4. What is Plant Disease ?
Any variation in normal as expressed either by the checking or by
the interruption of physiological activities or by structural changes,
which are sufficiently permanent to check the development , causes
abnormal formations or lead to premature death of a part of the plant
or the entire plant (Held, 1933)
Condition in which functions of the organisms are not properly
discharged (Ward, 1901)
8. 1. RICE BLAST
Etiology:
Anamorph =Pyricularia oryzae
Teleomorph= Magnaporthe grisea
Symptoms:
The fungus attacks the crop at all stages from seedlings in nursery
to heading in main field.
Typical symptoms appear on leaves, nodes, rachis, and glumes.
9. LEAF BLAST
It starts from lower leaves to upper
Eye spindle shaped spots appear on
leaves
Brown margins with greyish centre
Lesion enlarge, coalesce and kill the
leaves
Severely infected nursery and field
show a burnt appearance.
10. NODE BLAST
Irregular black areas
encircle the infected nodes
which may break up
leading to the death of all
plant parts above the point
of infection
11. NECK BLAST
At the flower emergence, the
fungus attacks the peduncle
which is engirdled, and the
lesion turns to brownish-black
In early neck infection, grain
filling does not occur and the
panicle remains erect like a dead
heart caused by a stem borer
In the late infection, partial
grain filling occurs
12.
13. PREDISPOSING FACTORS-RICE BLAST
Application of excessive doses of nitrogenous fertilizers
Intermittent drizzles, cloudy weather
High relative humidity (93-99%), low night temperature
(between 15-20̊C or less than 26̊C)
More number of rainy days, longer duration of dew, slow wind
movement
Availability of collateral hosts
14. DISEASE CYCLE
PSI: Mycelium and conidia in the infected straw and seeds. Panicum
repens, Digitaria marginata, Brachiaria mutica, Leersia hexandra,
serve as collateral hosts in tropics
SSI: Conidia dispersed through wind
15. MANAGEMENT
The primary control option for blast is host-plant resistance e.g. Radha-4, Radha-7,
Radha-13, Khumal-4, Khumal-13, Sukkha-1, Sukkha-6, Chandannath-1, Sabitri, etc
Split application of nitrogenous fertilizer and good water management (flooding the
soil) are recommended to manage the disease
Remove and destroy the weed hosts in the field bunds and channels
Seed treatment with biocontrol agent Trichoderma viride @ 4g/kg or Pseudomonas
fluorescens @ 10g/kg of seed
Treat the seeds with Carbendazim or Derosol @ 2-3 g/kg
Spray the main field 3 times with Tricyclazole 75%WP @0.75 gm per litre water or
Kasugamycin 3% SL @1.5 ml per litre water at an interval of 15 days
16. 2. BROWN SPOT OF RICE
Etiology:
Anamorph = Bipolaris oryzae
Teleomorph= Cochliobolus miyabeanus
Bipolaris oryzae produces brown septate
mycelium
Conidiophores arise singly or in small
groups. They are geniculate, brown in
colour.
Conidia are generally curved, boat, or club-
shaped, with 6 to 14 transverse septa or
cross walls
17. SYMPTOMS
The fungus attacks the crop
from seedling in nursery to
milky stage in main field.
Symptoms appear as oval to
circular lesions (spots) on the
coleoptile, leaf blade, leaf
sheath, and glumes, being most
prominent on the leaf blade and
glumes
Several spots on leaves
coalesce and the leaf dries up.
18. Dark brown or black spots
also appear on glume which
reduces the grain quality and
weight.
Deficiency of potassium
predisposes the plants to heavy
infection
Contd….
