 90 – 92 %

13. Management
• Use disease free seeds.
• Seed treatment either with chemicals viz., Captan / thiram /carbendazim @ 2g / kg (or)
bio control agent P. fluorescens @ 10g / kg of seed.
• Grow resistant varieties [Co 44, Bhavani]
• Spray the crop with Carbendazim @ 250 gm/ha or Mancozeb 1 kg/ha.

14. 3. Sheath blight - Rhizoctonia solani
Symptoms
• The fungus affects the crop from
tillering to heading stage.
• On the leaf sheath oval or elliptical
or irregular greenish grey spots are
formed.
• As the spots enlarge, the centre
becomes greyish white with an
irregular blackish brown or purple
brown border.
• In the advanced stages brown colour
sclerotia (Irregular shaped) are
formed in the infected tissues.

15. Mode of spread
• The pathogen spreads through irrigation water
Survival
• The pathogen can survive as sclerotia and mycelium

16. Management
• Avoid flow of irrigation water from infected to healthy fields.
• Summer ploughing helps to reduce soil borne sclerotia.
• Avoid excess dose of nitrogenous fertilizers.
• Spray with Carbendazim @ 250g / ha or chlorothalonil @ 1kg / ha or Propiconazole
@ 0.1 % during tillering stage can be followed

17. 4. Sheath rot - Sarocladium oryzae
Symptoms
• The disease affects the boot leaf covering the
panicle.
• The affected areas shows grayish brown,
oblong lesions on the upper most leaf sheath
with a grey centre and brown margins.
• In severe conditions the whitish mycelial
growth can be observed in the panicle inside
the sheath.
• The young panicles if affected remain inside
the sheath or emerge partially.

18. Survival and Mode of spread
• The pathogen survives in the infested seeds
and spreads through air borne conidia.
• The infected seeds also spread the disease

19. Management
• Avoid excess dose of nitrogen fertilizers.
• Adopt optimum spacing.
• Spray with carbendazim @ 250g/ha or mancozeb @ 1kg / ha or chlorothalonil @ 1kg
/ ha or NSKE (5%), or Ipomoea/Prosophis leaf powder extract at booting stage
controls the disease.

20. Write differences between Sheath rot and Sheath
blight diseases
Sl.no Sheath rot disease Sheath blight disease
1 Caused by Sarocladium oryzae and its
perfect stage is Acrocylindricum oryzae
Caused by Rhizoctonia solani and its
perfect stage is Thanetophorus curcumeris
2 The disease affects the boot leaf covering
the panicle or the upper most leaf sheath
Affects the crop at the collar region or the
base of the plants at the water surface
3 The fungus produces conidia The fungus produces sclerotia
4 The fungus spreads through air borne
conidia and pathogen is also seed borne
The pathogen is soil borne and spreads
through irrigation water
5 The disease is severe during boot leaf
stage
The disease is severe during maximum
tillering stage
6 The pathogen survives in the infected
plant debris
The pathogen survives as sclerotia in soil

21. 5. Stem rot - Sclerotium oryzae
Symptoms
• Small, black, irregular lesions appear on the outer leaf sheath.
• Theses spots enlarge and reach the inner leaf sheath.
• Finally the infected leaf sheath rots and sclerotia are formed in the host tissues.

22. Mode of spread
• The pathogen spreads through irrigation water.
Survival
• The pathogen survives as soil borne sclerotia in the infected stubbles and straw

23. Management
• Summer ploughing and burning the stubbles left in the infested fields.
• Balanced fertilizer application.
• Avoid flow of irrigation water from infected field to healthy field.

24. 6. Foot rot or Bakanae disease – Fusarium
moniliforme / Gibberella fujikuroi
Symptoms
• Infected plants several inches taller than normal plants
in seedbed and field
• Thin plants with yellowish green leaves and pale green
flag leaves
• Reduced tillering and drying leaves at late infection
• Partially filled grains, sterile or empty grains for
surviving plant at maturity
• In the seedbed, infected seedlings with lesions on roots
will die, which may die before or after transplanting.

25. Management
• Seed treatment with captan or carbendazim or thiram @ 2g / kg of seed.
• Seed treatment using fungicides such as thiram or thiophanate-methyl or benomyl
is effective before planting or Benomyl at 1-2% of seed weight may be used as dry
seed coating

26. 7. False smut - Ustilaginoidea virens
• It is also called as Green smut or Lakshmi disease as
the farmers believe that the lakshmi disease affected
fields normally results in a bumper harvest.
Symptoms
• The disease appears on the ears and converts individual
grains in to greenish smut balls.
• The infected ovaries are transformed in to large, velvety
green masses. Usually only few grains are affected in a
panicle.

27. Mode of spread
• The chlamydospores are air borne spores but do not
free themselves from the spore balls easily because of
the presence of the sticking material.
Survival
• The pathogens survives as sclerotia and
chlamydospores in the soil

28. Management
• Seed treatment with carbendazim 2 g/kg of seeds.
• Spraying of copper oxychloride @ 2.5 g/litre or Propiconazole @ 1.0 ml/litre at
boot leaf and milky stages will be more useful to prevent the fungal infection.
• At tillering and preflowering stages, spray Hexaconazole @ 1ml/lit or
Chlorothalonil 2g/lit.

29. 8. Udbatta disease - Ephelis oryzae
Symptoms
• The affected panicle emerges from the leaf
sheath as a slender dirty grey coloured,
cylindrical spike, rod like hard structures.
• They very much resemble as ‘’udbatta’’ hence
the name is given as udbatta disease.
• No grains are formed in the affected panicles

30. Mode of spread and Survival
• The pathogen is externally seed borne and
survives in the infested seeds.
Epidemiology
• A soil temperature of around 280 C and
abundant soil moisture favour the disease.

