Diseases of wheat: Fungal, bacterial and viral pathogens

Dr. Shivam Singh
Assistant Professor
Department of Plant Pathology
School of Agriculture, LPU
Diseases of wheat

Fungal diseases
1. Yellow rust: Puccinia striiformis
2. Brown rust: Puccinia recondita
3. Black rust: Puccinia graminis tritici
4. Loose smut: Ustilago nuda tritici
5. Common bunt: Tilletia tritici and Tilletia laevis
6. Karnal bunt: Tilletia indica
7. Powdery mildew: Erysiphe graminis
8. Flag smut: Urocystis tritici
9. Foot rot: Pythium graminicolum
10. Leaf blight: Alternaria triticina

Bacterial disease
1. Bacterial leaf streak and black chaff:
Xanthomonas campestris pv. undulosum
Viral disease
1. Barley yellow dwarf: Barley Yellow Dwarf Virus
(BYDV)
2. Barley yellow streak mosaic: Barley Yellow Streak
Mosaic Virus (BYSMV)
3. Barley yellow striate mosaic: Barley Yellow Striate
Mosaic Virus (BYSMV)

Symptoms
• The pustules contain yellow to orange-yellow
urediospores, usually form narrow stripes on the
leaves.
• The teliospores are also arranged in long stripes and
are dull black in colour.
• Pustules also can be found on leaf sheaths, necks, and
glumes.
1. Yellow rust or Stripe rust
Causal organism: Puccinia striiformis
It is heteroecious rust but
the alternate host is still unknown.

Pathogen
• Uredospores are yellow,
spherical to oval,
measuring 23-35 × 20-35
µ, with a hyaline,
minutely echinulate
spore wall with 6-16
germ pores.
• Teleutospores are dark
brown, two celled, thick
walled flattened at the
top and measure 35-63 ×
12-30 µ.
Uredospores
Teleutospores (Teliospores)

Survival and spread
• The inoculum survives in the form of uredospores
/teliospores in the northern hills during off season
on self sown crop or volunteer hosts.
• Spread occur through uredospores from hills.
Favourable conditions
• Temperature (10-20°C)
• High humidity (>80%)

Symptoms
• The pustules are circular or slightly elliptical, smaller
than those of stem rust, usually do not coalesce, and
contain masses of orange to orange-brown
Urediospores.
• Mainly found on the upper surfaces of leaves and
leaf sheaths and occasionally on the neck and awns.
2. Leaf or Brown or Orange Rust
Causal organism: Puccinia recondita
It is heteroecious rust and
the alternate host is Meadow-rue (Thalictrum sp.)

Pathogen
• Uredospores are brown,
spherical, minutely
echinulate, measuring
20-35 µ in diameter and
bearing 7-10 germ
pores.
• Teleutospores are two
celled, smooth, oblong,
thick walled and brown
with a rounded apex and
measure 35-56 × 12-23
µ.
Uredospores

Survival and spread
on self sown crop (stubbles) or volunteer hosts.
• Temperature (20-25°C) with free moisture (rain or
dew).

Symptoms
• Pustules are dark reddish brown in colour, occur
on both sides of the leaves, on the stems and on the
spikes.
• Pustules are usually separate and scattered, and in
heavy infections they coalesce.
• Prior to pustule formation, "flecks" may appear.
3. Stem or Black Rust
Causal organism: Puccinia graminis tritici
It is heteroecious rust and
the alternate host is Barberry (Berberis sp.)

• Before the spore masses break through the epidermis,
the infection sites feel rough to the touch and gives a
ragged and torn appearance.
Pathogen
• Uredospores are brown, oval shaped, thick
walled, borne singly on stalks, measure 25-35 ×
17-20 µ and bearing 4 germ pores.
• Teleutospores are dark or chestnut brown, two
celled, smooth and thick walled with a rounded
apex and measure about 40-46 × 15-20 µ.

Uredospores
Pathogen

Survival and spread
on self sown crop (stubbles) or volunteer hosts.
• Temperature (20°C)
• Moisture (>70-80%).

Management
• Mixed cropping and crop rotation.
• Avoid excess dose of Nitrogen.
• Sulphur dusting @ 35-40 kg/ha
• Spray Mancozeb @ 2g/lit or Zineb @2.5 kg/ha or
Propiconazole @ 0.1 %.
• Grow resistant varieties like PBW 343, PBW 550,
PBW 17, Lerma Rojo, Safed Lerma, Sonalika and
Chotil.
• Spray of 1 litre butter milk + 1 litre cow urine along
with 8 litres of water.