19. High relative humidity (86-100%), prolonged periods of leaf
moisture and high temperatures(16-36ºC) are highly favourable
for the fungi
Excess of nitrogen aggravates the disease incidence
Infected plants debris left in the field and weeds
PREDISPOSING FACTORS-BROWN SPOT
20. DISEASE CYCLE
PSI: Conidia in plant debris and seed coat. Digitaria sanguinalis, Leersia
hexandra, Echinochloa colonum, Pennisetum typhoides, Setaria italica and
Cynodon dactylon serves as collateral hosts
SSI: Wind borne conidia
21. The primary control option for brown spot is host-plant resistance e.g. CH-
13, CH-45, etc
Acquire your seeds from certified sources if possible
Field sanitation-removal of collateral hosts and infected debris in the field.
To be sure that the seeds are not contaminated, pre-soak seeds in cold water
for 8 hours, then a seed bath in hot water (53-54ºC) for 10 to 12 minutes is
recommended
Treat the seeds with Carbendazim or Derosol @2-3 g/kg
Spray the crop in the main field thrice with Mancozeb 75%WP or Propineb
70%WP @ 3gm per litre water at an interval of 15 days
MANAGEMENT
22.
23. Etiology:
Anamorph = Rhizoctinia solani
Teleomorph= Thanetophorus cucumeris
Produces usually long cells of septate
mycelium which are hyaline when
young, yellowish brown when old.
Produces large number of globose
sclerotia, which are initially white,
later turn to brown or purplish brown
3. SHEATH BLIGHT OF RICE
24. Initial lesions are small,
ellipsoidal or ovoid,
greenish-gray and water-
soaked and usually
develop near the water
line in lower leaves
SYMPTOMS
25. Older lesions are elliptical or ovoid with a grayish white
center and light brown to dark brown margin
Lesions may coalesce forming bigger lesions with irregular
outline and may cause the death of the whole leaf
Contd….
26. Severely infected plants produced poorly filled or empty grains,
especially those on the lower portion of the panicles
Brown sclerotia of the fungi are observed on the infected area of
the plant
Contd….
27. Presence of the disease in the soil
Presence of sclerotia or infection bodies floating on the water
Closer planting
Relative humidity from 96 to 100%
Temperature from 28-32 °C
High levels of nitrogen fertilizer
Presence of irrigation water
Growing of high yielding improved varieties
late tillering or early internode elongation growth stages
PREDISPOSING FACTORS-SHEATH BLIGHT
28. PSI: Sclerotia in soil
SSI: Sclerotia spread through irrigation water
DISEASE CYCLE
29. Avoid excess doses of nitrogenous fertilizers
Adopt optimum spacing
Some level of resistance varieties such as Makwanpur 1, Radha 11, Radha 12,
Sabitri, Hardinath 1 are suggested to grow
Avoid flow of irrigation water from infected fields to healthy fields
Deep ploughing in summer and burning of stubbles
Soil application of P.fluorescens @ of 2.5 kg/ha after 30 days of transplanting
(This product should be mixed with 50 kg of FYM/Sand and then applied)
Spray Propiconazole@0.1% or Pencycuron 22.9 SC @ 0.15% or Validamycin
@0.3% from 45 days after transplanting at 10-12 days interval for 2 times
depending upon the intensity of disease
MANAGEMENT
30. Etiology:
Sarocladium oryzae
The fungus produces whitish,
sparsely branched and septate
mycelium
Conidiophore is slightly thicker than
the vegetative hyphae
Conidia are hyaline, smooth, single
celled and cylindrical in shape
4. SHEATH ROT OF RICE
31. Sheath rot occurs usually at the booting
stage of the crop
Oblong or irregular greyish brown spots
appear on the flag leaf
Spots enlarge with grey centre and brown
margins covering major portions of the leaf
sheath
The affected sheath and panicles rot with
abundant whitish powdery fungal growth
inside the leaf sheath
Young panicles may remain within the
sheath or emerge partially
Infected grain discolours and shrivels
SYMPTOMS
32. Closer planting
High doses of nitrogen
High humidity and temperature around 25-30°C
Injuries made by leaf folder, brown plant hopper and mites
increase infection
PREDISPOSING FACTORS-SHEATH ROT
33. Apply recommended doses of fertilizers.
Adopt optimum spacing
Soil application of gypsum in 2 equal splits (500 kg/ha) reduce the sheath rot
incidence.
