A) Downy Mildew / Green Ear of Pearl Millet

Causal Organism: Sclerospora graminicola

Economic Importance

• Found in Africa and India, first reported by Butler in 1907.
• Particularly severe in ill-drained and low-lying areas.
• Yield Losses: Can reach 30-45% in high-yielding varieties.
• Notable epidemics occurred in 1970 and 1983, affecting popular hybrids HB 3 and BJ 104.

Symptoms

• Systemic infection affecting both leaves and earheads.
• Early Symptoms:
  • Appear at the three to four leaf stage in seedlings.
  • Light green to light yellow patches on the upper leaf surface.
  • White downy growth on the corresponding lower surface, composed of sporangiophores and sporangia.
  • Yellow discoloration often develops into streaks along the veins.

• Advanced Symptoms:
  • Excessive tillering and dwarfing of plants.
  • Streaks turn brown and leaf tips shred, though less prominently than in Jowar.

• Green Ear Symptom:
  • Earheads fail to form or become malformed into twisted green leafy structures, leading to the name Green Ear Disease.
  • Floral parts (glumes, palea, stamens, and pistil) transform into green linear leafy structures.
  • These leafy structures turn brown and dry as the disease progresses, eventually bearing masses of oospores.

Pathogen

• Mycelium: Systemic, non-septate, and intercellular in parenchymatous tissues.
• Sporangiophores: Short, stout, and hyaline, arising through stomata. Irregular branching produces sterigmata bearing sporangia.
• Sporangia: Hyaline, thin-walled, and elliptical, with prominent papilla.
• Oospores: Round, surrounded by a smooth, thick, yellowish-brown wall.

Disease Cycle

• Primary Infection: Oospores remain viable in soil for five years or longer, causing primary infection in seedlings. Oospores attached to seeds also lead to primary and systemic infections.
• Secondary Spread: Through sporangia, active during the rainy season and disseminated by air and water. Secondary infections are generally localized and may not become systemic.
• Alternate Hosts: Teosinte (Euchlaena mexicana) and Foxtail Millet (Setaria italica).

Favourable Conditions

• High humidity (90%) and water on leaves.
• Low temperatures (15-25°C) favor the formation of sporangiophores and sporangia.

Management

i) Cultural Practices:

• • Select seeds from healthy crops.
  • Collect and burn diseased plants before oospore formation.
  • Summer deep ploughing to expose oospores to sunlight.
  • Rogue out infected plants promptly.
  • Prolonged crop rotation to break the disease cycle.

ii) Resistant and Tolerant Varieties:

• • Resistant Varieties: WCC 75, PHB 10, ICMH 451, ICTP 8203, Mallikarjuna, HB-1, HB 5, PHB 14.
  • Tolerant Varieties: MBH 118, CM 46, Balaji Composite, Nagarjuna Composite, Visakha Composite, New Vijaya Composite, RBS 2.

iii) Seed Treatment: Metalaxyl (Apron 35 SD) @ 6 g/kg of seed. Thiram or Captan @ 4 g/kg of seed.

iv)  Chemical Control: Spray Mancozeb @ 0.25% or Metalaxyl (Ridomil MZ) @ 0.2%.

• • Timing of Sprays: 30 days after sowing. Repeated sprays at 15-day intervals, especially during rainy periods.

B) Ergot or Sugary Disease of Bajra

Causal Organism: Claviceps fusiformis or C. microcephala

Economic Importance

• The disease became an epidemic in 1967-78 on newly introduced hybrid Bajra varieties.
• It significantly affected hybrids HB-1 and HB-2, leading to 25% yield losses in Bagalkot, Belgaum, and Bijapur areas of Karnataka.
• In severe cases, yield losses ranged from 41% to 70%.

Symptoms

• Honey Dew Exudation: Infected spikelets exude small droplets of light pinkish or brownish sticky fluid (honey dew).
• Sticky Earheads: Under severe infection, honey dew trickles along the earhead, making upper leaves sticky and attracting insects.
• Sclerotial Bodies: In later stages, the infected ovary is replaced by dark brown sclerotial bodies, larger than the seed, with pointed apexes protruding from the florets.

Pathogen Characteristics

• Mycelium: Septate and produces closely arranged conidiophores.
• Conidia: Hyaline and one-celled.
• Sclerotia:
  • Small, dark grey outside but white inside.
  • Size: 3-8 mm long and 0.3-1.5 mm broad.

Disease Cycle

• Primary Infection: Occurs through germinating sclerotia present in the soil.
• Secondary Spread: By insects, air-borne conidia, and ascospores.
• Collateral Hosts: Cenchrus ciliaris, C. setigerus, and other Pennisetum species contribute to the pathogen’s survival.

Favourable Conditions

• Susceptible Stage: Flowers are susceptible between stigma emergence and pollination.
• Weather Conditions: Overcast skies, drizzling rain, and temperatures between 20°C to 30°C during flowering favor disease development.

Management Strategies

i) Cultural Practices: Adjust sowing dates to avoid flowering during September (high rainfall and humidity). Seed Treatment: Immerse seeds in 10% common salt solution to remove floating sclerotia. Eradicate collateral hosts.

ii) Resistant Varieties: PHB 10, PHB 14, Co 2, Co 3, and Bajra 24.

iii) Chemical Control: Ziram: 0.2% spray at boot leaf and flowering stages. Carbendazim: 0.1% spray. Mancozeb: 0.2% spray.