Black rust of wheat is caused by
A) Puccinia
B) Ustilago
C) Albugo
D) Phytophthora

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Hint: Black rust of wheat is a fungal disease. It affects wheat, barley, rye stems, leaves and grains. It causes great damage to the crops.

Complete Answer:
To solve this question, we must know about the disease and its pathogenic effect.
- Black rust is a fungal disease. It mostly infects the winter wheat.
- The infection can cause up to 20% yield loss. It causes small brown pustules on the leaf blades. If the plant gets severely affected, it develops patches. It spreads via airborne spores. - The wheat rust is majorly caused by the genus called Puccinia. Several species of this genus like tritici, rubigo-vera cause similar kinds of pathogenicity. Puccinia requires a moist climate to grow.
- The fungus can infect in less than three hours. More infection occurs with longer exposure to moisture. They grow best in a humid climate.
- The optimum temperature required for its growth is $15^\circ$ to $20^\circ$ C. Before sporulation, the wheat plant appears completely asymptomatic.

Thus the correct answer is (A) Puccinia causes Black rust in wheat.

Additional Information:
For controlling this disease, chemical like triazole fungicides can be used. But if the plant is severely affected, it is difficult to control. Nowadays farmers use a variety of wheat that is resistant to the disease.

Note: Wheat rust is a fungal disease which is caused by fungus called Puccinia. They cause dark patches in the leaves and stem. It can be controlled by the application of triazole fungicides.