Application of Neem Seed Kernal Extract (NSKE) 5% or Ipomoea leaf powder
extract 25 Kg/ha. First spray at boot leaf stage and second 15 days later.
Spray twice with Carbendazim @0.1% or Mancozeb@0.2% or
Chlorothalonil@0.2% at boot leaf stage and 15 days later.
DISEASE CYCLE
MANAGEMENT
PSI: Externally seed borne and Infected plant debris
SSI: Wind borne conidia
34.
35. 5. FALSE SMUT OF RICE
Etiology:
Anamorph = Ustilaginoidea virens
Teleomorph= Claviceps oryzae
The causal organism is a fungus
Microscopically the chlamydospores or
the conidia of the fungus are spherical to
elliptical.
They are pale and almost smooth when
young, olivaceous and warty when
mature.
36. At early stages the spore balls
are covered by a membrane
which bursts with further growth
Individual grains are transformed
into yellow or greenish spore
balls of velvety appearance which
are small at first and 1 cm or
longer at later stages
Usually only a few spikelets in a
panicle are affected.
SYMPTOMS
37. Presence of rain and high humidity
Application of high doses of nitrogenous fertilizers at
flowering stage of crop induces high incidence of disease.
Presence of wind for dissemination of the spores from plant
to plant
Presence of overwintering fungus as sclerotia and
chlamydospores
Rainfall and cloudy weather during flowering and maturity
PREDISPOSING FACTORS-FALSE SMUT
38. PSI: Ascospores produced from overwintered sclerotia
SSI: Air borne chlamydospores which do not free easily from the
spore balls due to the presence of sticky material
DISEASE CYCLE
39. Removal and proper disposal of infected plant debris
Use of disease-free seeds that are selected from healthy crop
Seed treatment with Carbendazim 2.0g/kg of seeds
Spraying of Copper oxychloride at 2.5 g/litre or Propiconazole
at 1.0 ml/litre at panicle emergence stage will be more useful to
prevent the fungal infection
MANAGEMENT
40. Etiology:
Anamorph = Sclerotium oryzae
Teleomorph= Leptosphaeria salvinii
White to greyish hyphae, spherical
black and shiny sclerotia, visible to
naked eyes as black masses.
6. STEM ROT OF RICE
41. Small black lesions are
formed on the outer leaf
sheath near the water line
and they enlarge and reach
the inner leaf sheath also.
Affected tissues rot with
profuse mycelial growth
and abundant sclerotia in
the rotting tissues.
The culm collapses and
plants lodge.
SYMPTOMS
42. Infestation of leaf hoppers and stem borer.
High doses of nitrogenous fertilizers.
PREDISPOSING FACTORS-STEM ROT
DISEASE CYCLE
PSI: Sclerotia in plant stubbles and soil
SSI: Sclerotia through irrigation water
43. Use recommended doses of fertilizer.
Deep ploughing in summer and burning of stubbles and
infected straw
Draining off the irrigation water and allow the soil to dry
Avoid flow of irrigation water from infected fields to healthy
fields.
Use of resistant or non-lodging varieties
Chemicals based on Validamycin or Hexaconazole @ 2ml/l,
Propiconazole @ 1g/l of water twice at 15 days interval, usually
from the mid tillering stage, or at the time of disease initiation
MANAGEMENT
44. Etiology:
Anamorph = Fusarium moniliforme
Teleomorph= Gibberella fujikuroi
Fungus produces both macroconidia
and microconidia
Microconidia are hyaline, single celled
and oval
Macroconidia are slightly sickle
shaped, and two to five celled.The
fungus produces the phytotoxin ,
fusaric acid, which is non-host
specific.
