A) Black or Stem Rust (Puccinia graminis tritici)

Symptoms

• Long, narrow, reddish-brown pustules (uredia) on stems, leaf sheaths, and leaves.
• Pustules run parallel to the long axis of affected plant parts.
• Uredospores give a powdery, red appearance; later, teliospores form black pustules.
• Severe infection weakens the plant, leading to lodging and yield loss.

Etiology

• Causal organism: Puccinia graminis tritici (a basidiomycete fungus).
• Spores involved: Uredospores (red, asexual), Teliospores (black, sexual), and Basidiospores.
• Alternate host: Barberry (Berberis spp.), which allows the fungus to complete its life cycle.

Disease Cycle

• Primary infection: Uredospores from infected plants are carried by wind to new wheat fields.
• Secondary infection: Uredospores spread from plant to plant.
• Teliospores: Overwinter in soil and crop debris, germinating in the next season.
• Basidiospores: Infect alternate hosts (barberry), forming pycnia and aecia, which later produce uredospores.

Management

• Eradicate self-sown wheat and weed hosts.
• Avoid planting wheat near barberry plants.
• Use resistant wheat varieties: Kalyanasona, Sonalika, Choti Lerma, Lerma Rojo.
• Seed treatment: Plantavax @ 0.1%.
• Fungicide spray: Plantavax @ 0.1%, applied 2-3 times at 15-day intervals.

B) Brown or Leaf Rust (Puccinia recondita)

Symptoms

• Small, round, orange-brown pustules on leaves.
• Pustules are irregularly scattered and turn brown as they mature.
• Teliospores appear late in the season as black, oval to linear structures covered by the epidermis.
• Reduces photosynthesis, leading to lower grain quality.

Etiology

• Causal organism: Puccinia recondita.
• Spores involved: Uredospores (orange-brown), Teliospores (black).
• No known alternate host is required to complete its life cycle.

Disease Cycle

• Primary infection: Uredospores from infected plants are carried by wind to new wheat fields.
• Secondary infection: Uredospores spread from plant to plant through wind.
• Teliospores: Overwinter in plant debris and germinate in the next growing season.

Management

• Grow resistant varieties: Lerma Rojo, Safed Lerma, Sonalika, Choti Lerma.
• Destroy weed hosts to reduce spore spread.
• Fungicide spray: Plantavax @ 0.1%.

C) Yellow or Stripe Rust (Puccinia striformis)

Symptoms

• Bright yellow pustules (uredia) appear on leaves.
• Pustules are arranged in linear rows between leaf veins (striped appearance).
• In severe infections, pustules may appear on leaf sheaths and stems.
• Late in the season, black teliospores appear in rows.
• Leads to leaf drying, poor grain filling, and yield loss.

Etiology

• Causal organism: Puccinia striformis.
• Spores involved: Uredospores (yellow), Teliospores (black).
• Alternate host: Some grass species, but not essential for the life cycle.

Disease Cycle

• Primary infection: Uredospores carried by wind infect wheat plants.
• Secondary infection: Windborne uredospores spread the disease.
• Teliospores: Overwinter in wheat debris, releasing new spores in the next season.

Favorable Conditions

• Temperature: 8-13°C is ideal for disease development.
• Humidity: High humidity and heavy rainfall favor infection.
• No infection occurs above 23°C or below 2°C.

Management

• Grow resistant varieties: Lerma Rojo, Safed Lerma, Sonalika, Choti Lerma.
• Destroy weed hosts to prevent overwintering of spores.
• Fungicide spray: Plantavax @ 0.1%.

Comparison of the Three Rust Diseases of Wheat

D) Loose Smut of Wheat (Ustilago nuda tritici)

Causal Organism

• Pathogen: Ustilago nuda tritici
• Sub-division: Basidiomycotina

Symptoms

• Symptoms appear during the emergence of ears from the boot leaf.
• All spikelets in an ear are transformed into black powdery masses of spores.
• Infected ears emerge earlier than healthy ones.

Disease Cycle

• Primary Infection: Internally and externally seed-borne. Fungus is carried as dormant mycelium within the seed, leading to systemic infection.
• Secondary Infection: Occurs through wind-borne smut spores.

Favourable Conditions Temperature of 20-21°C and high relative humidity (60-80%) during the flowering stage. Loose spikelets are more susceptible than compact spikelets.

Management

• Resistant Varieties: Kalyanasona, PV 18, WG 307, HD 450.
• Solar Seed Treatment (Luthra and Sattar, 1934): Soak seeds in water for 4 hours (8 AM to 12 Noon). Expose seeds to hot sun for 4-5 hours (12 Noon to 5 PM) on a cement or rocky surface.
• Chemical Seed Treatment: Carboxin + Thiram (Vitavax power) @ 0.2%.

