Question

Brown rust of wheat is caused by
A. Viruses
B. Bacteria
C. Fungi
D. Aphids

Answer 1

Wheat leaf rust or brown rust of wheat is a destructive disease that is most prevalent of all wheat rust diseases. It causes a serious threat to wheat in North America, South America, Mexico and India. The disease-causing pathogen is Puccinia triticina which belongs to the class Pucciniomycetes.

Complete answer: Fungal, bacterial, and viral infections are common destructive agents of economically important crops like wheat, barley, potato, rice, etc. Smuts and rusts are caused by fungal species and such diseases are commonly called mycosis of plants. Fungus species belonging to Basidiomycota and class Pucciniomycetes are most common parasitic species. These include the genus Puccinia. These are generally referred to as Puccinia rust fungus. The brown rust of the wheat is particularly caused by Puccinia triticina. It causes a destructive winter wheat infection that leads to $20$ loss in the yield. In India, it is a devastating seasonal disease. The infection cycle requires two hosts. The spores of the pathogenic fungus are called urediniospores. These spores start germinating when coming in contact with free moisture. The wind blows the spores and then spores are deposited over wheat leaf surfaces. The disease is characterized by the presence of small brown pustules on the leaf blades. These pustules are present in a randomly scattered distribution pattern. Disease onset is slow but it accelerates during temperatures above $15{}^\circ$C. The disease becomes serious when a complete overrun on the leaf surface is observed.
Hence, the right answer is option C.

Note: Triazole fungicides have been used to control the brown rust disease. The killing of the alternate host of P .triticina is usable in preventing the infection. Varietal resistant practices are fruitful in preventing devastating infections and destruction of wheat.