7. FOOT ROT OR BAKANAE OF RICE
45. The seedlings develop into abnormally
tall plants with pale, thin and dry leaves
In the main field, the affected plants
have tall lanky tillers with longer
internodes and aerial adventitious roots
from the nodes above ground level
The root system is fibrous and bushy
The plants are killed before earhead
formation or they produce only sterile
spikelets
When the culm is split open white
mycelial growth can be seen
SYMPTOMS
46. High temperatures of 30 to 35ºC favour the development of the
disease
High nitrogen application favour the disease
PREDISPOSING FACTORS-BAKANAE
DISEASE CYCLE
PSI: Mycelium and conidia in the infected straw, soil and seeds
SSI: Conidia dispersed through wind
47. Use tolerant varieties e.g. Taichung-176, Khumal-11
Use clean seeds to minimize the occurrence of the disease
Monitor your seedlings
Avoid over fertilization with nitrogen rich fertilizers
Deep plowing of fields before planting helps to expose the soil to UV
lights
Destroy the stubbles of the previous crop by plowing before sowing
Treat the seeds with Carbendazim or Derosol @2-3 g/kg
Soaking seeds with fungicide solution containing Propiconazole for
five hours has been shown to be useful
MANAGEMENT
48. Etiology:
Anamorph = Cercospora oryzae
Teleomorph= Sphaerulina oryzae
Conidiophores are produced in
groups and brown in colour.
Conidia are hyaline or sub
hyaline, cylindrical and 3-5
septate.
8. NARROW BROWN SPOT OF RICE
49. The fungus produces short, linear
brown spots mostly on leaves and
also on sheaths, pedicels and
glumes.
The spots appear in large numbers
during later stages of crop growth.
It may also occur as long and
about 1mm narrow, short and dark
on resistant varieties, but wide and
light brown on susceptible ones.
SYMPTOMS
50. Destruction of infected plant debris.
Spray Mancozeb@0.2% or Carbendazim@0.1% twice at 15
days interval starting with disease appearance
DISEASE CYCLE
MANAGEMENT
PSI: Infected plant debris
SSI: Air borne conidia produced on leaves
52. Etiology:
Xanthomonas oryzae pv. oryzae
The bacterium is aerobic, gram
negative, non spore forming, rod
with size ranging from 1-2 x 0.8-
1.0µm with monotrichous polar
flagellum.
Bacterial colonies are circular,
convex with entire margins, whitish
yellow to straw yellow colored and
opaque.
1. BACTERIAL LEAF BLIGHT
53. The bacterium induces either wilting of plants (Kresek) in
seedling stage or leaf blight in grown up plants
In grown up plants water soaked, translucent lesions
appear usually near the leaf margin. The lesions enlarge
both in length and width with a wavy margin and turn
straw yellow within a few days, covering the entire leaf
Milky or opaque dew drops containing bacterial masses
are formed on young lesions in the early morning hours.
They dry up on the surface leaving a white encrustation
If the cut end of leaf is dipped in water, bacterial ooze
makes the water turbid
The affected grains have discoloured spots surrounded
by water soaked areas
SYMPTOMS
55. Clipping of tip of the seedling at the time of transplanting
Heavy rain, heavy dew, flooding, deep irrigation water, severe
wind
Temperature of 25-30ºC
Application of excessive nitrogen, especially late top dressing
Close planting
PREDISPOSING FACTORS-LEAF BLIGHT
56. DISEASE CYCLE
PSI: Bacteria over-wintering in seed (husk and endosperm), soil, plant stubbles
and debris
SSI: Bacteria spread through irrigation water, rain storms and typhoons
57. Destroy affected stubbles by burning or through deep ploughing
Judicious use of nitrogenous fertilizers
Avoid clipping of tip of seedling at the time of transplanting.
Avoid flooded conditions or dry the field (not at the time of flowering)
Remove and destroy weed hosts.
