This set of Virology Multiple Choice Questions & Answers (MCQs) focuses on “Symptoms of Diseases Caused by Plant Viruses”.
1. Which of the following microorganisms causes oak-leaf pattern on leaves?
a) Bacteria
b) Fungi
c) Algae
d) Virus
View Answer
Explanation: The formation of oak-leaf pattern on leaves is an effect of infection by viruses. This symptom is commonly found in rose leaves caused by rose mosaic virus complex. The oak leaf pattern first appears on the older leaves of the plant and, as the disease progresses it spreads on the new leaves.
2. Which viruses do not show any symptoms after infecting the host?
a) Latent viruses
b) Infectious viruses
c) Waterborne viruses
d) Airborne viruses
View Answer
Explanation: Many viruses infect certain hosts without causing development of visible symptoms on them. These viruses are called latent viruses. The hosts of these viruses are called symptomless carriers. Wild plants are often infected with the latent viruses without any apparent disease symptoms. However, viruses that latently infect wild plants often cause disease symptoms in closely related crop plants leading to economic loss.
3. Which symptom of viral disease causes appearance of necrotic lesions on leaf?
a) Ring burn
b) Ring dot
c) Ring spot
d) Ring sphere
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Explanation: The appearance of dark area in plant tissues due to rapid cell death in that area upon infection is called necrotic lesion. Ring spots are characterized by the appearance of necrotic rings on the leaves and sometimes even on the fruits and stems. In many ring spot diseases, the symptoms tend to disappear later on but the virus remains inside the infected host.
4. Which of the following methods is used to detect virus-like infections in plants where no pathogens can be observed?
a) Indexing
b) Light microscopy
c) Microtomy
d) Anatomical study
View Answer
Explanation: In virus-like diseases of plants in which no pathogens can be observed identification of the pathogens, which are at presumed to be viruses, is made by indexing. Indexing involves inoculation by grafting of certain plant species or varieties called indicators. The indicators are sensitive to specific viruses and on inoculation with these viruses develop characteristic symptoms. Thus, development of the characteristic symptoms by an indicator identifies the virus with which the indicator was inoculated.
5. How can you perform PCR (Polymerase Chain Reaction) amplification of viral RNA of a plant with symptoms of viral infection?
a) By producing single-stranded RNA
b) By producing complementary DNA (cDNA)
c) By producing complementary RNA
d) By producing double-stranded RNA
View Answer
Explanation: The PCR technique allows unlimited amplification of selected specific DNA sequences for which suitable primers (short DNA sequences) are available. Reverse transcription of viral RNA into complementary DNA allows use of PCR amplification for virus RNA. After amplification of nucleic acid, the virus can be further detected by electrophoretic analysis of the PCR products.
6. Which of the following viruses causes formation of long, pointed, shoe-string like leaves in tomato?
a) Tomato mosaic virus
b) Tomato spotted wilt virus
c) Tomato rattle virus
d) Tomato dwarf virus
View Answer
Explanation: Tomato mosaic virus infects tomatoes and makes the leaflets long, pointed and sometimes shoe-string like. Infections of young plants reduce fruit set and may occasionally cause blemishes and internal browning on the fruits that are produced. Infected cells contain virus particles which can be seen easily with an electron microscope.
7. Which of the following viruses causes rhizomania disease of sugar beet?
a) Beet necrotic yellow vein virus
b) Beet curly top virus
c) Beet yellows virus
d) Beet western yellows virus
View Answer
Explanation: Beet necrotic yellow vein virus causes the rhizomania disease of sugar beets. The infected plants are generally stunted. This disease causes the root systems to decrease in size or excessive branching of the roots (rhizomania). It reduces the sugar content of the beets produced and yields are reduced drastically.
8. Which of the following crops is affected by Hordeiviruses?
a) Lettuce
b) Brinjal
c) Potato
d) Barley
View Answer
Explanation: The Hordeiviruses are named after barley (Hordeum) stripe mosaic virus. They primarily affect grain crops and wild grasses. Hordeivirus infections are relatively rare in nature but occurs wherever barley is grown. Infected plants show mosaics, chlorotic spots, yellow-brown stripes, and sometimes dwarfing and necrosis of plants.
9. Which of the following is a symptom of lettuce mosaic virus?
a) Crown gall formation
b) Canker formation
c) Mottling of the leaves
d) Small seed formation
View Answer
Explanation: Mottling of leaves is a characteristic symptom of lettuce mosaic virus. In the advance stages of infection, this virus causes distortion and necrosis of the leaf margins. Finally, stunted plants are produced and proper lettuce heads are not formed leading to economic losses. Crop plants like pea and flowering plants like sweet pea, marigold and zinnia are also infected by the lettuce mosaic virus.
10. Viroid can infect both plants and animals.
a) True
b) False
View Answer
Explanation: Infectious particle that lacks a protein coat and exists as free naked RNA is called viroid. Viroid can infect plant cells and cause diseases. No viroid infection has been reported in humans or animals. Viroid infection in plants results in distortion of fruit, necrosis of leaf and stem and dwarfing of the plant. These symptoms are very similar to virus infection and is difficult to differentiate.
11. Which of the following is a symptom of Tobravirus infection?
a) Chlorosis of leaf
b) Cytoplasmic inclusion
c) Stem rot
d) Leaf rot
View Answer
Explanation: Tobravirus causes the formation of cytoplasmic inclusions inside the infected cells. The cytoplasmic inclusions of Tobraviruses can be identified by their perpendicular arrangement outside the mitochondria. In tobacco plants, crumpled leaves and formation of necrotic lesions on stems and leaf veins are also symptoms of Tobravirus infection.
12. Which of the following is a symptom of Bean common mosaic virus?
a) Necrotic lesion
b) Malformation of pods
c) Root rot
d) Stem elongation
View Answer
Explanation: Malformation of pods is one of the most common symptoms of Bean common mosaic virus. Plants infected with the virus also show mottling, yellowing, and malformation of leaves. Infected plants are stunted and bunchy, seeds may be aborted, smaller, or malformed, and yields may be reduced by up to 80 to 100%, depending on the plant stage of growth at the time of infection.
13. Which of the following is a symptom of Plum pox virus?
a) Stunted growth
b) Branching of root
c) Pox symptoms on infected fruits
d) Pox symptoms on leaves
View Answer
Explanation: Plum fruits of plants infected with Plum pox virus develop severe pox symptoms which include dark-colored rings or patches on the skin, brown or reddish discoloration in the flesh, and brown spots on the stones. The infected fruits fall down before maturation. Other symptoms of this virus are severe mottling, diffuse or bright rings, or vein yellowing and elongated line patterns on infected leaves.
14. Which of the following viruses causes lichen-like lesions on infected fruits?
a) Papaya ring spot
b) Tobacco mosaic virus
c) Tobacco rattle virus
d) Lettuce mosaic virus
View Answer
Explanation: Fruits produced after papaya ring spot virus infection exhibit lichen-like lesions. Fruits of the infected plants are usually small, show ring spots, uneven bumps and have an unpleasant taste. Trees infected at a very young age remain stunted and never produce any fruit. Symptoms on leaf include intense yellow mosaic pattern and small shoestring-like new leaves.
15. Virus particles of Potexviruses are visible under light microscope.
a) True
b) False
View Answer
Explanation: Potexviruses produce large numbers of virus particles in the cytoplasm of infected cells. The virus particles form large aggregates visible even under the light microscope. Potexviruses infect potato and orchids causing significant losses. The plants infected by potexviruses are shorter in size and produce less fruits.
Sanfoundry Global Education & Learning Series – Virology.
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