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.
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.
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.