Use resistant varieties like Bindeswori, Sabitri, Chaite-2, Chaite-4,
Radha-4, Radha-7, Radha- 11and Radha-12 or Hardinath-1
Seed treatment with agrimycin-100 @0.25 gm per litre for 30 minutes
Spray Streptocycline (250 ppm) along with copper oxychloride (0.3%)
MANAGEMENT
58.
59. Etiology:
Xanthomonas oryzae pv. oryzicola
The bacterium is aerobic, Gram negative, Non spore forming,
Rod shaped with size ranging from 0.55-0.75×1.35-2.17µm
with monotrichous polar flagellum.
2. BACTERIAL LEAF STREAK
PREDISPOSING FACTORS-LEAF STREAK
High relative humidity (83-93%) or dew during morning hours
for 2 to 3 hours
60. Fine translucent streaks appear
between the veins of the leaf
which enlarge lengthwise and
advance over larger veins
laterally and turn brown.
Yellow halo appears around the
lesions in highly susceptible
varieties
On the surface of the lesions,
bacteria ooze out and form small
yellow bandlike exudates under
humid conditions
SYMPTOMS
61. PSI: Bacteria in the infected seed
SSI: Bacteria spread through irrigation water, rain storms and typhoons
DISEASE CYCLE
62. Destroy affected stubbles by burning or through deep ploughing
Judicious use of nitrogenous fertilizers
Avoid clipping of tip of seedling at the time of transplanting.
Avoid flooded conditions or dry the field (not at the time of flowering)
Avoid flow of irrigation water from infected to healthy field
Soak the seed in Streptocycline (250 ppm) followed by hot water
treatment at 52ºC for 30 minutes to eradicate seedling infection.
Spray Streptocycline (250 ppm) along with Copper oxychloride (0.3%)
MANAGEMENT
66. Etiology:
Rice tungro bacilliform virus (RTBV)
and Rice tungro spherical virus
(RTSV)
Two morphologically unrelated
viruses present in phloem cells. Rice
tungro bacilliform virus (RTBV)
bacilliform capsid, circular ds DNA
genome and Rice tungro spherical
virus (RTSV) isometric capsid ss
RNA genome.
1. RICE TUNGRO VIRUS
67. Infection occurs both in the nursery and in the
main field.
Plants are markedly stunted
Yellow to orange discolouration of leaves with
interveinal chlorosis
Yellowing starts from the tip of the leaf and may
extend to the lower part of the leaf blade.
Young leaves are often mottled with pale green to
whitish interveinal stripes and the old leaves may
have rusty streaks of various sizes
Infected plants have few spikelets and panicles
are small with discoloured grains
SYMPTOMS
68. Presence of the virus sources
Presence of the vector
Age and susceptibility of host plants.
Rice plants in irrigated areas are much more susceptible to develop the disease
than rainfed or upland rice
PREDISPOSING FACTORS-TUNGRO VIRUS
Tungro infected plants can be chemically identified by Iodine Test.
Cut 10 cm long rice leaf tip in the early morning before 6 A.M.
Dip the leaf tip for 30 minutes in a solution containing 2g Iodine and 6 g Potassium
Iodide in 100 ml of water
Appearance of dark blue streaks confirms the tungro disease
TEST FOR DIAGNOSIS OF TUNGRO DISEASE
69. PSI: Wild rice, stubbles of infected plants and weed hosts like Eleusine indica,
Echinochloa colonum, Echinochloa crusgalli serve as a primary source of inoculum
SSI: Viral particles dispersed through leaf hoppers Nephotettix virescens, N.
nigropictus, N. parvus, N.malayanus and Recilia dorsalis
DISEASE CYCLE
70. Crop rotation with non host crops
Eradication of tungro hosts-destroy stubbles .
