Flase smut: Ustilaginoidea virens
Symptoms:
- Individual rice grain transformed into a mass of yellow fruiting bodies
- Growth of velvety spores that enclose floral parts
- Infected grain has greenish smut balls with a velvety appearance.
- The smut ball appears small at first and grows gradually up to the size of 1 cm.
- It is seen in between the hulls and encloses the floral parts.
- Only a few grains in a panicle are usually infected and the rest are normal.
- As the fungi growth intensifies, the smut ball bursts and becomes orange then later yellowish-green or greenish-black in colour.
- Infection usually occurs during the reproductive and ripening stages, infecting a few grains in the panicle and leaving the rest healthy.
Conditions that favour disease development:
- Presence of rain and high humidity
- Presence of soils with high nitrogen content
- Presence of wind for dissemination of the spores from plant to plant
- Presence of overwintering fungus as sclerotia and chlamydospores
- Flowering stage of the rice crop
Identification of pathogen:
- Chlamydospore formed on the spore balls are born laterally on minute sterigmata on radial hyphae, and are spherical to elliptical, warty, olivaceous, 3-5 x 4-6 µm. Younger spores are smaller, paler, and almost smooth.
- Some of the green spore balls develop one to four sclerotia in the centre. These sclerotia overwinter in the field and produce stalked stromata the following summer or autumn.
- In temperate regions, the fungus survives the winter by means of sclerotia as well as chlamydospores.
- It is believed that the primary infections are initiated mainly by the ascospores produced from the sclerotia.
- Chlamydospores play an important role in secondary infection, which is a major part of the disease cycle.
Management: Cultural methods:
- Among the cultural control, destruction of straw and stubble from infected plants is recommended to reduce the disease.
- Use varieties that are found to be resistant or tolerant to the disease in India.
- Avoid field activities when the plants are wet.
- Early planted crop has fewer smut balls than the late planted crop.
- At the time of harvesting, diseased plants should be removed and destroyed so that sclerotia do not fall in the field. This will reduce primary inoculum for the next crop.
- Field bunds and irrigation channels should be kept clean to eliminate alternate hosts.
- Excess application of nitrogenous fertilizer should be avoided.
- Regular monitoring of disease incidence during rabi season is very essential.
- Proper Destruction of straw and stubble.
Preventive methods:
- Use of disease-free seeds that are selected from the healthy crop.
- Split application of nitrogen is recommended.
- Removal and proper disposal of infected plant debris.
Chemical methods:
- Seed treatment with carbendazim 2.0g/kg of seeds.
- Spraying of copper oxychloride @ 2.5 g/litre or Propiconazole @ 1.0 ml/litre at boot leaf and milky stages will be more useful to prevent the fungal infection.
- At tillering and pre-flowering stages, spray Hexaconazole @ 1ml/lit or Chlorothalonil 2g/lit.
- In areas where the disease may cause yield loss, applying captan or captafol or fentin hydroxide or mancozeb can inhibit conidial germination.
- At tillering and pre-flowering stages, spraying of carbendazim fungicide or copper base fungicide can effectively control the disease
Source-
- TamilNadu Agritech Portal