E) Kernel Bunt of Wheat (Neovossia indica)

Causal Organism: Pathogen: Neovossia indica Sub-division: Basidiomycotina

Symptoms

• Affects a few grains in the spike, causing irregular arrangement.
• In severe cases, grains are reduced to black shiny sacs of teliospores.
• Outer glumes spread and inner glumes expand, exposing the bunted grains.
• Bunt balls are initially enclosed by the pericarp but burst to expose masses of spores.
• Infected plants emit a foul smell due to Trimethyl amine.

Disease Cycle

• Primary Infection: Secondary sporidia produced from primary sporidia cause primary infection.
• Secondary Infection: Occurs through wind-borne secondary sporidia.

Favourable Conditions

• Moderate temperatures (19-23°C).
• High humidity (>70%) and cloudiness or rainfall during anthesis.

Management

• Tolerant Varieties: WL 1562, HD 2281.
• Quarantine Measures: Use disease-free seed for sowing.
• Nutrient Management: Judicious application of nitrogenous fertilizers.
• Cultural Practices:
  • Adjust date of sowing to avoid favourable conditions.
  • Intercropping with Gram or Lentil to reduce disease spread

F) Powdery Mildew of Wheat (Erysiphe graminis var. tritici)

Causal Organism

• Pathogen: Erysiphe graminis var. tritici
• Sub-division: Ascomycotina

Symptoms

• Grayish white powdery growth appears on the leaf surface, leaf sheath, stem, and floral parts.
• The powdery mass consists of conidia (asexual spores) of the fungus.
• As the disease progresses, the powdery growth becomes dirty gray and later turns into black lesions due to the formation of cleistothecia (sexual fruiting bodies).
• Infected leaves curl, turn yellow, and die prematurely, leading to reduced photosynthesis.
• Severe infection can cause poor grain filling and reduced yield.

Disease Cycle

• Primary Infection: Ascospores from cleistothecia present on plant debris cause the initial infection.
• Secondary Infection: Airborne conidia spread the disease rapidly under favorable conditions.

Favourable Conditions

• Temperature: 20-21°C is ideal for the development of powdery mildew.
• High humidity (without free water on the surface) favors spore germination and infection.
• Dense planting and high nitrogen fertilization enhance susceptibility.

Management

• Cultural Practices:
  • Grow resistant varieties like C591, E750, UP1109, and VL421.
  • Avoid dense planting to ensure good air circulation.
  • Balanced fertilization to prevent excessive vegetative growth.
• Chemical Control:
  • Dust Sulphur @ 40 kg/ha.
  • Foliar spray with Callixin or Karathane @ 0.1%.
• Integrated Disease Management (IDM):

G) Alternaria Leaf Blight of Wheat (Alternaria triticina)

Causal Organism

• Pathogen: Alternaria triticina
• Sub-division: Deuteromycotina

Symptoms

• Reddish brown oval spots with bright yellow margins on young seedlings.
• Several spots coalesce in severe cases, causing drying of leaves.
• Young leaves are generally not infected.
• Heavily infected fields exhibit a burnt appearance from a distance.

Disease Cycle

• Primary Infection: Externally and internally seed-borne conidia cause primary infection.
• Secondary Infection: Spread mainly through wind-borne conidia.

Favourable Conditions Temperature of 25°C and high relative humidity favour disease development.

Management

• Seed Treatment: Soak seeds in water for 4 hours, followed by a 10-minute dip in hot water at 52°C.
• Resistant Varieties: Co.25, Sonalika, Arnautka, E6160, K7340.
• Chemical Control: Spray Mancozeb @ 0.25% or Zineb @ 0.25%.

H) Ear Cockle of Wheat (Anguina tritici)

Causal Organism

• Pathogen: Anguina tritici (a nematode)
• Group: Nematoda

Symptoms

• Malformed and twisted spikelets that give an appearance of a cockle.
• Grains are replaced by small, dark brown galls (also known as cockles).
• Affected spikes are shorter and compact compared to healthy spikes.
• Galls contain nematode larvae that are released into the soil when they come in contact with moisture.
• Infected plants often exhibit stunted growth and reduced grain yield.

Disease Cycle

• Primary Infection: Nematode larvae from galls enter the soil and infect wheat seedlings.
• Secondary Infection: Occurs when infected seeds (galls) are sown in the next season, continuing the life cycle.

Favourable Conditions Cool and moist conditions during the sowing season favour the development of the disease.

Management

• Cultural Practices:
  • Use disease-free seeds to prevent the introduction of nematodes.
  • Crop rotation with non-host crops (like legumes) to reduce nematode population.
  • Deep ploughing to bury galls and expose them to sunlight, which kills the larvae.
• Seed Treatment: Hot water treatment: Soak seeds in hot water at 54°C for 10-15 minutes to kill the nematodes inside the galls.
• Resistant Varieties: Grow resistant wheat varieties if available in the region.