Destroy the eggs and breeding sites through plowing
Adopt alternate wetting and drying the field
Make sure to conserve beneficial insects
Light traps have successfully been used to attract and control the
green leafhopper vectors as well as to monitor the population
Spraying buprofezin at 15 and 30 days after transplanting can
work if done in a timely manner
MANAGEMENT
71. 2. RICE GRASSY STUNT VIRUS
Etiology:
Rice grassy stunt tenuivirus, filamentous rod, 950-1350nm long x 6nm wide, ssRNA
genome
SYMPTOMS
Plants are markedly stunted with
excessive tillering and an erect growth
habit.
Leaves become narrow, pale green
with small rusty spots.
May produce a few small panicles
which bear dark brown unfilled grains.
72. Disease spreads by the brown plant hopper, Nilaparvata lugens, in a
persistent manner having a latent period of 5 to 28 days in the vector.
Ratoon crop and presence of vector perpetuate the disease from one
crop to other.
DISEASE CYCLE
MANAGEMENT
To control rice grassy stunt virus the brown planthopper vectors need to be
managed.
This can be done either through the use of insecticides and brown plant
hopper-resistant varieties
Infected stubble needs to be plowed under after harvest to reduce the virus
source.
73. Etiology:
Rice dwarf virus
The virus is spherical, 70nm diameter with an
envelope, dsRNA genome.
Symptoms:
Infected plants show stunted growth, reduced
tillering and root system.
Leaves show chlorotic specks turning to
streaks along the veins. In early stage of
infection no ear heads formed.
3. RICE DWARF VIRUS
74. Spreads by leafhopper feeding by Nephotettix cincticeps, Recllia
dorsalis and N. nigropictus in a persistent manner.
The transmission is transovarial through eggs.
Gramineous weeds Echinochloa crusgalli and Panicum
miliaceaum serve as source of inoculum.
DISEASE CYCLE
MANAGEMENT
Destory weed host that serve as source of inoculum
Spraying buprofezin at 15 and 30 days after transplanting can
work if done in a timely manner
77. 1. WHITE TIP
Etiology:
Aphelenchoides besseyi
Symptoms:
Leaf tips turn white with a
yellow area between healthy
and diseased tissue; white
areas sometimes occur on
leaf edges
79. MANAGEMENT
The most common management practice for A. besseyi is to
maintain clean seed stocks
Crop rotation of one to two years with non-host crop is quite
effective
Soak the seeds in water for 24 hours, later hot water
treatment at 52°C for 10 min
Apply carbofuran 3G @ 13 kg or fipronil 0.3G @ 13kg per
acre of nursery, 5 to 7 days before pulling the seedlings for
transplanting
80. 2. Ufra disease
Etiology:
Ditylenchus angustus
Symptoms:
Infested leaves become yellow-whitish
and wither, seedlings often die.
Brown spots appear on leaves and leaf
sheaths of surviving plants.
Stems may also bear spots and these
become darker brown at upper inter-
nodes of the stem.
Ears may not emerge or may show
swellings and become twisted and
distorted.
81. Apply crop rotation
Grow early maturing varieties
Use healthy seeds and plough the field thoroughly after
harvest so as to expose the soil to sun-heat
A nematicide may be applied in heavily affected fields
MANAGEMENT
82. Illustrated guide to disease symptoms on leaves
BACTERIAL
LEAF BLIGHT
Gray to brown,uneven
lesions progressing
downwards.
SHEATH BLIGHT
Large, irregular lesions with
dark brown margin and
gray center.
BROWN SPOT
Circular to oval dark brown
spots with brown margins
and light gray center.
83. BACTERIAL
LEAF STREAK
Linear, water-soaked, yellowish
streaks between the veins.
RAGGED STUNT
Leaves with ragged
edge and twisted tip.
Whitish galls on veins.
TUNGRO
Yellow to yellow orange
leaves. Young leaf is
mottled.
GRASSY STUNT
Light green, narrow,
and erect leaves with
numerous darkspots.
Illustrated guide to disease symptoms on leaves