Symptoms
• The entire inflorescence is commonly affected,
except rachis, and appears as a mass of olive-black
spores, initially covered by a thin grey membrane.
• Once the membrane ruptures, the head appears
powdery.
• The powdery mass of spores is blown off by wind,
leaving behind only the central rachis.
4. Loose Smut
Causal organism: Ustilago nuda tritici
This is internally seed borne disease.

Pathogen
• The smut spores are very minute, pale,
olive-brown, spherical to oval in shape,
measure about 5-9 µ in diameter and are
adorned with minute echinulations on the
wall.
• They germinate readily in water, each spore
producing 1 four-celled germ tube
(promycelium).

Survival and spread
• The disease is internally seed borne, where
pathogen infects the embryo in the seed.
• Primary infection occurs by sowing infected
seeds.
• Infection is favoured by cool and humid
conditions during flowering period of the host
plant.

Management
• Solar heat treatment or hot water treatment of seed.
• Rogue out diseased ear heads and destroy them by
burning.
• Grow resistant varieties like Raj 2296, K-8027, K-
8251, HW-657, HW-240, Raj-6276, VL-646, VL-719
etc.
• Treat the seed with Vitavax @ 2g/kg seed before
sowing.

Symptoms
• The fungus attacks seedling of 8-10 days old and become
systemic and grows along the tip of shoot.
• At the time of flowering, hyphae concentrate in the
inflorescence and spikelets and transforming the ovary
into smut sorus of dark green colour.
• The diseased plants mature earlier and all the spikelets
are affected.
5. Common Bunt or Hill Bunt or Stinking Smut
Causal organism: Tilletia tritici (syn. T. caries)
and Tilletia laevis (syn. T. foetida)
This is externally seed borne disease.

Pathogen
• Reticulate, globose and rough walled.
• No resting period.
• Germinate to produce primary sporidia.

Survival and spread
• The spores on the seed surface germinate along with
the seed.
• Each produces a short fungal thread terminating in a
cluster of elongated cells.
• These then produce secondary spores which infect the
coleoptiles of the young seedlings before the
emergence of the first true leaves.
• In India, disease occurs only in Northern hills, where
wheat is grown.
• Temperature of 18-20˚C.
• High soil moisture.

Management
• Adopt shallow sowing.
• Grow the crop during high temperature period.
• Treat the seeds with carboxin or carbendazim at
2g/kg.
• Grow resistant varieties like Kalyan Sona,
S227, PV18, HD2021, HD4513 and HD4519.

Symptoms
• In an infected plant, not all the ears are affected and in an
infected ear, only a few grain (5-6) are being infected and
changed into sori.
• The sori are always irregularly distributed on the
infected ear.
• On the maturity of the grains, the outer glumes in a
spike spread out and the bunted grains may be observed.
6. Karnal Bunt
Causal organism: Tilletia indica
(syn. Neovossia indica)
This disease was first reported from Karnal (Haryana).

Survival and spread
• The disease is seed borne and sowing of
infected seeds is the source of primary infection.
• Temperature of 18-20˚C.
• High soil moisture.

7. Powdery Mildew
Causal organism: Erysiphe graminis
Symptoms
• Greyish white powdery
growth appears on the leaf,
sheath, stem and floral
parts.
• Powdery growth later
become black lesion and
cause drying of leaves and
other parts.

Pathogen
• Fungus produces septate, superficial,
hyaline mycelium on leaf surface with
short conidiophores.
• The conidia are elliptical, hyaline, single
celled, thin walled and produced in chains.
• Dark globose cleistothecia containing 9-30
asci develop with oblong, hyaline and thin
walled ascospores.

Survival and spread
• Fungus remains in infected plant debris as dormant
mycelium and asci.
• Primary spread is by the ascospores and secondary
spread through airborne conidia.
• Cool and moderate temperature (20-21˚C).
• High humidity (>70%).

Management
• Crop rotation
• Removal of plant debris.
• Avoid excess dose of Nitrogen.
• Use of resistant varieties.
• Spray wettable sulphur 0.2% or carbendazim
@ 500 g/ha.

