False smut / Lakshmi disease

Causal organism: Ustilaginoidea virens (Sexual stage: Villosiclava virens)

Symptoms:

• The fungus transforms individual ovaries/grains into greenish spore balls of velvety appearance.
• Few to several spikelets in a panicle are affected.

Pathogen:

• Sclerotia present in soil germinate and produce ascospores. They serve as primary source of inoculum.
• Chlamydospores are formed in the infected grains as spore balls which are spherical to elliptical, warty and olivaceous.
• Smut spores are air borne and responsible for secondary spread.

• Rainfall and cloudy weather during flowering and maturity, high soil nitrogen.

Management:

Preventive methods

• Grow moderately resistant varieties viz., CO 59.
• Use of disease-free seeds that are selected from healthy crop.
• Split application of nitrogen is recommended.
• Removal and proper disposal of infected plant debris.

Cultural methods:

• Among the cultural control, destruction of straw and stubble from infected plants is recommended to reduce the disease. .
• Early planted crop has less 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.

Chemical methods:

• Seed treatment with carbendazim 2.0g/kg of seeds.
• At booting and pre-flowering stages spray copper hydroxide 77 WP 800 gm or copper hydroxide 53.8% DF 600 ml or thifluzamide 15% + difenoconazole 20% SC 100 ml per acre.

Source of information:

• AICRIP rice, TNAU, Coimbatore, Rice diseases- online resource, IRRI, Phillippines.

Acknowledgements:

• IRRI, Phillippines