Question

Which of the following is not a viral disease of plants?
A) Red rot of sugarcane
B) Tobacco mosaic disease
C) Leaf curl of tomato
D) Tristeza disease of citrus

Answer 1

Hint: It is widely known that animals get infected with a virus and develop diseases but very few know that plants also get infected with viruses and have diseases. Most of the plant viruses don't infect the animal cell. Same as animal viruses, plant viruses also don't have a mechanism to replicate without a host plant cell.

Complete answer:
Let's go through each option to find the correct answer.
The first option is the red rot of sugarcane. Red rot is a serious disease for sugarcane. This disease is caused by Red rot fungus (Colletotrichum falcatum Went). The symptoms of red rot disease include reddening of white patches of the stem, cavity inside the stem, mushy fungal growth, the leaves turn yellow and dry, etc.
Our second option is tobacco mosaic disease. Tobacco mosaic disease is caused by the tobacco mosaic virus which has single-stranded RNA as genetic material. This virus infects nine different families of plants. The symptoms of the infection in plants are discoloration of leaves, a mosaic pattern of light and dark color of green, etc.
The third option is the leaf curl of tomato which is caused by the Tomato yellow leaf curl virus. This virus has DNA as its genetic material.
The last option is Tristeza disease of citrus which is caused by the Tristeza citrus virus. The symptoms of this disease are highly variable and depend upon factors such as host, virulence, and environmental factors. Three major symptoms of CTV are pitting of stem, yellow seeds, and declined growth.

From the explanation, the correct answer is A which is red rot of sugarcane which is caused by fungus and not virus.

Note: Most of the plant viruses have RNA as their genetic material and few have DNA. Viruses that have RNA as their genetic material, infect plant cells, travel to the nucleus, and get converted into cDNA and get combined with the host's genome where they reproduce.