8. Flag Smut
Causal organism: Urocystis tritici or U. agropyri
Symptoms
• The symptoms can be seen on stem, clum and leaves
from late seedling stage to maturity.
• The seedling infection leads to twisting and drooping
of leaves followed by withering.
• Grey to grayish black sori occurs on leaf blade and
sheath.
• The sorus contains black powdery mass of spores.

Pathogen
Aggregated spore balls, consisting 1-6 bright
globose, brown smooth walled spores
surrounded by a layer of flat sterile cells.

Survival and spread
• The disease is seed and soil borne.
• Smut spores are viable for more than 10 years.
• Primary infection occurs by sowing infected seeds
or by resting spores present in the soil.
• Temperature of 18-24°C.
• Relative humidity (65% and above).

Management
• Crop rotation
• Seed treatment with carboxin at 2g /kg.
• Grow resistant varieties like Pusa 44 and WG
377.

9. Foot rot
Causal organism: Pythium graminicolum / P.
arrhenomanes
Symptoms
• The disease mainly
occurs in seedlings &
roots and rootlets
become brown in colour.
• Seedlings become pale
green and have stunted
growth.

Pathogen
• Mycelium is well developed and coenocytic,.
• Fungus produces sporangia and zoospores.
• The sexual spores are the oospores, borne singly which
are moderately thick walled.
Disease Cycle

Survival and spread
• Pathogen survives in soil.
• Primary spread occurs through soil and irrigation
water.
• Wet weather and high rainfall.
Management
• Follow crop rotation
• Seed treatment with carboxin or carbendazim @2 g
/kg.

10. Leaf Blight
Causal organism: Alternaria triticina, A. alternata
and Bipolaris sorokiniana
Symptoms
• Reddish brown oval spots
appear on young seedlings
with bright yellow
margin.
• In severe condition,
several spots coalesce to
cause drying of leaves.

Survival and spread
• Primary spread is by externally seed-borne and soil
borne conidia.
• Secondary spread by air-borne conidia.
• Temperature of 25°C.
• Relative humidity (>70%).
Management
• Seed treatment with carboxin or carbendazim @2 g
/kg.
• Spray with Mancozeb or Zineb @2 kg/ha.

11. Bacterial leaf streak and black chaff
Causal organism: Xanthomonas campestris pv. undulosum
or
Xanthomonas translucens pv. undulosa
Symptoms
• Initially, small and linear water soaked area may develop
on the leaf blades and sheath.
• Later, lesions elongate and coalesce into irregular, narrow
yellowish and brownish stripes.
• Spikes are blighted and turn black.
• Cream to yellow coloured slime or droplets appear on
the leaves.

Pathogen
• Xanthomonas is a genus of Proteobacteria and is a
Gram negative.
• It is motile by a single polar flagellum and it can
grow in temperature range from 4ºC to 37ºC.
Survival and spread
• The bacterium survives in and on seeds and may also
persist on crop residue and in soil.
• It can be transmitted by splashing water, plant to
plant contact and insects.
• Volunteer and grassy weeds also are sources of
inoculums.

• Wet weather, irrigation water and rainfall.
• Temperature of 25-30ºC.
Management
• Crop rotation.
• Bury infected plant parts.
• Removal of volunteer and grassy weeds.
• Avoid overirrigation.
• Use of disease free seed.
• Use of resistant cultivars like Blade, Cromwell, Faller,
Howard, Knudson etc.

12. Barley yellow dwarf
Causal organism: Barley Yellow Dwarf Virus (BYDV)
Symptoms
• The most common symptom is stunting due to reduced
internode length and root mass of infected plants is also
often reduced.
• The most conspicuous symptom is loss of green colour in
leaves, mostly found on older leaves and later water-
soaked areas are found on the leaves.
• Leaves typically turn yellow or red or purple in colour.
• Other symptoms include upright and stiff leaves and
serrated leaf borders, reduced tillering and flowering,
sterility and failure to fill kernels.

Pathogen
• This virus is typically 25-28 nm in diameter and
hexagonal in outline.
• It has ssRNA (single-stranded ribonucleic acid)
genome.
Transmitted by Aphids (Sitobion avenae and
Rhopalosiphum padi).
• High light intensity and relatively cool temperatures
(15-18ºC)

Management
• Late sowing.
• Removal of volunteer plants and grassy weeds.
• Use of disease free seed.
• Use of resistant varieties.
• Use of Imidacloprid or Thiamethoxam.

Diseases of wheat: Fungal, bacterial and viral pathogens

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