Question

Which of these infections are caused by viroid? A. Cauliflower mosaic B. Potato spindle mosaic C. Tobacco mosaic D. Tulip yellow mosaic

Answer 1

Hint: Viroid are small, circular RNA molecules with no protein coat. They generally infect some of the crop plants and the diseases caused by them are of economic importance.

Complete answer:
In 1961 T.O Diener discovered an infectious disease which is more tiny than viruses. It was found to be the free RNA and it lacks the protein coat which is found in the viruses. The RNA of the viroid is of molecular weight. Viroids are the smallest infectious pathogen known constituting nucleic acid but no protein coat. The mechanism of viroid replication uses RNA polymerase II, a host cell enzyme associated with the synthesis of messenger RNA from the DNA which instead catalyse the rolling circle synthesis of new RNA using viroid RNA as a template. Viroids cause the potato spindle Tuber disease which is susceptible to potato and tomato and no form of natural resistance can occur. In the potato the nutrient deficiency, spray damage, stunt growth, deformation of leaves and fruits and death of plants occurs. Hence the potato spindle tuber viroid is the first virus identified which causes this disease in potatoes and tomatoes.
Cauliflower mosaic contains circular double stranded DNA virus which is of the family Caulimoviridae. It infects vegetables like radish, cabbage and broccoli. The virus causes the discolouration of leaves and mottling. It is transmitted from plant to plant. Tobacco mosaic is the disease caused by tobacco mosaic virus mainly in tobacco and solanaceous plants. It was one of the first viruses discovered. The plants after getting infection start yellowing, curling in leaves and mottling. The seed coat is also infected by this virus.
Tulip yellow mosaic is the plant virus which leads to the breakage of colour in the tulip leaves. In lily the distorted leaves and flowers are seen due to this virus.

Hence, the correct answer is option (B).

Note: D.J Ivanowski discovered the virus. Virus contains nucleic acid as DNA and sometimes as RNA and a protein coat. They produce protein when they replicate. Most common disease caused by the virus is Tobacco mosaic virus in plants and AIDS in humans.