False smut of rice
Causative agent: Ustilaginoidea virens (Syn: Claviceps oryzae – sativa)
- Affects only panicle initiation to maturity.
Symptoms:
- Individual rice grain transformed into a mass of velvety spores or yellow fruiting bodies
- Growth of velvety spores enclose floral parts
- Immature spores slightly flattened, smooth, yellow, and covered by a membrane.
- Growth of spores result to broken membrane
- Mature spores orange and turn yellowish green or greenish black
- Only few grains in a panicle are usually infected and the rest are normal.
Etiology
Chlamydospores are formed on the spore balls, they are spherical to elliptical, waxy and olivaceous.
Favorable condition:
- High relative humidity (>90%)
- Temperature ranging from 25−35 ºC.
- Rain, high humidity, and soils with high nitrogen content also favor disease development. Wind can spread the fungal spores from plant to plant.
Survive and spread:
- Air born disease
- Survive: sclerotia and chlamydospore
- Spread: ascospore is a primary source of inoculum produced from sclerotia and chlamydospores are secondary source of inoculum which is transmitted by air.
Management:
- Remove infected seeds, panicles, and plant debris after harvest.
- Reduce humidity levels through alternate wetting and drying (AWD) rather than permanently flooding the fields
- Treat seeds at 52°C for 10 min.
- Spray copper oxychloride@0.3% or carbendazim@0.1% at panicle emergence
- At tillering and preflowering stage spray hexaconazole @1ml/l, chlorathalonile @2g/l, copper based fungicide are effective.