'Blast' is a serious fungal disease that commonly affects which crop?

Rice blast is one of the most destructive diseases of rice in the world. It is caused by the fungus Magnaporthe oryzae (also known as Pyricularia oryzae).

Symptoms of rice blast:

Leaf blast: spindle-shaped (diamond-shaped) spots on the leaves, with grey or whitish centres and brown or reddish borders. Severe infection can kill the leaves.

Node blast: the nodes of the stem turn black and break.

Neck blast (panicle blast): the base of the panicle (the neck) turns black and rots, so the panicle breaks or bears empty or partly filled grains. This form causes the greatest yield loss.

Conditions that favour blast:

• High humidity, long periods of leaf wetness (dew or rain), moderate temperatures (around 25 to 28 degrees Celsius) and cloudy weather.
• Excess nitrogen fertiliser increases susceptibility.
• Upland and rain-fed rice are often more affected.

How the disease spreads:

Fungal spores spread through air, water, infected seeds and crop residues.

Control measures:

• Growing resistant varieties.
• Treating seeds with fungicides before sowing.
• Balanced use of nitrogen fertiliser.
• Removing infected crop residues and weeds.
• Spraying fungicides such as tricyclazole when needed.

Other important diseases of rice:

• Bacterial leaf blight: caused by the bacterium Xanthomonas oryzae.
• Sheath blight: caused by the fungus Rhizoctonia solani.

Brown spot: caused by the fungus Bipolaris (Helminthosporium) oryzae. Brown spot was a major factor behind the Bengal Famine of 1943.

Tungro: a viral disease spread by leafhoppers.

False smut and khaira (a zinc deficiency disorder).

Diseases of other crops (for comparison):

• Wheat: rusts (black, brown and yellow), loose smut, karnal bunt.
• Cotton: wilt, root rot, leaf curl virus.
• Potato: late blight (the cause of the Irish Famine of the 1840s) and early blight.
• Mustard: white rust and Alternaria blight.
• Sugarcane: red rot.

Why not the other options?

• ✗Cotton is affected mainly by wilt, root rot and leaf curl virus.
• ✗Potato is affected mainly by early and late blight.
• ✗Mustard is affected mainly by white rust and Alternaria blight.