31. Management
• Use disease free seeds for sowing.
• Seed treatment with Captan or Thiram.
• Hot water treatment of the seeds at 50-540 C for 10 minutes before sowing gives
effective control of the disease.
• Solar treatment of seeds is effective in killing the pathogen carried in the seeds, if
any

32. 9. Grain discolouration –Fungal complex
disease
Symptoms
• Dark brown to black spots appear on the grains. The
infection may be external / internal causing
discolouration [Red, yellow, orange, pink] of the glumes /
kernels or both.
• Many fungi are found involved in the disease depending
on the locality.

33. Management
• Spray the crop at boot leaf stage with mancozeb 1kg/ha or captofal 250 g/ha or
Carbendazim 250 g/ha.
• Store the grain with less than 11 % moisture content.

34. 10. Bacterial leaf blight - Xanthomonas oryzae
pv. oryzae
Symptoms
i. Leaf blight phase
• Small water soaked streaks appear at the margin of the
lamina near the tip which enlarges and become as
straw coloured necrotic patch.
• The inner portion of the diseased leaves also shows
wavy margin.
• Under humid condition, creamy white bacterial ooze
characteristics of the disease can also be observed.
ii. ‘‘kresek’’ or wilt phase
• Destructive phage with wilting and yellowing of seedlings.
No tillering occurs, leaves and wilting hanged
downwards.
iii. Yellow leaf phase
• The affected plants show pale yellow discolouration. The
youngest leaf in a hill may turn yellow or white.

35. Management
• Avoid clipping of tip of the seedling at the time of transplanting.
• Use optimum dose of fertilizers.
• Hot water treatment of seeds for 10 minutes at 52 – 540 C
• Grow resistant varieties like IR-20, IR-36, TKM-6
• Spray streptomycin sulphate and tetracycline combination @ 300g + copper oxy
chloride @ 1.25kg/ha

36. OOZE OUT TEST
• When affected leaves are cut and immersed in clear water in a test tube, a
characteristic turbid ooze of the bacterium streaming from the vascular bundles
can be observed.

37. 11. Bacterial leaf streak - Xanthomonas
oryzae pv. oryzicola
Symptoms
• The infected leaves shows fine translucent streaks
on the veins and the lesions enlarge lengthwise and
turn brown.
• Bacterial exudates appear on the lesions at high
humidity which later dry and remain on the lesions
as particles.

38. Management
• Seed soaking with 0.25% streptocycline and hot water treatment at 520 C for 10
min.
• Spray with Agrimycin @ 100 ppm or streptocycline @100 ppm twice at 10 days
intervals.

39. 12. Tungro - Rice tungro virus [RTV]
Symptoms
• The infected plants show yellow to
orange discolouration of leaves and
rusty blotches spreading downwards
from the leaf tip.
• The infected plants become stunted.
• The infected plants produce few
spikelets and panicles are small with
discoloured grains.

40. Vector
• The disease is spread through green leaf hopper Nephotettix
virescens and N. nigropictus in a non-persistent manner
Management
• Summer ploughing and burning diseased plants (Rogueing and Field sanitation).
• Control insect vectors by spraying systemic insecticide (Monocrotophos 0.25 %)
• Growing disease tolerant varieties like CO-45, IR-50.

41. Iodine test to identify RTV
Composition of iodine solution
• [Iodine – 2g, Potassium Iodide – 6g, Water – 100 ml]
• Dilute 10 ml of the commercial tincture iodine solution available in the medical
shops with 150 ml of water

42. 13. Grassy stunt - Rice grassy stunt virus
Symptoms
• Infected plants are stunted and produce
excess tillers and have erect growth habit.
• Leaves are short, narrow, pale green / pale
yellow and have numerous rusty brown spots
of various shapes.

43. Vector
• The disease is spread by brown plant hopper (Nilaparvata
lugens) in a persistent manner.
Management
• Rogueing and Field sanitation
• Use systemic insecticides to control the vector
• Grow resistant varieties like IR-28, IR-29, IR-30, IR-32, IR-34.

44. 14. Rice Dwarf - Rice dwarf virus
Symptoms
• The infected plants show marked stunted growth with
chlorotic or whitish specks on the leaves. The number of
tillers may be reduced with retarded root growth

45. Vector
• Leaf hopper Nephotettix nigropictus and Recilia dorsalis.
• Also weeds like Echinochloa crusgalli harbour the pathogen during
off-seasons.
Management
• Rogueing and Field sanitation to destroy the weed host.
• Spraying with monocrotophos 500 ml / ha to control the insect vector.

46. 15. Yellow dwarf - Phytoplasma disease
Symptoms
• The infected plants are stunted and
have yellowish green to whitish
green leaves with excessive
tillering and leaves become soft and
droop slightly. The affected plants
are usually sterile.

47. Vector
• Green leaf hopper Nephotettix virescens and N. nigropictus
transmit the disease
Management
• Deep ploughing in summer and burning the stubbles.
• Grow resistant varieties like IR 62, IR 64.
• Control of insect vectors with systemic insecticides

49. 15. Rice Khaira
Symptoms
• Initially older
• Interveinal chlorosis
• Whitish to yellowish specks present
• mostly observed in seedling stage (2-3 weeks after transplanting)

50. Management
• Application of ZnSO4 @ 20-25 kg/ ha before transplanting.
• Root dipping @ 2 % ZNO for 1-2 minutes.
• If pH is 8-9, there is no effect of ZnSO4

51. Questions …..
ARS/ NET